Engines are the major components of any automobile. A user of an automobile wants
to get maximum power output from the engine, at the same time, not sacrificing
fuel efficiency. The
design of an engine is very important. One of the most important parts of engine
design is the design of the combustion chamber. Different types of combustion
chamber heads are being used at present.
One type of chamber head is the hemispherical head. The hemispherical head design
enables the user to extract more power from the engine. The engines using hemispherical
heads are known as HEMI engines.Modern
HEMI engines are using various developments that have come up in the recent past.
This has enabled these engines to provide the user with additional advantages
apart from serving its major purpose, ie, supplying more power.
is the basic component of any automobile. Combustion engines may be divided into
two general classes - internal combustion engines and external combustion engines.In
the external combustion engines, a working fluid is utilized to transfer some
of the heat of combustion to that portion of the engine wherein this heat is transformed
into mechanical energy.
The internal combustion engine inducts air from the atmosphere and the combustion
of fuel and air occurs in or near that portion of the engine, which converts heat
to mechanical energy. Internal
combustion engines may be further classified into reciprocating engines and non-reciprocating
engines. Internal combustion engines may also be divided as spark ignition engines
and compression ignition engines.
Spark ignition engines may work in a two-stroke cycle or a four-stroke cycle.
The four strokes involved are
1) Intake stroke
2) Compression stroke
4) Exhaust stroke
two strokes of a four-stroke engine will be coupled in a two-stroke engine.
HEMI engine is a four stroke, spark ignition, reciprocating type, internal combustion
of the combustion chamber for a spark ignition engine has an important influence
on the engine performance and its knocking characteristics. The design involves
the shape of the combustion chamber, the location of the spark plug, and the location
of the inlet and exhaust valves. The important requirements of a spark ignition
engine combustion chamber are to provide higher power output with minimum octane
requirement, high thermal efficiency and smooth engine operation.
engine was first developed in 1951 by the Chrysler Corporation. The advantage
of HEMI engine over other engines of the time was that it produced more power.
The reason for this was the efficiency of the combustion chamber.
Most cars prior to the 1950's used what was known as a flathead and many lawn-mower
engines still use the flathead design today because it is less expensive to manufacture.
In a flathead engine, the valves are in the block, rather then in the head and
they open in a chamber beside the piston.
The head in a flathead engine (fig. 2.1) is extremely simple- it is a solid metal
casting with a hole drilled in to accept the spark plug. The camshaft in the block
pushes directly on the valve stems to open the valves, eliminating the need for
push rods and rocker arms. Everything is simpler in the flathead engine. The problem
with a flathead engine is its thermal efficiency.
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