Internal Combustion Engine (IC Engine)

The internal combustion (IC) engine are employed in automobes. In order to run these engine, the air- fuel mixture burns in the engine cylinder to develop power. Following are the two type of IC engines which are commonly used in automobiles:-

1. Petrol engine (Spark ignition engines):― In petrol engines,the air and fuel (petrol) mixture is drawn during suction stroke. The mixture is compressed to approximately 20 to 30 bar (compression ratio 6 to 10) in the compression stroke, thus raising the temperature in range 400 to 500℃ . The temperature reached after compression is below the auto-ignition threshold of the air fuel mixture and thus it is ignited with the help of a spark plug before the piston reaches the top dead center (TDC).                            The petrol engine works on Otto cycle (also known as constant volume cycle). In Otto cycle , combustion takes place at constant volume, as whole of the fuel is burned instantaneously as an explosion.
2. Diesel engine (Compression ignition engines):― In diesel engines, the air is drawn during the suction stroke, which is compressed to approximately 30 to 45 bar (compression ratio 14 to 25), thus raising the air temperature in the range 700 to 900℃ . Into this glowing hot air , the duel (diesel) is injected through a nozzle and finally dispersed . It evaporates, mixes with air and ignites spontaneously. During combustion , the pressure increases in the range of 55 to 75bar. The burned gases, under full load, are at temperature of about 600℃ but in case of petrol engines it is 900℃ . Thus , it may be noted that diesel engines utilizes the heat of the fuel to a better degree and for this reason it's fuel consumption is lower.                                                        The diesel engine works on diesel cycle( also known as constant pressure cycle). In diesel cycle, the combination takes place at constant pressure because burning takes place gradually, without an explosion as the fuel enters.