Chapter-1

Introduction

A diesel engine (also known as a compression-ignition engine) is an internal combustion

engine that uses the heat of compression to initiate ignition and burn the fuel that has been
injected into the combustion chamber. This contrasts with spark-ignition engines such as
a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline),
which use a spark plug to ignite an air-fuel mixture.

The diesel engine has the highest thermal efficiency of any standard internal or external
combustion engine due to its very high compression ratio. Low-speed diesel engines (as used
in ships and other applications where overall engine weight is relatively unimportant) can have
a thermal efficiency that exceeds 50%.

Diesel engines are manufactured in two-stroke and four-stroke versions. They were originally
used as a more efficient replacement for stationary steam engines. Since the 1910s they have
been used in submarines and ships. Use in locomotives, trucks, heavy equipment and electric
generating plants followed later. In the 1930s, they slowly began to be used in a
few automobiles. Since the 1970s, the use of diesel engines in larger on-road and off-road
vehicles in the USA increased. According to the British Society of Motor Manufacturing and
Traders, the EU average for diesel cars account for 50% of the total sold, including 70% in
France and 38% in the UK.

The world's largest diesel engine is currently a Wärtsilä-Sulzer RTA96-C Common Rail
marine diesel of about 84,420 kW (113,210 hp) @ 102 rpm output.
1.1 History

In 1885, the English inventor Herbert Akroyd Stuart began investigating the possibility of
using paraffin oil (very similar to modern-day diesel) for an engine, which unlike petrol would
be difficult to be vaporised in a carburettor as its volatility is not sufficient to allow this.

His engines, built from 1891 by Richard Hornsby and Sons, were the first internal combustion
engine to use a pressurised fuel injection system. The Hornsby-Akroyd engine used a
comparatively low compression ratio, so that the temperature of the air compressed in the
combustion chamber at the end of the compression stroke was not high enough to initiate
combustion. Combustion instead took place in a separated combustion chamber, the
"vaporizer" (also called the "hot bulb") mounted on the cylinder head, into which fuel was
sprayed. Self-ignition occurred from contact between the fuel-air mixture and the hot walls of
the vaporizer. As the engine's load increased, so did the temperature of the bulb, causing the
ignition period to advance; to counteract pre-ignition, water was dripped into the air intake.
The modern Diesel engine incorporates the features of direct (airless) injection and
compression-ignition. Both ideas were patented by Akroyd Stuart and Charles Richard Binney
in May 1890. Another patent was taken out on 8 October 1890, detailing the working of a
complete engine - essentially that of a diesel engine - where air and fuel are introduced
separately. The difference between the Akroyd engine and the modern Diesel engine was the
requirement to supply extra heat to the cylinder to start the engine from cold. By 1892, Akroyd
Stuart had produced an updated version of the engine that no longer required the additional
heat source, a year before Diesel's engine.

In 1892, Akroyd Stuart patented a water-jacketed vaporizer to allow compression ratios to be

increased. In the same year, Thomas Henry Barton at Hornsby’s built a working high-
compression version for experimental purposes, whereby the vaporizer was replaced with
a cylinder head, therefore not relying on air being preheated, but by combustion through
higher compression ratios. It ran for six hours - the first time automatic ignition was produced
by compression. This was five years before Rudolf Diesel built his well-known high-
compression prototype engine in 1897.

Rudolf Diesel was, however, subsequently credited with the innovation, and he was able to
improve the engine further, whereas Akroyd Stuart stopped development on his engine in 1893.

In 1892 he received patents in Germany, Switzerland, the United Kingdom and the United
States for "Method of and Apparatus for Converting Heat into Work".[13] In 1893 he described
a "slow-combustion engine" that first compressed air thereby raising its temperature above the
igniting-point of the fuel, then gradually introducing fuel while letting the mixture expand
"against resistance sufficiently to prevent an essential increase of temperature and pressure",
then cutting off fuel and "expanding without transfer of heat". In 1894 and 1895 he filed patents
and addenda in various countries for his Diesel engine; the first patents were issued in Spain
(No. 16,654), France (No. 243,531) and Belgium (No. 113,139) in December 1894, and in
Germany (No. 86,633) in 1895 and the United States (No. 608,845) in 1898. He operated his
first successful engine in 1897.

At Augsburg, on August 10, 1893, Rudolf Diesel's prime model, a single 10-foot (3.0 m) iron
cylinder with a flywheel at its base, ran on its own power for the first time. Diesel spent two
more years making improvements and in 1896 demonstrated another model with a theoretical
efficiency of 75%, in contrast to the 10% efficiency of the steam engine. By 1898, Diesel had
become a millionaire. His engines were used to power pipelines, electric and water plants,
automobiles and trucks, and marine craft. They were soon to be used in mines, oil fields,
factories, and transoceanic shipping.

1.2 How diesel engines work

P-V Diagram for the Ideal Diesel cycle. The cycle follows the numbers 1-4 in clockwise
direction. In the diesel cycle the combustion occurs at almost constant pressure and the exhaust
occurs at constant volume. On this diagram the work that is generated for each cycle
corresponds to the area within the loop.

The diesel internal combustion engine differs from the gasoline powered Otto cycle by using
highly compressed hot air to ignite the fuel rather than using a spark plug (compression
ignition rather than spark ignition).

In the true diesel engine, only air is initially introduced into the combustion chamber. The air
is then compressed with a compression ratio typically between 15:1 and 22:1 resulting in 40-
bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4 MPa; 120 to 200 psi) in
the petrol engine. This high compression heats the air to 550 °C (1,022 °F). At about the top of
the compression stroke, fuel is injected directly into the compressed air in the combustion
chamber. This may be into a (typically toroidal) void in the top of the piston or a pre-
chamber depending upon the design of the engine. The fuel injector ensures that the fuel is
broken down into small droplets, and that the fuel is distributed evenly. The heat of the
compressed air vaporizes fuel from the surface of the droplets. The vapors is then ignited by
the heat from the compressed air in the combustion chamber, the droplets continue to vaporize
from their surfaces and burn, getting smaller, until all the fuel in the droplets has been burnt.
The start of vaporization causes a delay period during ignition and the characteristic diesel
knocking sound as the vapors reaches ignition temperature and causes an abrupt increase in
pressure above the piston. The rapid expansion of combustion gases then drives the piston
downward, supplying power to the crankshaft.

As well as the high level of compression allowing combustion to take place without a separate
ignition system, a high compression ratio greatly increases the engine's efficiency. Increasing
the compression ratio in a spark-ignition engine where fuel and air are mixed before entry to
the cylinder is limited by the need to prevent damaging pre-ignition. Since only air is
compressed in a diesel engine, and fuel is not introduced into the cylinder until shortly before
top dead center (TDC), premature detonation is not an issue and compression ratios are much
higher.

1.3 Efficiency

Due to its high compression ratio, the Diesel engine has a high efficiency, and the lack of a
throttle valve means that the charge-exchange losses are fairly low, resulting in a low specific
fuel consumption, especially in medium and low load situations. This makes the Diesel engine
very economical.[132] Even though Diesel engines have a theoretical efficiency of 75%, in
practice it is much lower. In his 1893 essay Theory and Construction of a Rational Heat Motor,
Rudolf Diesel describes that the effective efficiency of the Diesel engine would be in between
43.2 % and 50.4 %, or maybe even greater.[134] Modern passenger car Diesel engines may have
an effective efficiency of up to 43 %, whilst engines in large Diesel trucks, and buses can
achieve peak efficiencies around 45%. However, average efficiency over a driving cycle is
lower than peak efficiency. For example, it might be 37% for an engine with a peak efficiency
of 44%. The highest Diesel engine efficiency of up to 55 % is achieved by large two-stroke
watercraft Diesel engines.

1.4 Mass

The average Diesel engine has a poorer power-to-mass ratio than the Otto engine. This is
because the Diesel must operate at lower engine speeds. Due to the higher operating pressure
inside the combustion chamber, which increases the forces on the parts due to inertial forces,
the Diesel engine needs heavier, stronger parts capable of resisting these forces, which results
in an overall greater engine mass.

1.5 Emissions

As Diesel engines burn a mixture of fuel and air, the exhaust therefore contains substances that
consist of the same chemical elements, as fuel and air. The main elements of air
are nitrogen (N2) and oxygen (O2), fuel consists of hydrogen (H2) and carbon (C). Burning the
fuel will result in the final stage of oxidation. An ideal Diesel engine, (a hypothetical model
that we use as an example), running on an ideal air-fuel mixture, produces an exhaust that
consists of carbon dioxide (CO2), water (H2O), nitrogen (N2), and the remaining oxygen(O2).
The combustion process in a real engine differs from an ideal engine's combustion process, and
due to incomplete combustion, the exhaust contains additional substances, most
notably, carbon monoxide (CO), Diesel particulate matter (PM), and due
to dissociation, nitrogen oxide (NOx).
When Diesel engines burn their fuel with high oxygen levels, this results in high combustion
temperatures and higher efficiency, and particulate matter tends to burn, but the amount of NO
x pollution tends to increase. NOx pollution can be reduced by recirculating a portion of an
engine's exhaust gas back to the engine cylinders, which reduces the oxygen quantity, causing

Diesel engine exhaust composition

Mass Volume
Species
percentage[141] percentage[178]

Nitrogen (N2) 75.2 % 72.1 %

Oxygen (O2) 15 % 0.7 %

Carbon dioxide (CO2) 7.1 % 12.3 %

Water (H2O) 2.6 % 13.8 %

Carbon monoxide (CO) 0.043 % 0.09 %

Nitrogen oxide (NOx) 0.034 % 0.13 %

Hydrocarbons (HC) 0.005 % 0.09 %

Aldehyde 0.001 % (n/A)

Particulate matter (Sulfate + solid

0.008 % 0.0008 %
substances)
a reduction of combustion temperature, and resulting in fewer NOx. To further reduce NO
x emissions, lean NOx traps (LNTs) and SCR-catalysts can be used. Lean NO
x traps adsorb the nitrogen oxide and "trap" it. Once the LNT is full, it has to be "regenerated"
using hydrocarbons. This is achieved by using a very rich air-fuel mixture, resulting in
incomplete combustion. An SCR-catalyst converts nitrogen oxide using urea, which is injected
into the exhaust stream, and catalytically converts the NOx into nitrogen (N2) and water
(H2O). Compared with an Otto engine, the Diesel engine produces approximately the same
amount of NOx, but some older Diesel engines may have an exhaust that contains up to 50 %
less NOx. However, Otto engines, unlike Diesel engines, can use a three-way-catalyst, that
converts most of the NOx.

Noise

Typical Diesel engine noise of a 1950s direct injected two-cylinder Diesel engine (MWM
AKD 112 Z, in idle)
The distinctive noise of a Diesel engine is variably called Diesel clatter, Diesel nailing, or
Diesel knock. Diesel clatter is caused largely by the way the fuel ignites; the sudden ignition
of the Diesel fuel when injected into the combustion chamber causes a pressure wave, resulting
in an audible ″knock″. Engine designers can reduce Diesel clatter through: indirect injection;
pilot or pre-injection; injection timing; injection rate; compression ratio; turbo boost; and
exhaust gas recirculation (EGR). Common rail Diesel injection systems permit multiple
injection events as an aid to noise reduction. Therefore, newer Diesel engines do not knock
anymore. Diesel fuels with a higher cetane rating are more likely to ignite and hence reduce
Diesel clatter.