What is an internal combustion engine? Name the various types ?
An internal combustion engine is defined as an engine in which the mechanical power is
produced by combustion of fuel inside the engine cylinder. This is in contrast with steam
engine where combustion of fuel takes piace externally in a boiler to produce the steam
needed to drive the engine.
Internal combustion engines may be categorised into various types on different considerations.
◆ The main categories, based on the principle of working are 2-stroke and 4-stroke cycle
● 2 -Stroke Engines Working :-
In 2-stroke engines, after the ignition takes place, the piston moves downwards
(or outwards) and somewhat before reaching the end of stroke, exhaust valve or ports
open followed by the scavenge ports opening. Scavenging process i.e. evacuation of the
exhaust ga.ses and filling the cylinder with a fresh charge of air begins and continues for
some distance during the next stroke after which the air is compressed. Near the end of
the second stroke, fuel is injected, ignition takes place and the piston commences its
downward stroke again in the next cycle.
● 4 -Stroke Engines Working :-
In the case of 4-stroke engines, the process of alr intake, compression, ignition/expansion
and exhaust take place during separate strokes.
◆ From the point of ignition method, there are two types.
● Spark Ignition Type
● Compression Ignition Type
In the spark ignition type, a mixture of fuel (usually petrol) and air is supplied to the engine which is compressed and then
ignited by an electric spark. In the Compression ignition type, air is compressed and raised
to a high pressure and temperature and the fuel injected is ignited by the high alr temperature.
◆ From the point of scavenging method, a 2-stroke engine may be
● Loop Scavenge
(1) cross-scavenged where
exhaust and scavenge air ports are located in the liner approximately opposite to one
(2) return-loop scavenged where the exhaust ports are situated slightly above the
scavenge air ports on the same side of the liner
(3) uniflow scavenged in which the scavenge ports are situated near the botom of the liner and exhaust takes place through
a valve at the top of the cylinder.
◆ Internal combustion engines may also be categorized according to the running speeds.
●slow speed (75 to 140 rpm)
● medium speed (400 to 1200 rpm) and
● high speed (1800
rpm and above).
◆ Another classification is
● “in-line” and
● “V type”.
In most of the engines the cylinders are arranged vertically in one line.
In the V-type the cylinders are arrange in two rows inclined
to tho vertical in a V configuration.
In Conventional engines opening and closing of valves, fuel injection and air starting functions are controlled by cams.
In a new generation af engines-the so called “intelligent” engine.
-these functions are controlled electronically by computers that sense the crank angles
and regulate the timings as required.
◆ From the point of fuel injection method, an engine can be classed as one with
●jerk type fuel pumps or
● having a common rail fuel system.
Common rail system was prevalent in earlier
times and is now making a comeback again in some makes of intelligent engine.
Some of the internal combustion engine types are uncommon these days.
● 4-stroke double acting type in which both sides of the piston wero utilized for delivering
● 2-stroke opposed piston in which two pistons moved in opposite directions in the
● 4-stroke blast injection engine in which a metered quantity of low pressure fuel was injected by an air blast delivered under high pressure a through a cam operated valve.