Tuesday, 22 October 2013

Spark Ignition Engines

Internal combusiton engines are divided into spark ignition engines and com-
pression ignition engines. Almost all automobiles today use spark ignition
engines while trailers and some big trucks use compression ignition engines.
The main di erence between the two is the way in which the air to fuel mix-
ture is ignited, and the design of the chamber which leads to certain power
and e ciency characteristics.
Spark ignition engines use an air to fuel mixture that is compressed at high
pressures. At this high pressure the mixture has to be near stoichiometric
to be chemically inert and able to ignite. Stoichiometric means that there
is a one to one ratio between the air and fuel mixture. So the mixture in
order to ignite needs not to be either with too much fuel or too much air
but rather have an overall even amount. There are several components to
the spark ignition engine. Chamber design, mixture and the injection system
are some of the most important aspects of the spark ignition engine. The
importance of the chamber design will be discussed. The four basic designs
for combustion chambers are as follow:
--the distance travelled by the
ame front should be minimised
--the exhaust valve and spark plug should be close together
--there should be su cient turbulence 17
--the end gas should be in a cool part of the combustion chamber.




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