1587884932985_final book 26-04-20

Coal as Fossils –

Coal, one of the most important primary fossil fuels, a solid carbon-rich
material that is usually brown or black and most often occurs in stratified
sedimentary deposits.
But fossil fuels come with a cost. Coal smoke is linked with everything from asthma
and birth defects to cancer and premature death.

Conversion -

In general, coal can be considered a hydrogen-deficient hydrocarbon with a
hydrogen-to-carbon ratio near 0.8, as compared with a liquid hydrocarbons ratio near 2
(for propane, ethane, butane, and other forms of natural gas) and a gaseous hydrocarbons
ratio near 4 (for gasoline). For this reason, any process used to convert coal to alternative
fuels must add hydrogen (either directly or in the form of water).

World Distribution of Coal -

Coal is a widespread resource of energy and chemicals. Although terrestrial plants
necessary for the development of coal did not become abundant until Carboniferous time
(358.9 million to 298.9 million years ago), large sedimentary basins containing rocks of
Carboniferous age and younger are known on virtually every continent, including Antarctica
(not shown on the map).

6.8.1 Properties Of Coal -

Density –

Coal density ranges from approximately 1.1 to about 1.5 megagrams per cubic metre, or
grams per cubic centimetre Coal is slightly denser than water and significantly less dense
than most rock and mineral matter.

Porosity-

Most of the effective surface area of a coal—about 200 square metres per gram—is not on
the outer surface of a piece of coal but is located inside the coal in its pores. The presence
of pore space is important in the production of coke, gasification, liquefaction, and the
generation of high-surface-area carbon for purifying water and gases.

Reflectivity-

Reflectivity is measured by shining a beam of monochromatic light (with a wavelength of
546 nanometres) on a polished surface of the vitrinite macerals in a coal sample and
measuring the percentage of the light reflected with a photometer. Vitrinite is used
because its reflectivity changes gradually with increasing rank.

Other properties-

Hardness and grindability determine the kinds of equipment used for mining, crushing,
and grinding coals in addition to the amount of power consumed in their operation. Ash-
fusion temperature influences furnace design and operating conditions.

The ash that is a by-product of
coal is used as fillers for things
such as tennis rackets, golf balls
and linoleum.

6.8.2 Types of Coal:

As geological processes apply pressure to dead biotic material over time, under suitable
conditions, its metamorphic grade or rank increases successively into:

• Peat, a precursor of coal
• Lignite, or brown coal, the lowest rank of coal, most harmful to health,[21] used almost

exclusively as fuel for electric power generation
o Jet, a compact form of lignite, sometimes polished; used as an ornamental stone

since the Upper Palaeolithic
• Sub-bituminous coal, whose properties range between those of lignite and those of

bituminous coal, is used primarily as fuel for steam-electric power generation.
• Bituminous coal, a dense sedimentary rock, usually black, but sometimes dark brown,

often with well-defined bands of bright and dull material. It is used primarily as fuel in
steam-electric power generation and to make coke.
• Anthracite, the highest rank of coal is a harder, glossy black coal used primarily for
residential and commercial space heating.
• Graphite is difficult to ignite and not commonly used as fuel; it is most used in pencils, or
powdered for lubrication.
We will mainly discuss four types of coal –

(1) Peat –

Peat forms when plant material does not fully decay in acidic and anaerobic conditions. It is
composed mainly of wetland vegetation: principally bog plants including mosses, sedges,
and shrubs. As it accumulates, the peat holds water. This slowly creates wetter conditions
that allow the area of wetland to expand. Peatland features can include ponds, ridges,
and raised bogs. The characteristics of some bog plants actively promote bog formation. For
example, Sphagnum mosses actively secrete tannins, which preserve organic material.

Sphagnum also have special water retaining cells, known as Hyaline cells, which can release
water ensuring the bog land remains constantly wet which helps promote peat production.

Characteristics and uses -

Under pressure, water is forced out of peat, which is soft and easily compressed, and once
dry can be used as fuel. In many countries, including Ireland and Scotland, peat has
traditionally been used for cooking and domestic heating, and peat is stacked to dry in rural
areas. It remains harvested on an industrial scale for this purpose in countries such as
Ireland and Finland. Its insulating properties make it useful in industry.

Although humans have many uses for peat, it presents severe problems at times. Wet or
dry, it can be a major fire hazard. Peat fires may burn for great lengths of time, or smoulder
underground and reignite after winter if an oxygen source is present. Because they are
easily compressed under minimal weight, peat deposits pose major difficulties to builders of
structures, roads, and railways. When the West Highland railway line was built
across Rannoch Moor in western Scotland, its builders had to float the tracks on a multi-
thousand-ton mattress of tree roots, brushwood, earth and ash.

Peatland can also be an important source of drinking water providing nearly 4% of all
potable water stored in reservoirs. In the UK, more than 28 million people use drinking
water from water sources which rely on peatlands.

(2) Lignite – Tinnunculite is a naturally

occurring material that only
forms when falcon’s poop

directly into burning coal

mines as they fly

Sometimes called “brown coal,” lignite is the lowest quality and most crumbly coal. This
softer and geologically “younger” coal sits relatively close to the earth’s surface.
Lignite can be broken down chemically through coal gasification, the process of producing
syngas from coal along with water, air and/or oxygen. This creates synthetic natural gas that
delivers more power and is easier to operate in commercial-scale electric generations.

Characteristics of Lignite Coal -

Of all coal types, lignite contains the lowest level of fixed carbon (25-35%) and the highest
level of moisture (typically 20-40% by weight, but can go as high as 60-70%). Ash varies by
up to 50% by weight. Lignite has low levels of sulfur (less than 1%) and ash (approximately
4%), but it has high levels of volatile matter (32% and higher by weight) and produces high

levels of air pollution emissions. Lignite has a heating value of approximately 4,000 to 8,300
Btu per pound.

(3) Bituminous

Bituminous coal, also called soft coal, the most abundant form of coal, intermediate in rank
between subbituminous coal and anthracite according to the coal classification used in the
United States and Canada. In Britain bituminous coal is commonly called “steam coal,” and
in Germany the term Steinkohle (“rock coal”) is used. In the United States and Canada
bituminous coal is divided into high-volatile, medium-volatile, and low-volatile bituminous
groups. High-volatile bituminous coal is classified on the basis of its calorific value on a
moist, ash-free basis (ranging from 24 to 33 megajoules per kilogram; 10,500 to 14,000
British thermal units per pound), while medium-volatile and low-volatile bituminous coals
are classified on the basis of the percentage of fixed carbon present on a dry, ash-free basis
(ranging from 69 to 78 percent for medium-volatile and from 78 to 86 percent for low-
volatile bituminous coal). Medium-volatile and low-volatile bituminous coals typically have
calorific values near 35 megajoules per kilogram (15,000 British thermal units per pound) on
a dry, ash-free basis
Characteristics of bituminous coal -

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(4) Anthracite -

Anthracite coal, mined from the planet's oldest geological formations, has spent the longest
time underground. The coal has been subjected to the most pressure and heat, making it
the most compressed and hardest coal available. Hard coal contains greater potential to
produce heat energy than softer, geologically "newer" coal.

Characteristics of Anthracite -
Anthracite contains a high amount of fixed carbon—80 to 95 percent—and very low sulfur
and nitrogen—less than 1 percent each. Volatile matter is low at approximately 5 percent,
with 10 to 20 percent ash possible. Moisture content is roughly 5 to 15 percent. The coal is
slow-burning and difficult to ignite because of its high density, so few pulverized, coal-fired
plants burn it.

6.8.3 Analysis of Coal –

Coal Analysis techniques are specific analytical methods designed to measure the particular
physical and chemical properties of coals. There are two methods to analyse coal which are
called proximate analysis and ultimate analysis.
The proximate analysis determines only the fixed carbon, volatile matter, moisture and ash
percentages and it can be determined with a simple apparatus.
The ultimate analysis determines all coal component elements, solid or gaseous and it
needs properly equipped laboratory with skilled chemists.

(1) Proximate analysis:-

The proximate analysis of coal separates the products into four groups:
(1) moisture, (2) volatile matter, consisting of gases and vapors driven off during pyrolysis,
(3) fixed carbon, the non-volatile fraction of coal, and (4) ash, the inorganic residue
remaining after combustion. The proximate analysis of coal is presented as a group of test

methods that has been used widely as the basis for coal characterization in connection with
coal.

Proximate analysis gives the gross composition of the biomass and hence it is relatively
easy to measure. One can do this without any elaborate set up or expensive analytical
equipment. For wood fuels, we can use standard E-870-06. Separate ASTM standards are
applicable for determination of the individual components of biomass as listed.

Moisture:

Moisture increases in transport costs and reduces the efficiency of fuel.
For equilibrium moisture in coal one could use D-1412-07. In these protocols, a weighed
sample of the fuel is heated in an air oven at 103°C and weighed after cooling. To ensure
complete drying of the sample, the process is repeated until its weight remains unchanged.
The difference in weight between a dry and a fresh sample gives the moisture content in the
fuel.
Standard E-871-82, for example, specifies that a 50 g wood sample be dried at 103°C for 30
min. It is left in the oven at that temperature for 16 h before it is removed and weighed. The
weight loss gives the moisture (M) of the proximate analysis.
FORMULA-
%of moisture = (loss in weight)/ (weight of coal) *100

The amount of energy produced by the sun
in a two-week period equals the combined
stored energy of all the coal, iron, and
natural gas reserves known to man.

Volatile Matter:

Bituminous coal contains more volatile matter than anthracite coal. Lesser the content of
volatile matter ,better is the quality of coal. This sample is ground to less than 1 mm in size
through cutting or shearing, and 1 g is taken from it. The sample is put in a covered crucible,
so as to avoid contact with air, during devolatilization. The covered crucible is placed in a
furnace maintained at 950 ± 20°C. The volatiles released are detected by luminous flame
observed from the outside. The crucible is heated for 7 min. After 7 min, the crucible is
taken out, cooled in a desiccator, and weighed as soon as possible to determine the weight
loss due to devolatilization.
FORMULA -
% of volatile matter = (loss in weight)/ (weight of moisture free coal) * 100

Ash:

Ash content reduces the calorific value of the fuel. It creates cleaning and disposals
problems,also hindrance in the flow of heat. For coal or coke, standard D-3174-04 may be
used. Here a 1.0 g sample (pulverized below 250 μm) is dried under standard conditions
and heated to 450–500°C for the first 1 h and then to 700–750°C (950°C for coke) for the
second 1 h. The sample is heated for 2 h or longer at that temperature to ensure that the
carbon is completely burnt. It is then removed from the furnace, cooled, and weighed.
FORMULA-
% of ash = (weight of residue)/ (weight of dried coal) * 100

Fixed carbon by difference:

The moisture and ash determined in proximate analysis refer to the same moisture and ash
determined in ultimate analysis. However, the fixed carbon in proximate analysis is different
from the carbon in ultimate analysis. In proximate analysis, it does not include the carbon in
the volatile matter and is often referred to as the char yield after devolatilization
FORMULA -
% Fixed C = 100 - (% of moisture + %V matter + % Ash)

+

(2) Ultimate analysis -

Ultimate analysis provides a convenient method for reporting the major organic
elemental composition of coal. For this analysis, a coal sample is combusted in an ultimate
analyzer, which measures the weight percent of carbon, hydrogen, nitrogen, sulphur, and
ash from a coal sample. The total carbon, hydrogen, and nitrogen are determined at the
same time from the same sample in the analyzer. Total oxygen is calculated from the other
values.

Total carbon:

Total carbon can be measured in an ultimate analyser as part of the ultimate analysis, or in a
carbon-sulfur analyzer. Both machines are calibrated using standard reference samples of
known carbon, hydrogen, nitrogen, sulfur and ash values. In the carbon-sulfur analyzer, 0.25
grams of sample are placed in a specialized sample vial made from refractory-grade clay.
The vial is then combusted at a temperature of 1350 °C.

When coal is combusted, the carbon is liberated as carbon dioxide (CO2) and as
hydrocarbons (CH4). CO2 comes from the organic compounds in coal, but can also be
liberated from carbonate (e.g., calcite–CaCO3) minerals in the inorganic fraction of a coal,
if they are present. This means that the total carbon measurement may include carbon
from the mineral fraction as well as the organic fraction of the coal.

To determine the inorganic (mineral) carbon and organic carbon components of a total
carbon sample, a split of the sample should be analyzed in a coulometer. The carbon
measured in a coulometer is total organic carbon, sometimes denoted as TOC. With a
coulometer measure of total organic carbon and ultimate analysis or carbon-sulfur
analysis measurement of total carbon, the various components of carbon can be
calculated:

Total carbon (from ultimate or c-s analyzer) = Total inorganic carbon + total organic
carbon (from coulometer)
Total organic carbon (from coulometer) = Total carbon (from ultimate or c-s analyzer) –
total inorganic carbon (from coulometer)
Total inorganic carbon = Total carbon (from ultimate or c-s analyzer) – total inorganic carbon
(from coulometer)

FORMULA -
% of C = (increase in weight of KOH tube *12 *100)/ (weight of coal sample
) *44

Total hydrogen:

Total hydrogen in the ultimate analysis is the measured weight percent of
hydrogen in the coal. Hydrogen is liberated from coal during combustion as water vapor
(H2O), which can come from the organic compounds in coal, inherent moisture in coal, and
the breakdown of clay minerals in the inorganic fraction of the coal (Thomas,
1992). Hydrogen values from an ultimate analyzer then need to be corrected to factor
out hydrogen derived from moisture. This is especially important in low rank coals which

have higher moisture contents. To correct the measured (as determined) hydrogen from
the analyzer to fuel-based hydrogen (as received) value:

Hydrogen (fuel-based) = Hydrogen (as received, analyzer measurement) – ((0.1119 *
moisture (as determined, measured from the ultimate analyzer)

FORMULA -
% of H = (increase in weight of CaCl2 tube *2*100)/ (weight of coal sample taken)
*18

Total oxygen:

Essentially, total oxygen content is the remaining major element of the five major
elements in coal–carbon, hydrogen, oxygen, nitrogen, sulfur–in addition to the non-
combustible ash in coal. The total oxygen content is calculated from the measured (as-
determined) values for the major elements and ash:

Total oxygen weight % = 100 – (total carbon weight % + total hydrogen weight % +
total nitrogen weight % + total sulfur weight % + total ash weight%)
Similar to hydrogen, the measured oxygen (as determined) value from the ultimate
analyzer may also contain oxygen derived from moisture in the sample. To correct for a
fuel-based oxygen (as received) value:

Total oxygen (fuel-based, weight %) = Total oxygen (analyzer measured, weight %)
– ((0.8881 * moisture (analyzer measured, as determined, weight %)

Total nitrogen:

Total nitrogen in the ultimate analysis is expressed as the measured weight percent of
nitrogen in the coal. It is determined by ASTM method D5373-08 (American Society for
Testing and Materials, 2013, p. 628–636).

Nitrogen is mostly found in the organic fraction of coal. Upon combustion, it is liberated as
nitrogen oxides in the flue gas (emissions). NOX emissions from coal combustion are
regulated in the United States. They are an environmental concern because they combine
with water vapor to produce nitric acid (HNO3), which contributes to acid rain (Energy
Information Administration, 2001).
FORMULA -
% of N = (volume of acid *Normality *1.4)/(weight of coal taken)

Total sulphur:

Total sulphur in the ultimate analysis is the measured weight percent of sulphur in
the coal. It is determined by ASTM methods D5373-08, or D4239-02 (American Society for
Testing and Materials, 2013, p. 628–636, 556–561, respectively). In the test, a coal sample is
ground to a set size and weighed, then placed in a suphur analyzer. In the analyzer, the
sample is combusted at a temperature of 1,370°C in an oxygen atmosphere. The oxygen
reacts with sulphur to form sulphur dioxide gas. The gas passes through an infrared
absorption detector in the analyzer, which measures the concentration of sulphur.

Sulphur in coal occurs in three forms: (1) organic, (2) inorganic, and (3) elemental.
Inorganic sulphur occurs mostly in minerals such as pyrite (FeS2). An additional test of
sulphur forms can be run to determine the relative amount of the three forms of sulphur
in a coal that contribute to the total sulphur value determined by ultimate analysis.
FORMULA -
% of S = (weight of BaSO4 obtained *32*100)/233*(weight of coal sample taken in the
bomb)

Here is a small quiz:

1. Washing of coal decreases its-

a) Caking index

b) Mineral matter content

c) Ash content

d) Both (b) and (c) (Ans. b)

2. The optimum percentage of excess air for combustion

depends upon the __________ of the fuel.

a) Type (solid, liquid or gaseous)

b) Calorific value

c) Sulphur content

d) Ignition temperature (Ans. a)

3. _________ of the coal is the basis for seylor’s coal

classification.

a) Proximate Analysis

b) Ultimate Analysis

c) Caking index

d) Calorific value (Ans. b)

4. Spontaneous combustion of coal on storage results due to

a) Inadequate ventilation

b) Low temperature oxidation

c) Storage in large heaps with small surface to volume

ratio

d) All (a), (b) and (c) (Ans. d)

5. To avoid fire by spontaneous combustion of coal due to its

Low temperature oxidation, it should be stored in

a) Shallow and small piles

b) Fine sizes without the presence of any lumps

c) Closed space without any ventilation facility

d) Large heaps with small surface to volume ratio (Ans.a)

6.9 Liquid fuel:

Liquid fuels are combustible or energy-generating molecules that can be harnessed
to create mechanical energy, usually producing kinetic energy; they also must take the
shape of their container. It is the fumes of liquid fuels that are flammable instead of the
fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are
several types, such as hydrogen fuel (for automotive uses), ethanol, and biodiesel, which
are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation
and the economy.

Liquid fuels are contrasted with solid fuels and gaseous fuels.

General properties -

Some common properties of liquid fuels are that they are easy to transport, and can be
handled with relative ease. Physical properties of liquid fuels vary by temperature, though
not as greatly as for gaseous fuels. Some of these properties are: flash point, the lowest
temperature at which a flammable concentration of vapor is produced; fire point, the

temperature at which sustained burning of vapor will occur; cloud point for diesel fuels, the
temperature at which dissolved waxy compounds begin to coalesce, and pour point, the
temperature below which the fuel is too thick to pour freely. These properties affect the
safety and handling of the fuel.

6.9.1 Types of liquid fuel -
Petroleum:

Most liquid fuels used currently are produced from petroleum. The most notable of these is
gasoline. Scientists generally accept that petroleum formed from the fossilized remains of
dead plants and animals by exposure to heat and pressure in the Earth's crust.

Gasoline:

-

Gasoline is the most widely used liquid fuel. Gasoline, as it is known in United States and
Canada, or petrol virtually everywhere else, is made of hydrocarbon molecules (compounds
that contain hydrogen and carbon only) forming aliphatic compounds, or chains of carbons
with hydrogen atoms attached. However, many aromatic compounds (carbon chains
forming rings) such as benzene are found naturally in gasoline and cause the health risks
associated with prolonged exposure to the fuel.
Production of gasoline is achieved by distillation of crude oil. The desirable liquid is
separated from the crude oil in refineries. Crude oil is extracted from the ground in several

processes, the most commonly seen may be beam pumps. To create gasoline, petroleum
must first be removed from crude oil.

Diesel:

Conventional diesel is similar to gasoline in that it is a mixture of aliphatic hydrocarbons
extracted from petroleum. Diesel may cost more or less than gasoline, but generally costs
less to produce because the extraction processes used are simpler. Some countries
(particularly Canada, India and Italy) also have lower tax rates on diesel fuels.
After distillation, the diesel fraction is normally processed to reduce the amount of
sulfur in the fuel. Sulphur causes corrosion in vehicles, acid rain and higher emissions of
soot from the tail pipe (exhaust pipe). Historically, in Europe lower sulfur levels than in
the United States were legally required.
A diesel engine is a type of internal combustion engine which ignites fuel by injecting it into a
combustion chamber previously compressed with air (which in turn raises the temperature)
as opposed to using an outside ignition source, such as a spark plug.

Kerosene:

Kerosene is used in kerosene lamps and as a fuel for cooking, heating, and small
engines. It displaced whale oil for lighting use. Jet fuel for jet engines is made in several
grades (Avtur, Jet A, Jet A-1, Jet B, JP-4, JP-5, JP-7 or JP-8) that are kerosene-type
mixtures. One form of the fuel known as RP-1 is burned with liquid oxygen as rocket
fuel. These fuel grade kerosenes meet specifications for smoke points and freeze
points.

The engine would start on gasoline, then switch over to kerosene once the engine warmed
up. A "heat valve" on the manifold would route the exhaust gases around the intake pipe,
heating the kerosene to the point where it can be ignited by an electric spark.

Liquefied petroleum gas (LPG):

LP gas is a mixture of propane and butane, both of which are easily compressible gases
under standard atmospheric conditions. It offers many of the advantages of compressed
natural gas (CNG), but does not burn as cleanly, is denser than air and is much more easily
compressed. Commonly used for cooking and space heating, LP gas and compressed
propane are seeing increased use in motorized vehicles; propane is the third most
commonly used motor fuel globally.

Non-petroleum fossil fuels -

Synthetic fuel:

-

When petroleum is not easily available, chemical processes such as the Fischer-Tropsch
process can be used to produce liquid fuels from coal or natural gas. Synthetic fuels from
coal were strategically important during World War II for the German military. Today
synthetic fuels produced from natural gas are manufactured, to take advantage of the
higher value of liquid fuels in transportation.

Natural gas:

Natural gas, composed chiefly of methane, can be compressed to a liquid and used as a
substitute for other traditional liquid fuels. Its combustion is very clean compared to
other hydrocarbon fuels, but the fuel's low boiling point requires the fuel to be kept at
high pressures to keep it in the liquid state. Though it has a much lower flash point than
fuels such as gasoline, it is in many ways safer due to its higher autoignition temperature
and its low density, which causes it to dissipate when released in air.

Biodiesel:

Biodiesel is similar to diesel but has differences akin to those between petrol and ethanol.
For instance, biodiesel has a higher cetane rating (45-60 compared to 45-50 for crude-oil-
derived diesel) and it acts as a cleaning agent to get rid of dirt and deposits.
/

Alcohols:

Generally, the term alcohol refers to ethanol, the first organic chemical produced by
humans, but any alcohol can be burned as a fuel. Ethanol and methanol are the most
common, being sufficiently inexpensive to be useful.

Methanol:

Methanol is the lightest and simplest alcohol, produced from the natural gas component
methane. Its application is limited primarily due to its toxicity (similar to gasoline), but
also due to its high corrosivity and miscibility with water. Small amounts are used in
some types of gasoline to increase the octane rating. Methanol-based fuels are used in
some race cars and model aeroplanes.

Hydrogen:

Liquefied hydrogen is the liquid state of the element hydrogen. It is a common liquid rocket
fuel for rocket applications and can be used as a fuel in an internal combustion engine or
fuel cell. Various concept hydrogen vehicles have been lower volumetric energy, the
hydrogen volumes needed for combustion are large. Hydrogen was liquefied for the first
time by James Dewar in 1898.

6.9.2 Refining of crude oil-

The primary uses of crude oil to this point have been in the production of fuel. A single
barrel of crude oil can produce the following components, which are listed by percent of the
barrel they constitute.

• 42% Gasoline
• 22% Diesel
• 9% Jet Fuel
• 5% Fuel Oil
• 4% Liquefied Petroleum Gases
• 18% Other products

Refining:

Petroleum refining refers to the process of converting crude oil into useful products. Crude
oil is composed of hundreds of different hydrocarbon molecules, which are separated
through the process of refining. The process is divided into three basic steps: separation,
conversion, and treatment.

Separation:

Separation refers to the process of distillation. Crude oil is heated in a furnace so that
hydrocarbons can be separated via their boiling point. Inside large towers, heated
petroleum vapors are separated into fractions according to weight and boiling point. The
lightest fractions, which include gasoline, rise to the top of the tower before they condense

back to liquids. The heaviest fractions will settle at the bottom because they condense
early.

Conversion:

Conversion is simply the process of changing on kind of hydrocarbon into another. Of the,
the desired product is gasoline. Cracking is the process of taking heavier, less valuable
fractions of crude and converting them into lighter products. Cracking uses heat and
pressure to break heavier elements into lighter ones. Alkylation is another common
process, which is basically the opposite of cracking. In alkylation, small gaseous byproducts
are combined to form larger hydrocarbons.

Treatment:

Treatment is the final process of refining, and includes combining processed products to
create various octane levels, vapor pressure properties, and special properties for products
used in extreme environments. One common example of treatment is the removal of sulfur
from diesel fuel, which is necessary for it to meet clean air guidelines. Treatment is highly
technical and is the most time-consuming step of refining.

6.10 Knocking -

Knocking (also knock, detonation, spark knock, pinging or pinking) in spark ignition
internal combustion engines occurs when combustion of some of the air/fuel mixture in
the cylinder does not result from propagation of the flame front ignited by the spark plug,
but one or more pockets of air/fuel mixture explode outside the envelope of the normal
combustion front. The fuel-air charge is meant to be ignited by the spark plug only, and at a
precise point in the piston's stroke. Knock occurs when the peak of the combustion process
no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates
the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically.
Effects of engine knocking range from inconsequential to completely destructive.

Knocking should not be confused with pre-ignition—they are two separate events.
However, pre-ignition can be followed by knocking.

The phenomenon of detonation was first observed and described by Harry Ricardo
during experiments carried out between 1916 and 1919 to discover the reason for
failures in aircraft engines.

Knock detection:

Due to the large variation in fuel quality, a large number of engines now contain
mechanisms to detect knocking and adjust timing or boost pressure accordingly in order
to offer improved performance on high octane fuels while reducing the risk of engine
damage caused by knock while running on low octane fuels.

An early example of this is in turbo charged Saab H engines, where a system called
Automatic Performance Control was used to reduce boost pressure if it caused the engine
to knock.

Various monitoring devices are commonly utilized by tuners as a method of seeing and
listening to the engine in order to ascertain if a tuned vehicle is safe under load or used to
re-tune a vehicle safely. A commonly used type of knock sensor consists of a Piezoelectric
sensor attached to the engine block, tuned to detect the sound of knocking.

Knock prediction:

Since the avoidance of knocking combustion is so important to development engineers, a
variety of simulation technologies have been developed which can identify engine design
or operating conditions in which knock might be expected to occur. This then enables
engineers to design ways to mitigate knocking combustion whilst maintaining a high
thermal efficiency.

Since the onset of knock is sensitive to the in-cylinder pressure, temperature and
autoignition chemistry associated with the local mixture compositions within the
combustion chamber, simulations which account for all of these aspects [5] have thus
proven most effective in determining knock operating limits and enabling engineers to

determine the most appropriate operating strategy.

Knock control:

The objective of knock control strategies is to attempt to optimize the trade-off between
protecting the engine from damaging knock events and maximizing the engine’s output
torque. Knock events are an independent random process. It is impossible to design knock
controllers in a deterministic platform. A single time history simulation or experiment of
knock control methods are not able to provide a repeatable measurement of controller’s
performance because of the random nature of arriving knock events. Therefore, the desired
trade-off must be done in a stochastic framework which could provide a suitable
environment for designing and evaluating different knock control strategies performances
with rigorous statistical properties.

6.10.1 Petrol Engine –

Petrol engines harness the energy created by petrol in the core of a car engine to propel the
vehicle. Petrol is a high-energy fuel that releases large amounts of energy when ignited in an
internal combustion engine.
Cars use a four-stroke combustion cycle, or Otto cycle, to convert gasoline into kinetic
energy. The four strokes include the intake stroke, compression stroke, combustion stroke
and exhaust stroke. The intake stroke starts the combustion process by allowing the engine
to take in a cylinder-full of air and gasoline. After this process, air is compressed through the
movement of the pistons in the engine. Upon compression, a spark plug emits a spark to
ignite the gasoline and causes a controlled explosion in the cylinder. The resulting explosion
causes the piston to move downward, which causes the exhaust valve to open and release
exhaust out the tailpipe.
Petrol, also known as "crude oil," consists of carbon and hydrogen atoms that split apart
when burned. The combustion process in a petrol engine occurs when the carbon and
hydrogen combine with oxygen from the air to make carbon dioxide gas and water.
Although the petrol engine revolutionized vehicular transport, experts claim it is the cause
of pollution and global
warming. As a result, hybrid cars that use a combination of electricity and gasoline power
are becoming increasingly popular among environmentally-conscious drivers.

6.10.2 Diesel engines -

Basically, there are two types of diesel engine types - the Four Stroke and Two Stroke. The
'Diesel Cycle' uses higher Compression-Ratio. It was named after German engineer Rudolph
Diesel, who invented and developed first Four-Stroke diesel engine. The four strokes of the

diesel cycle are similar to that of a petrol engine. However, the 'Diesel Cycle' considerably
defers by the way the fuel system supplies the diesel the engine and ignites it.
A conventional internal combustion diesel engine works on 'Diesel Cycle'. In the simple diesel
engines, an injector injects diesel into the combustion chamber above the piston directly. The
'Compression-Ignition engine' is also another name for the Diesel engine. This is mainly
because it burns the diesel with hot and compressed air. The temperature of the air inside
the combustion chamber rises to above 400°c to 800°c. This, in turn, ignites the diesel injected
into the combustion chamber. Thus, the 'Diesel Cycle' does not use an external mechanism

such as a spark-plug to ignite the air-fuel mixture.
The Four-Stroke diesel engine works on the following cycle:

1. Suction Stroke – With pistons moving downwards and the opening of the inlet valve
creates the suction of clean air into the cylinders.

2. Compression – With the closing of Inlet valve the area above the piston gets closed. The
piston moves up resulting in compression of the air in a confined space under higher
compression-ratio.

Combustion Process - At this stage, the injector sprays the diesel into the combustion
chamber. The rise in temperature of the air caused by its compression; results in
instantaneous burning of diesel with an explosion. This causes heat to release which
generates expanding forces known as power.

3. Power Stroke – Furthermore, these forces again push the pistons downwards resulting in
their reciprocating motion.

Diesel Power Stroke

4. Exhaust Stroke – On their way up, the pistons push the exhaust gases above them thru’ the
exhaust valve which opens during the exhaust stroke.

Diesel Exhaust Stroke
This cycle repeats itself until the engine turns off, resulting in the continuance of engine’s
running.

4 Stroke Diesel Engine Animation
A diesel engine is mainly classified into two types - Indirect-Injection (IDI) & Direct-injection
(DI). The Direct-Injection diesel cycle was an earlier generation technology. It later evolved
into its successor & more advanced CRDi. Earlier generation utility vehicles, trucks, buses &
generators still widely use the simple DI engines. Furthermore, sophisticated & refined CRDi
engines became very popular in the Sedans, MPVs, SUVs and Luxury cars in the recent past.

6.10.3 Octane Number:-

An octane rating, or octane number, is a standard measure of the performance of an
engine or aviation fuel. The higher the octane number, the more compression the fuel can
withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are
used in high-performance gasoline engines that require higher compression ratios. In
contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel
engines, because diesel engines (also referred to as compression-ignition engines) do not
compress the fuel, but rather compress only air and then inject fuel into the air which was

heated by compression. Gasoline engines rely on ignition of air and fuel compressed
together as a mixture, which is ignited at the end of the compression stroke using spark
plugs. Therefore, high compressibility of the fuel matters mainly for gasoline engines. Use of
gasoline with lower octane numbers may lead to the problem of engine knocking.

Definition:

The percentage by volume of iso-octane in a mixture of iso-octane and n-heptane which
just matches the knocking characteristics of a fuel undertest (n-heptane knocks very badly
and has poor resistant to knocking, has zero octane value. Iso-octane has good resistant to
knocking and has octane value 100).
The octane rating of gasoline is measured in a test engine and is defined by
comparison with the mixture of 2,2,4-trimethylpentane (iso-octane) and heptane that
would have the same anti-knocking capacity as the fuel under test: the percentage, by
volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel. For
example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane
and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the
gasoline contains just iso-octane and heptane in these proportions, but that it has the
same detonation resistance properties (generally, gasoline sold common use never
consists solely of iso-octane and heptane; it is a mixture of many hydrocarbons and often
other additives).

Measurement methods:

A US gas station pump offering five different (R+M)/2 octane ratings
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON).
RON is determined by running the fuel in a test engine with a variable compression ratio
under controlled conditions, and comparing the results with those for mixtures of iso-
octane and n-heptane. The Compression ratio is varied during the test in order to
challenge the fuel's antiknocking tendency as an increase in the compression ratio will
increase the chances of knocking.

Motor Octane Number (MON):

Another type of octane rating, called Motor Octane Number (MON), is determined at 900
rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine
to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and
variable ignition timing to further stress the fuel's knock resistance. Depending on the

composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane
lower than the RON, but there is no direct link between RON and MON.

Observed Road Octane Number (RdON):

Another type of octane rating, called Observed Road Octane Number (RdON), is derived
from testing gasolines in real world multi-cylinder engines, normally at wide open
throttle.

Octane Index -

The evaluation of the octane number by the two laboratory methods requires a standard
engine, and the test procedure can be both expensive and time-consuming. The standard
engine required for the test may not always be available, especially in out-of-the-way places
or in small or mobile laboratories. These and other considerations led to the search for a
rapid method for the evaluation of the anti-knock quality of gasoline. Such methods include
FTIR, near infrared on-line analysers and others. Deriving an equation that can be used for
calculating the octane quality would also serve the same purpose with added advantages.
The term Octane Index is often used to refer to the calculated octane quality in
contradistinction to the (measured) research or motor octane numbers. The octane index
can be of great service in the blending of gasoline. Motor gasoline, as marketed, is usually a
blend of several types of refinery grades that are derived from different processes such as
straight-run gasoline, reformate, cracked gasoline etc. These different grades are considered
as one group when blending to meet final product specifications. Most refiners produce and
market more than one grade of motor gasoline, differing principally in their anti-knock
quality. The ability to predict the octane quality of the blends prior to blending is essential,
something for which the calculated octane index is specially suited.

6.10.4 Cetane number:-

Cetane number (cetane rating) is an indicator of the combustion speed of diesel
fuel and compression needed for ignition. It plays a similar role for diesel as octane rating
does for gasoline. The CN is an important factor in determining the quality of diesel fuel,
but not the only one; other measurements of diesel fuel's quality include (but are not
limited to) energy content, density, lubricity, cold-flow properties and sulphur content.

Definition:

The percentage and volume of cetane in a mixture of cetane and alpha methyl
naphthalene which just matches the knocking characteristics of diesel oil under test.
Oils having high cetane no. are good diesel fuels but are poor gasoline fuels and vice versa.

Typical values:

Generally, diesel engines operate well with a CN from 48 to 50. Fuels with lower cetane
number have longer ignition delays, requiring more time for the fuel combustion process
to be completed. Hence, higher speed diesel engines operate more effectively with higher
cetane number fuels.

In Europe,
diesel cetane numbers were set at a minimum of 38 in 1994 and 40 in 2000. The current
standard for diesel sold in European Union, Iceland, Norway and Switzerland is set in EN
590, with a minimum cetane index of 46 and a minimum cetane number of 51. Premium
diesel fuel can have a cetane number as high as 60.

In North America, most states adopt ASTM D975 as their diesel fuel standard and the
minimum cetane number is set at 40, with typical values in the 42-45 range. Premium
diesels may or may not have higher cetane, depending on the supplier. Premium diesel
often use additives to improve CN and lubricity, detergents to clean the fuel injectors and
minimize carbon deposits, water dispersants, and other additives depending on
geographical and seasonal needs.[citation needed]. California diesel fuel has a minimum
cetane of 53.

Alternative fuels:

Biodiesel from vegetable oil sources have been recorded as having a cetane number range
of 46 to 52, and animal-fat based biodiesels cetane numbers range from 56 to 60. Dimethyl
ether is a potential diesel fuel as it has a high cetane rating (55-60) and can be produced as
a biofuel. Most simple ethers, including liquid ones, such as diethyl ether can be used as
diesel fuels, although the lubricity can be of concern.

Chemical relevance:

Cetane is the chemical compound with chemical formula n-C16H34, today named
hexadecane according to IUPAC rules. It is an unbranched alkane, a saturated
hydrocarbon chain with no cycles. Cetane ignites very easily under compression, so it
was assigned a cetane number of 100, while alpha-methyl naphthalene was assigned a
cetane number of 0. All other hydrocarbons in diesel fuel are indexed to cetane as to
how well they ignite under compression. The cetane number therefore measures how
quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there
are hundreds of components in diesel fuel, with each having a different cetane quality,
the overall cetane number of the diesel is the average cetane quality of all the
components (strictly speaking high-cetane components will have disproportionate
influence, hence the use of high-cetane additives).

Measuring cetane number:

Accurate measurements of the cetane number are rather difficult, as it requires burning the
fuel in a rare diesel engine called a Cooperative Fuel Research (CFR) engine, under standard
test conditions. The operator of the CFR engine uses a hand-wheel to increase the
compression ratio (and therefore the peak pressure within the cylinder) of the engine until
the time between fuel injection and ignition is 2.407ms. The resulting cetane number is
then calculated by determining which mixture of cetane (hexadecane) and isocetane
(2,2,4,4,6,8,8-heptamethylnonane) will result in the same ignition delay.

Ignition Quality Tester (IQT) -

Another reliable method of measuring the derived cetane number (DCN) of diesel fuel is the
Ignition Quality Tester (IQT). This instrument applies a simpler, more robust approach to CN
measurement than the CFR. Fuel is injected into a constant volume combustion chamber at
approximately 575 °C and 310 psi. The time between the start of injection and the recovery
of the combustion chamber pressure to 310 psi is defined as the ignition delay. This
measured ignition delay is then used to calculate the DCN of the fuel. The fuel's DCN is then
calculated using an empirical inverse relationship to ignition delay. Because of the
reproducibility, material cost, and speed of the IQT, this has been the definitive source for
DCN measurements of fuels since the late 2000s.

Fuel ignition tester:

Another reliable method of measuring the derived cetane number of diesel fuel is the Fuel
Ignition Tester (FIT). This instrument applies a simpler, more robust approach to CN
measurement than the CFR. Fuel is injected into a constant volume combustion chamber in
which the ambient temperature is approximately 575 °C. The fuel combusts, and the high
rate of pressure change within the chamber defines the start of combustion. The ignition
delay of the fuel can then be calculated as the time difference between the start of fuel
injection and the start of combustion. The fuel's derived cetane number can then be
calculated using an empirical inverse relationship to ignition delay.

Cetane index -

Another method that fuel-users control quality is by using the cetane index (CI), which is a
calculated number based on the density and distillation range of the fuel. There are various
versions of this, depending on whether metric or Imperial units are used, and how many
distillation points are used. These days most oil companies use the '4-point method', ASTM

D4737, based on density, 10% 50% and 90% recovery temperatures. The '2-point method' is
defined in ASTM D976, and uses just density and the 50% recovery temperature. This
2-point method tends to overestimate cetane index and is not recommended. Cetane
index calculations cannot account for cetane improver additives and therefore do not
measure total cetane number for adultized diesel fuels. Diesel engine operation is
primarily related to the actual cetane number and the cetane index is simply an
estimation of the base cetane number.

6.10.5 Anti-knocking reagents -

An antiknock agent is a gasoline additive used to reduce engine knocking and
increase the fuel's octane rating by raising the temperature and pressure at which auto-
ignition occurs.

The mixture known as gasoline or petrol, when used in high compression internal

combustion engines, has a tendency to knock (also called "pinging" or "pinking")

and/or to ignite early before the correctly timed spark occurs (pre-ignition, refer to
engine knocking).

Research:

Early research into this effect was led by A.H. Gibson and Harry Ricardo in England and
Thomas Midgley, Jr. and Thomas Boyd in the United States. The discovery that lead
additives modified this behavior led to the widespread adoption of the practice in the 1920s
and therefore more powerful higher compression engines. The most popular additive was
tetraethyllead. However, with the discovery of the environmental and health damage
caused by the lead, attributed to Derek Bryce-Smith and Clair Cameron Patterson, and the
incompatibility of lead with catalytic converters found on virtually all US automobiles since
1975, this practice began to wane in the 1980s. Most countries are phasing out leaded fuel
although different additives still contain lead compounds. Other additives include aromatic
hydrocarbons, ethers and alcohol (usually ethanol or methanol).

Typical agents:

The typical antiknock agents in use are:

Tetraethyllead (still in use as a high octane additive)
Alcohol
Methylcyclopentadienyl manganese tricarbonyl (MMT)
Ferrocene
Iron pentacarbonyl
Toluene
Isooctane

BTEX - a hydrocarbon mixture of benzene, toluene, xylene and ethyl-benzene, also
called gasoline aromatics

6.10.6 Unleaded petrol:-

1. unleaded petrol - gasoline that has not been treated with a lead compound.
unleaded gasoline. gasolene, gasoline, petrol, gas - a volatile flammable mixture of
hydrocarbons (hexane and heptane and octane etc.) derived from petroleum; used mainly
as
a fuel in internal-combustion engines.

Oxygenates -

Oxygenated chemical compounds contain oxygen as a part of their chemical
structure. The term usually refers to oxygenated chemical compounds added to fuels.
Oxygenates are usually employed as gasoline additives to reduce carbon monoxide and
soot that is created during the burning of the fuel. Compounds related to soot, such as
polyaromatic hydrocarbons (PAHs) and nitrated PAHs, are also reduced.
The oxygenates commonly used are either alcohols or ethers:
Alcohols:
Methanol (MeOH)
Ethanol (EtOH); see also Common ethanol fuel mixtures
Isopropyl alcohol (IPA)
n-Butanol (BuOH)
Gasoline grade tert-butanol (GTBA)
Ethers:
Methyl tert-butyl ether (MTBE)

tert-Amyl methyl ether (TAME)

tert-Hexyl methyl ether (THEME)
Ethyl tert-butyl ether (ETBE)
tert-Amyl ethyl ether (TAEE)
Diisopropyl ether (DIPE)

Here is a small quiz: (Ans. D)
(Ans. B)
(1) Fuel injector is used in : (Ans. C)
(a) steam engines (Ans. B)
(b) gas engines (Ans. A)
(c ) spark iginition engines
(d) compression iginition engines

(2) Compression ratio for diesel engine may have a range of
(a) 8 to 10
(b) 16 to 30
(c )10 to 15
(d) None of the these

(3) The function of fuel injector is to –
(a) Pump the fuel at high pressure
(b)Mix diesel with air
(c )Atmoise the fuel
(d)Ignite the fuel

(4) Anti-knock property of C.I. engine fuel can be improved by adding
(a) Tetra-ethyl lead
(b)Amy nitrate
(c )Hexadecane
(d) Trimethyl pentane

(5) The knocking tendency in C.I. engines increase with
(a) decrease of compression ratio
(b)increase of compression ratio
(c )increasing the temperature of inlet air
(d)increasing cooling water temperature

6.10.7 Catalytic converter:-

A catalytic converter is an exhaust emission control device that reduces toxic gases
and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants
by catalysing a redox reaction (an oxidation and a reduction reaction). Catalytic converters
are usually used with internal combustion engines fuelled by either gasoline or diesel—
including lean-burn engines as well as kerosene heaters and stoves.
The first widespread introduction of catalytic converters was in the United States
automobile market. To comply with the U.S. Environmental Protection Agency's stricter
regulation of exhaust emissions, most gasoline-powered vehicles starting with the 1975
model year must

be equipped with catalytic converters.These "two-way" converters combine oxygen with
carbon monoxide (CO) and unburned hydrocarbons (C H ) to produce carbon dioxide
(CO2) and water (H2O). In 1981, two-way catalytic converters were rendered obsolete
by "three-way" converters that also reduce oxides of nitrogen (NO
x); however, two-way converters are still used for lean-burn engines. This is because three-
way-converters require either rich or stoichiometric combustion to successfully reduce NO

x.

Although catalytic converters are most commonly applied to exhaust systems in
automobiles, they are also used on electrical generators, forklifts, mining equipment,
trucks, buses, locomotives, and motorcycles. They are also used on some wood stoves to
control emissions. This is usually in response to government regulation, either through
direct environmental regulation or through health and safety regulations.

History:

Catalytic converter prototypes were first designed in France at the end of the 19th century,
when only a few thousand "oil cars" were on the roads; it was constituted of an inert
material coated with platinum, iridium, and palladium, sealed into a double metallic
cylinder.

A few decades later, a catalytic converter was patented by Eugene Houdry, a French
mechanical engineer and expert in catalytic oil refining, who moved to the United States
in 1930. When the results of early studies of smog in Los Angeles were published, Houdry
became concerned about the role of smokestack exhaust and automobile exhaust in air
pollution and founded a company called Oxy-Catalyst. Houdry first developed catalytic
converters for smokestacks called "cats" for short, and later developed catalytic
converters for warehouse forklifts that used low grade, unleaded gasoline.[8] In the mid-
1950s, he began research to develop catalytic converters for gasoline engines used on
cars. He was awarded United States Patent 2,742,437 for his work.

Widespread adoption of catalytic converters did not occur until more stringent emission
control regulations forced the removal of the antiknock agent tetraethyl lead from most
types of gasoline. Lead is a catalyst poison and would effectively disable a catalytic
converter by forming a coating on the catalyst's surface.

Catalytic converters were further developed by a series of engineers including Carl D. Keith,
John J. Mooney, Antonio Eleazar, and Phillip Messina at Engelhard Corporation, creating
the first production catalytic converter in 1973.

William C. Pfefferle developed a catalytic combustor for gas turbines in the early 1970s,
allowing combustion without significant formation of nitrogen oxides and carbon
monoxide.

Construction:

The catalyst support or substrate. For automotive catalytic converters, the core is usually a
ceramic monolith that has a honeycomb structure (commonly square, not hexagonal).
(Prior to the mid 1980s, the catalyst material was deposited on a packed bed of pellets,
especially in early GM applications.) Metallic foil monoliths made of Kanthal (FeCrAl) are
used in applications where particularly high heat resistance is required. The substrate is
structured to produce a large surface area. The cordierite ceramic substrate used in most
catalytic converters was invented by Rodney Bagley, Irwin Lachman, and Ronald Lewis at
Corning Glass, for which they were inducted into the National Inventors Hall of Fame in
2002.
The washcoat. A washcoat is a carrier for the catalytic materials and is used to disperse the
materials over a large surface area. Aluminum oxide, titanium dioxide, silicon dioxide, or a
mixture of silica and alumina can be used. The catalytic materials are suspended in the
washcoat prior to applying to the core. Washcoat materials are selected to form a rough,
irregular surface, which greatly increases the surface area compared to the smooth surface
of the bare substrate. This in turn maximizes the catalytically active surface available to
react with the engine exhaust. The coat must retain its surface area and prevent sintering of
the catalytic metal particles even at high temperatures (1000 °C).
Ceria or ceria-zirconia. These oxides are mainly added as oxygen storage promoters.
The catalyst itself is most often a mix of precious metal. Platinum is the most active
catalyst and is widely used, but is not suitable for all applications because of unwanted
additional reactions and high cost. Palladium and rhodium are two other precious metals
used. Rhodium is used as a reduction catalyst, palladium is used as an oxidation catalyst,
and platinum is used both for reduction and oxidation. Cerium, iron, manganese, and
nickel are also used, although each has limitations. Nickel is not legal for use in the
European Union because of its reaction with carbon monoxide into toxic nickel
tetracarbonyl. Copper can be used everywhere except Japan.
Upon failure, a catalytic converter can be recycled into scrap. The precious metals inside the
converter, including platinum, palladium, and rhodium, are extracted.

Placement of catalytic converters:

Catalytic converters require a temperature of 800 degrees Fahrenheit (426 °C) to
efficiently convert harmful exhaust gases into inert gases, such as carbon dioxide and
water vapor. Therefore, the first catalytic converters were placed close to the engine, to

ensure fast heating. However, such placement can cause several problems. One of these is
vapor lock.

As an alternative, catalytic converters were moved to a third of the way back from
the engine, and were then placed underneath the vehicle.

Types -

Two-way:

A 2-way (or "oxidation", sometimes called an "oxi-cat") catalytic converter has
two simultaneous tasks:

Oxidation of carbon monoxide to carbon dioxide: 2 CO + O2 → 2 CO2

Oxidation of hydrocarbons (unburnt and partially burned fuel) to carbon dioxide and water:
CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O (a combustion reaction)

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon
and carbon monoxide emissions. They were also used on gasoline engines in American-
and Canadian-market automobiles until 1981. Because of their inability to control oxides
of nitrogen, they were superseded by three-way converters.

Three-way:

Three-way catalytic converters (TWC) have the additional advantage of controlling the
emission of nitric oxide (NO) and nitrogen dioxide (NO2) (both together abbreviated with
NO x and not to be confused with nitrous oxide (N2O)), which are precursors to acid rain and
smog.

Since 1981, "three-way" (oxidation-reduction) catalytic converters have been used in vehicle
emission control systems in the United States and Canada; many other countries have also
adopted stringent vehicle emission regulations that in effect require three-way converters on
gasoline-powered vehicles. The reduction and oxidation catalysts are typically contained in a
common housing; however, in some instances, they may be housed separately. A three-way
catalytic converter has three simultaneous tasks:

Reduction of nitrogen oxides to nitrogen (N2)

2CO+2NO→2CO2+N2
hydrocarbon + NO → CO2 + H2O + N2

2H2+2NO→2H2O+N2
Oxidation of carbon monoxide to carbon dioxide

2CO+O2→2CO2
Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water, in addition to
the above NO reaction

hydrocarbon + O2 → H2O + CO2
These three reactions occur most efficiently when the catalytic converter receives exhaust
from an engine running slightly above the stoichiometric point. For gasoline combustion,
this ratio is between 14.6 and 14.8 parts air to one part fuel, by weight. The ratio for
autogas (or liquefied petroleum gas LPG), natural gas, and ethanol fuels can be significantly
different for each, notably so with oxygenated or alcohol based fuels, with e85 requiring
approximately 34% more fuel to reach stoic, requiring modified fuel system tuning and
components when using those fuels. In general, engines fitted with 3-way catalytic
converters are equipped with a computerized closed-loop feedback fuel injection system
using one or more oxygen sensors,[citation needed] though early in the deployment of
three-way converters, carburetors equipped with feedback mixture control were used.

Three-way converters are effective when the engine is operated within a narrow band of
air-fuel ratios near the stoichiometric point, such that the exhaust gas composition
oscillates between rich (excess fuel) and lean (excess oxygen). Conversion efficiency falls
very rapidly when the engine is operated outside of this band. Under lean engine operation,
the exhaust contains excess oxygen, and the reduction of NO x is not favored. Under rich
conditions, the excess fuel consumes all of the available oxygen prior to the catalyst, leaving
only oxygen stored in the catalyst available for the oxidation function.

Closed-loop engine control systems are necessary for effective operation of three-
way catalytic converters because of the continuous balancing required for effective
NO x reduction and HC oxidation. The control system must prevent the NO
x reduction catalyst from becoming fully oxidized, yet replenish the oxygen storage
material so that its function as an oxidation catalyst is maintained.

Three-way catalytic converters can store oxygen from the exhaust gas stream, usually when
the air–fuel ratio goes lean.[19] When sufficient oxygen is not available from the exhaust
stream, the stored oxygen is released and consumed (see cerium(IV) oxide). A lack of
sufficient oxygen occurs either when oxygen derived from NO
x reduction is unavailable or when certain maneuvers such as hard acceleration enrich
the mixture beyond the ability of the converter to supply oxygen.

Unwanted reactions:

Unwanted reactions can occur in the three-way catalyst, such as the formation of
odoriferous hydrogen sulfide and ammonia. Formation of each can be limited by
modifications to the washcoat and precious metals used. It is difficult to eliminate these
byproducts entirely. Sulfur-free or low-sulfur fuels eliminate or reduce hydrogen sulfide.

For example, when control of hydrogen-sulfide emissions is desired, nickel or manganese is
added to the washcoat. Both substances act to block the absorption of sulfur by the
washcoat. Hydrogen sulfide forms when the washcoat has absorbed sulfur during a low-
temperature part of the operating cycle, which is then released during the high-
temperature part of the cycle and the sulfur combines with HC.

Diesel engines -

For compression-ignition (i.e., diesel) engines, the most commonly used catalytic
converter is the diesel oxidation catalyst (DOC). DOCs contain palladium, platinum, and
aluminium oxide, all of which catalytically oxidize the hydrocarbons and carbon monoxide
with oxygen to form carbon dioxide and water.

2CO+O2→2CO2
CxH2x+2 + [(3x+1)/2] O2 → x CO2 + (x+1) H2O
These converters often operate at 90 percent efficiency, virtually eliminating diesel odor
and helping reduce visible particulates (soot). These catalysts do not reduce NO
x because any reductant present would react first with the high concentration of O2 in
diesel exhaust gas.

Reduction in NO x emissions from compression-ignition engines has previously been
addressed by the addition of exhaust gas to incoming air charge, known as exhaust gas
recirculation (EGR).

Environmental impact -

Catalytic converters have proven to be reliable and effective in reducing noxious
tailpipe emissions. However, they also have some shortcomings in use, and also
adverse environmental impacts in production:

An engine equipped with a three-way catalyst must run at the stoichiometric point,
which means more fuel is consumed than in a lean-burn engine. This means
approximately 10% more CO2 emissions from the vehicle.

Catalytic converter production requires palladium or platinum; part of the world supply of
these precious metals is produced near Norilsk, Russia, where the industry (among others)
has caused Norilsk to be added to Time magazine's list of most-polluted places.
Pieces of catalytic converters, and the extreme heat of the converters themselves, can
cause wildfires, especially in dry areas.
Theft Because of the external location and the use of valuable precious metals including
platinum, palladium and rhodium, catalytic converters are a target for thieves. The problem
is especially common among late-model trucks and SUVs, because of their high ground
clearance and easily removed bolt-on catalytic converters. Welded-on converters are also
at risk of theft, as they can be easily cut off. Pipecutters are often used to quietly remove
the converter, but other tools such as a portable reciprocating saw can often damage other
components of the car, such as the alternator, wiring or fuel lines, thus, there are
dangerous consequences. Rising metal prices in the U.S. during the 2000s commodities
boom led to a significant increase in converter theft, and unfortunately a catalytic
converter can cost more than $1,000 to replace. This amount increases (sometimes greatly)
if further damage was done to the vehicle in the process of removing the converter.

6.11 Theory for solving problems on combustions:

1) Air contains 23% oxygen by weight and 21% oxygen by volume.
2) At NTP 22.4 m3 of any of gas will weigh 1 kg of molecule.
3) Average molecular weight of sample is 28.94.

Analysis of fuel sample –

1] If composition is given by weight –

• From analysis of fuel sample, we get the following information –
Fuel sample contains

C = x1%, H = x2%, O = x3%, S = x4%, N = x5%, Ash = x6%
• We are required to find the minimum quantity of air needed for complete

combustion of 1kg of fuel.
• We do our analysis on 1kg of fuel and then convert the data found for 1kg of fuel to

x kg of fuel.

Steps to solve –

1) Convert the % composition of each constituent of fuel into their respective weights
present in 1 kg of fuel as follows –
C = x1/100 kg, H = x2/100 kg, O = x3/100 kg, S = x4/100 kg, N = x5/100 kg, Ash = x6/100
kg.

2) Out of all the constituents we only take into consideration amount of oxygen
required for combustion of C, H, S.

3) Write down combustion reaction for C, H, and S as follows and analyze the amount
of oxygen required for combustion of given sample of fuel.
Reaction –

• C + O2 → CO2
12kg 32kg
i.e. 12 kg of carbon requires 32 kg of oxygen for combustion so the amount of
oxygen required for combustion of x1/100 kg of carbon is –

(x1/100) × (32/12) kg of oxygen required

• H2 + ½ O2 → H2O
2kg 16kg
i.e. 2kg of hydrogen requires 16 kg of oxygen for combustion so the amount of
oxygen required for combustion of x2/100 kg of hydrogen is –

(x2/100) × (16/2) kg of oxygen required

• S + O2 → SO2
32kg 32 kg
i.e. 32kg of sulphur requires 32 kg of oxygen for combustion so the amount of
oxygen required for combustion of x3/100 kg of sulphur is –

(x3/100) × (32/32) kg of oxygen required

4) Add the amount of oxygen required for combustion of C, H and S to find amount of
oxygen required for combustion of fuel cell is x7,

X7 = [(x1/100)×(32/12)] + [(x2/100)×(16/2)] + [(x3/100)×(32/32)] kg

5) It may happen that fuel sample already has certain amount of oxygen present so to
find actual amount of oxygen required for combustion we must subtract the amount
of oxygen initially present in the fuel let the actual amount of oxygen required be x8,

X8 = (x7 – x3/100)

Note: - If in the question while giving the composition of fuel the amount of oxygen
present in the fuel is not mentioned then we assume it to be zero (i.e. x3 =0%) and
solve the problem in this case x8 = x7.

6) Now we know that air contains 23 % oxygen by weight. This means that 1kg of air
has 0.23 kg of oxygen. So, the amount of air that will contain x8 kg of oxygen is as
follows –

Amount of air (x9) = (x8/0.23) kg

7) Now we have amount of air required for combustion of 1 kg of fuel. So, the amount
of air required for combustion of x kg of fuel is as follows –

Amount of air (x10) = (x × x9) kg

Therefore, the amount of air required for complete combustion of x kg of fuel is x10
(kg).

2] If composition is given by volume –

• From analysis of fuel sample, we get the following information –
Fuel sample contains –
H = x1%, CO = x2%, CH4 = x3%, N = x4%, water vapor = x5%, oxygen = x6%

• We are needed to find out the minimum quantity of air required for complete
combustion of x m3 of fuel.

• We do our analysis on 1 m3 fuel and then convert the data of 1 m3 furl into x m3 of
fuel.

Steps to solve –

1) Convert the %composition of each constituent of fuel into the respective volumes
present in 1 m3 cube of fuel as follows –
H = x1/100 m3, CO = x2/100 m3, CH4 = x3/100 m3, N = x4/100 m3,
water vapor = x5/100 m3, oxygen = x6/100 m3.

2) Out of all the consideration we only take into consideration the amount of oxygen
required for combustion of H, CO and any hydrocarbon present in the fuel.

3) Write down the combustion reactions for H, CO and any hydrocarbon present in the

fuel and analyze the amount of oxygen required for combustion of given sample of
fuel.
Reaction –
• H2 + ½ O2 → H2O
1m3 ½ m3
i.e. 1m3 of H2 requires 0.5 m3 of oxygen for combustion so the amount of oxygen
required for combustion of x1/100 m3 of hydrogen is

(x1/100) × (0.5) m3 of oxygen required

• CO + ½ O2 → CO2
1m3 0.5m3
3oxygen required for combustion of x2/100 m3 of CO is

(x2/100) × (0.5) m3 of oxygen required

• CH4 + 2O2 → 2H2O
1m3 2m3

i.e. 1m3 of CH4 requires 2m3 oxygen for combustion so the amount of oxygen
required for combustion of x3/100 m3 of CH4 is

(x3/100) × (2) m3 of oxygen required

Note : - If the fuel contains any other hydrocarbon write the combustion
Reaction for that hydrocarbon and find the amount of oxygen required for its
Combustion.

4) Add the amount of oxygen required for the combustion of H, CO and all the
hydrocarbons present in the fuel sample to find the amount of oxygen required for
combustion of fuel (x7) –

X7 = [(x1/100)×(0.5)] + [(x2/100)×(0.5)] + [(x3/100)×(2)] m3 of oxygen

5) It may happen that fuel sample already has certain amount of oxygen present so to
find actual amount of oxygen required for combustion we must subtract the amount
of oxygen initially present in the fuel let the actual amount of oxygen required be x8,

Actual amount of oxygen = (x7 – x6/100)
required(x8)

Note :- If in the question while giving the composition of fuel the amount of oxygen
present in the fuel is not mentioned then we assume it to be zero (i.e. x7 = 0%) and
solve the problem in this case x8 = x7.

6) Now we know that air contains 21% oxygen by volume. This means that 1m3 of air
contains 0.21m3 of oxygen. So, the amount of air that will contain x8 m3
of fuel as follows –

amount of air (x9) = (x8/0.21) m3 of oxygen

7) Now we have amount of air required for combustion of 1m3 of fuel. So, the amount
of air required for combustion of x m3 of fuel as follows –

Amount of air (x10) = (x × x9) m3 of air
Therefore, amount of air required for combustion of x m3 of fuel is x10 m3.

6.12 SUMMARY

Fuels and combustion is one of the most important chapter according to our day
to day life. Fuels has its base from 1858, where it was discovered by Edwin Drake.
Fuels are considered to be important part of our life. We need fuels in one or
other way for example cooking, lightning, travelling and etc. In this chapter we
read about the history of fuel it’s characteristics and different types of fuels like
solid, liquid and gaseous. The aim of this chapter was to get clear the concept of
fuels and combustion, like the calorific value, different analysis of fuels, refining of
petroleum and many more. Combustion of fuels is also an important concept
because here we come to know the amount of oxygen required for the burning of
coal samples and etc. We also read about types fuels, mainly solid and liquid fuels.
In solid fuels we have seen coal as it is the most important fuel in daily life, coal is
used from household needs to industrial needs, therefore it was important for us
to know what a good coal and to know this we read about the analysis of coal.
There are two types – Proximate and Ultimate analysis, by which we got clear
about the units of coal like % carbon, % nitrogen, %ash and many more things.
In liquid fuels we read about petroleum, gasoline etc. We also read about the
refining of crude oil which is one of the most important concepts of fuels.
Now a days there are mainly two type of engines petrol engine and diesel engine,
And with this we also came to know about knocking and anti-knocking.
Conservation of fuels is one of the important topic, cause there is less availability
of fuels for our coming generation, we need to learn to use our fuels without
wasting it cause in coming years there will be shortage of fossil fuels. So this
chapter explained most of thing like the industrial use of coal, and the working of

stroke engines and the construction and working of catalytic converter and many
more topics.

6.13 QUESITIONS

6.13.1 Short Answer the Following-

1. Define octane and cetane number with an example.

2. Write a short note on unleaded petrol.

3. Give 4 examples of anti-knocking agents.

4. Select the compound which posses highest octane number and cetane number out
of –

n-heptane

iso-octane

n-octane

5. What is the octane number of the petrol and cetane number of the diesel currently in
use.

6. which is the anti-knocking agent added in petrol in India

6.13.2 Long answer type question –

1. What are fuels? How are they classified?

2. Explain the term calorific value and ignition temperature.

3. Explain how proximate analysis is conducted and tell it’s significance.

4. Explain the types of liquid fuels.

5. Write a note on process of knocking with an example.

6. Explain 4-stroke diesel engine.

6.13.3 Numerical: -

1. Calculate the gross and net calorific value of a coal which analyses: C 74%, H
6%, N 1%, O 9%, S 0.8%, moisture 2.2% and ash 8%.

Sol: GCV = 339×%C + 1427(%H −
%O/8) + 22×%S

= 32060.2 KJ/Kg
NCV = GCV – 24.44(9×%H + %M)

= 30630.26 KJ/Kg

Thus NCV = 0.955 times GCV in this case

Try this unsolved question :-

Q1] The ultimate analysis of a coal(moist basis in %): C 69.8 , H 4.6 , N 1.4, O 8.5, S
2.5, H2O 4.5 and ash 8.7. The gross calorific value, moist basis, is 29920 KJ/Kg.
Calculate, by means of the Dulong formula, the gross calorific value, moist basis,
of the coal.

(GCV=28765.2KJ/Kg)

Q2] A producer gas analyses 50% N2, 25% CO, 18% H2, 6% CO2 and 1% O2.
Calculate net calorific power (Kcal/m3).
(NCV = 5210 KJ/m3)

Q3] 1.5g of coal sample was analysed for nitrogen content in kjeldalh’s method.
Liberated ammonia required 14ml of 0.1N H2SO4 for neutralisation. In separate
experiment 1.5g of same sample gave 0.3g of BaSO4 . Calculate the % of nitrogen
and sulphur in given sample.
(%N = 1.31% and %S = 2.746%)

Q4] A coal sample was analysed as follows 25g of coal was weighed into silica
crucible after heating for 1 hr at 1100C the residue weighed 2.41gm. the crucible
next covered with a vented lid and strongly heated for 7 min at 950+/-200C the
residue weighed 1.528 gm. The crucible was then heated without cover at 700oC
until the coal was completely burnt and the weight of residue was 0.245 gm.
Calculate the result of proximate analysis.
(%moisture = 3.4% %VM = 35.28% %Ash = 9.8% %C = 51.32%)

Q5] An air-dried sample of coal weighing 2.9gm was taken for volatile matter
determined. After losing volatile matter the coal sample weighed 1.96gm if the
sample contains 4.5% of moisture find the % of VM.
(W2 = 20.88 gm W1 = 2.769gm %moisture = 27.89%)

Q6] 1.4g of sample in kjeldahl’s estimation liberated NH3 which was absorbed in
50ml of 0.1N H2SO4. The resultant solution required 10ml of 0.1N NaOH solution
for complete neutralization. Find % of nitrogen.
(%N = 4%)

Q7] A coal sample was subjected to ultimate analysis –
0.5g of coal produced 1.45gm of CO2 and 0.225gm of H2O. 0.4g of coal in
kjeldahl’s estimation produced NH3 which on passing in 50ml of 0.5N of H2SO4
was neutralised by 44ml of 0.5N NaOH. 0.5g of coal on combustion in bomb

calorimeter reacted with BaCl2 to produce 0.04g BaSO4. Calculate GCV and NCV if
he coal contains 3.5% of ash.
(%C = 79.0909% %H = 5% %S = 1.0987% %N = 10.57%
%O = 0.8104% GCV = 8105.2071cal/gm NCV = 7841.0571 cal/gm)

Q8] An air-dried sample of coal weighing 2.9gm was taken for VM determination.
After loosing VM, the coal sample weighed 1.96gm. If the sample contains 4.5% of
moisture. Find % of VM.
(w1 = 2.7695g %VM = 27.9138%)

Q9] Analysis of sample of coal gave the following information C = 80%, H = 5%, O =
8%, S = 2.6%, and ash = 4.4%. Calculate the minimum quantity of air needed for
complete combustion of 1 kg of coal.
(min quantity of air required is 10.778 kg)

Q10] A sample of coal was found to contain C = 80%, H = 6%, N = 3.5%
S = 5%, ash = 4.5 % and remaining is O2. Calculate the minimum weight of air
required for complete combustion of 2kg of coal.
(min quantity of air required is 23.0726 kg)

Q11] Calculate the volume of air required for 1m3 of gaseous fuel having following
composition by volume H = 50%, CO = 8%, CH4 = 3.2%
N = 6%, and water vapour = 2.5%.
(min quantity of air required is 4.42m3)

Q12] A gaseous fuel has following composition by volume CH4 = 42%, H = 10%,
C2H4 = 15%, O = 5%. Calculate the volume of air required for combustion of 1m3 of
fuel.
(volume air required is 6.3095 m3)

Q13] Calculate weight and volume of air required for complete combustion of 1kg
of coal containing C = 66%, H = 5.5%, O = 8%,
N = 2.8%, and moisture = 14.5%.
(weight of air required is 9.2174kg
Volume of air required is 7.1344m3)

Q14] A gaseous fuel has following composition by volume H2 = 40%, CH4 = 20%,
C2H6 = 20%, CO = 5%, O2 = 3%. Calculate the weight and volume of air required
per m3 of this fuel.
(weight of air req. = 7.9692 kg vol of air req. = 6.1667m3)

Q15] Calculate the weight and volume of gaseous fuel having following
composition by volume CH4 = 40%, C2H8 = 16%, CO2 = 5%,
CO = 5%, H = 7%, O2 = 3%. Calculate weight of air supplied per m3 of this gas at
NTP assuming 50% excess of that theoretically required air was used.
(vol of air required is 11.6429m3 weight of air req. = 15.0422 kg)

Q16] Calculate the weight and volume of air required for combustion of 3kg of
carbon.
(air by weight req. = 34.7826 kg air by vol req. = 26.922m3)

6.14 REFERENCES –

https://www.sciencedirect.com/topics/chemistry/calorific-value
https://brainly.in/question/1220737
https://www.sanfoundry.com/applied-chemistry-questions-answers-dullongs-
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https://www.thoughtco.com/what-is-lignite-1182547

https://www.britannica.com/science/bituminous-coal

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https://www.thoughtco.com/what-is-anthracite-coal-1182544

https://www.reference.com/science/petrol-engine-work-d269f6657d0a9b8c

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https://carbiketech.com/diesel-engine/
http://www.petroleum.co.uk/refining