Combustibility
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Transcript of Combustibility
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SHEIKH SHAHIR MUHAMMAD AFIFUL ISLAM TITLE:
KEM120702 Requirement of Fuels Quality for CI(diesel) Engine
INTRODUCTION
A compression-ignition engine or commonly known as a diesel engine is an internal
combustion engine in which used a higher compression of the fuel to ignite the fuel
rather than using spark plug (spark ignition). Air is compressed adiabatically with a
compression ratio typically between 15 and 20. his compression raises the
temperature to the ignition temperature of the fuel mi!ture which is formed by in"ecting
fuel once the air is compressed.
FUEL CHARACTERIZATION
he fuel used in a compression ignition (#$) engine is diesel% which is a type of
hydrocarbon. &or hydrocarbons to 'ualify as a fuel for the engine% they should possess
certain 'ualities to be the ideal fuel for these engines.
i. nocking characteristics heoretically as soon as diesel fuel is in"ected into the
cylinder% it starts burning. *ut in practical situations this ne+er happens as there is
always a time lag between the in"ection of the fuel and burning of the fuel. As the
duration of ignition lag increases% the amounts of fuel get accumulated in the cylinder
head will also increased. ,hen the fuel is finally burnt% e!cessi+ely large amounts of
energy is released% which produces e!tremely high pressure inside the engine. his
causes the knocking sound inside the engine. hus the engines should ha+e a short
ignition lag so that the energy is produced uniformly inside the engine and there is
no abnormal sound. he knocking capacity of the fuel is measured in terms of
cetane rating of the fuel. $t should ha+e a cetane number high enough to a+oidknocking of engine.
ii. A$ gra+ity enerally% there is a /-5 decrease in the thermal energy content of
fuel for e+ery 10 degree increase in A$ gra+ity. his decrease in energy content will
result in roughly the same percentage decrease in engine power. se of fuels with
higher A$ gra+ity will also result in higher fuel consumption. $t is recommendation to
include a ma!imum A$ gra+ity is based on our understanding of customer needs to
maintain engine power% while minimiing fuel consumption.
iii. 3olatility of the fuel horough mi!ing of the fuel and air when fuel is in"ected in the
cylinder head ensures uniform burning of the fuel. he fuel should be +olatile in
nature within the operating temperature range of the cylinder head so that it gets
con+erted into a gaseous state and mi!es thoroughly with compressed air.
i+. 4tarting characteristics of the fuel he smooth starting of the +ehicle depends
greatly on the fuel used for the +ehicle. &or easy starting of the +ehicle it is important
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that the fuel has good +olatility so that it mi!es with the air uniformly and it readily
forms intothe combustible mi!ture. $n a particular diesel engine% higher cetane fuels will ha+e
shorter ignition delay periods than lower cetane fuels which in turn will lead to faster
starting of the +ehicle.
+. 4moke produced by the fuel and its odor iesel e!haust is a comple! mi!ture of
thousands of gases and soot that contains more than 60 to!ic air contaminants.
hese include suspected cancer-causing substances% such as benene% arsenic and
formaldehyde. $t also contains other harmful pollutants% including nitrogen o!ides. As
we breathe% the to!ic gases and small particles of diesel e!haust are drawn into the
lungs and are small enough to penetrate deep into the lungs% where they contribute
to a range of health problems. 4o the e!haust gases produced from the fuel should
not ha+e too much smoke and odor.
+i. 3iscosity of the fuel 3iscosity affects in"ector lubrication and fuel atomiation. &uels
with low +iscosity may not pro+ide sufficient lubrication for the precision fit of fuel
in"ection pumps or in"ector plungers resulting in leakage or increased wear. &uels
which do not meet +iscosity re'uirements can lead to performance complaints. &uel
atomiation is also affected by fuel +iscosity. iesel fuels with high +iscosity tend to
form larger droplets on in"ection which can cause poor combustion and increased
e!haust smoke and emissions. 4o the fuel should ha+e enough +iscosity so that it
can easily flow through the fuel system and the strainer at the lowest working
temperatures.
+ii. etergency All diesel fuels which do not contain detergents ha+e a tendency to form
carbon deposits on fuel in"ectors. $t has generally been found that low sulfur fuelsand thermally unstable fuels ha+e a greater tendency to form these deposits.
etergent additi+es will pre+ent carbon deposits% which interfere with fueling and fuel
spray patterns% from forming. irty in"ectors will in+ariability gi+e rise to higher smoke
le+els in all e'uipment and in some e'uipment can limit power by restricting fuel
flow.
+iii. 7ubricity 7ubricity describes the ability of a fluid to minimie friction and damage
between surfaces in relati+e motion under loaded conditions. iesel fuel in"ection
e'uipment relies on the lubricating properties of the fuel. 7ack of fuel lubricity can
shortened the life of engine components such as fuel in"ection pumps and unitin"ectors.
CONCLUSION
*ecause of the uni'ue combination of power% performance% energy efficiency% reliability
and low-emissions% diesel engines are the undisputed workhorse of the global economy%
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SHEIKH SHAHIR MUHAMMAD AFIFUL ISLAM TITLE:
KEM120702 Requirement of Fuels Quality for CI(diesel) Engine
powering almost all super-sectors including agriculture% construction% transportation%
mining and many more.