INTERNAL COMBUSTION ENGINE (RECIPROCATING)

The reciprocating internal combustion engine also known as the piston engine is a heat engine that converts chemical energy into mechanical energy, using the reciprocating motion of one or more pistons to convert the action of high temperature and high pressure gases into a rotating motion.

The main components of a reciprocating internal combustion engine are; pistons, crankshaft, camshaft, valves, fuel system and the ignition system.

The cylinders are the chambers where the combustion of the air- fuel mixture takes place to produce power to push up the piston.

The piston in its motion up and down the cylinder, driven by the explosive force of the fuel mixture expanding moves up and subsequently downwards as the exhaust gases are expelled from the cylinder.

The crankshaft converts the up and down movement or motion of the pistons into rotary motion, which is transferred to drive the load connected to the output shaft.

The camshaft operates the inlet and outlet valves that allow air and fuel into the cylinder and exhaust gases out of the cylinder.

The fuel system delivers fuel into the cylinders from the fuel tank, fuel pump, fuel filters and fuel injectors.

The ignition system generates the spark or heat necessary to ignite the fuel-air mixture inside the cylinder.

Reciprocating internal combustion engines are classified according to these basic criteria; the type of fuel, ignition system, the number and arrangement of cylinders, the engine capacity and other minor classifications.

The type of fuel used in reciprocating internal combustion engines are mainly gasoline or petrol and diesel, though other fuels like compressed natural gas, liquefied petroleum gas, ethanol, biodiesel and other mixed fuel can be used.

There are two types of ignition system used in reciprocating internal combustion engines; they are the spark ignition and compression ignition. Spark ignition engines use a spark from a spark plug to ignite the compressed fuel-air mixture. While compression ignition engines compresses air to a high pressure, heating the air to the ignition temperature of the fuel, before mixing or injecting it into the fuel to ignite it.

The higher compression ratio used for compression ignition engines results in a higher efficiency than is possible for spark ignition engines.

Reciprocating internal combustion engines operate in four strokes or two stroke cycle. Most reciprocating internal combustion engines, especially those used for automotive applications operate a four stroke cycle. While a two stroke cycle engine operates in two strokes, the power stroke and the exhaust stroke. Two stroke engines produce more power per unit of weight and are commonly used in applications like aircraft and marine engine where weight consideration is a critical factor in design and operation.

Reciprocating internal combustion engines are also classified according to the number and the arrangement of the cylinders. The most common number of cylinders is; one, two, four, six, eight, ten, twelve or more. The reason for this is to ensure a smoother ride characteristics and vibration reduction in the power delivery to the entire vehicle of power plant.

Reciprocating internal combustion engines are also classified according to their engine capacity; they are classified as smaller engines if their capacity is less than 1.5 liters, as medium if their capacity ranges between 1.5 and 3.5 liters and large if their capacity is between 3.5 and 6.5 liters and very large if their capacity is greater than 6.5 liters.

Other minor classifications that exist are the method of cooling or whether is water cooled or air-cooled and the fuel supply or mixture preparation or whether it uses a carburation or an injector system.

The relative advantages of reciprocating internal combustion engine of other power plants are their high power to weight ratio, low initial cost, wide range of applications and a well-established support infrastructure.

The disadvantages are their low efficiency usually of between 20% and 39%, emission of a wide range of pollutants, noise due to vibration and their dependence on non-renewable energy resource.

The applications of reciprocating internal combustion engines are diverse and they find widespread use in the automotive, aircraft, marine and as power plants in industry.

The future of reciprocating internal combustion engines look bleak considering the increased adoption of electric vehicles and electric motors as prime movers in industry because of their more excellent conversion efficiency and their green operational nature or environmental friendliness and their low maintenance cost .

Despite these drawbacks, it is noteworthy to point out that research and development efforts are on the way to improve their efficiency, reduce emission and noise pollution.

 

SOURCES:

• Internal combustion engines fundamentals by John B. Heywood.
• Engineers handbook of internal combustion engines by Ganesan.
• The internal combustion engine in theory and practice by Charles Fayette Taylor.
• Internal combustion engine design by Alan J. Glassman.
• Engines builders handbook by David Vizard.