Why are diesel driven vehicles noisy?
Diesel engines are inherently noisy because of the auto-ignition of the initially formed mixture of fuel-vapour and air, which causes rapid rate of pressure rise producing the characteristic noise. This abnormality is due to the inborn feature of a diesel engine, which uses a high compression ratio to obtain high fuel efficiency and a high compression-temperature for ignition of the fuel injected into the cylinder at high pressure. In a diesel engine, unlike a petrol engine, the air and fuel do not mix outside the engine. Air is compressed to a high compression ratio leading to high fuel efficiency, and also to a high compression temperature to initiate combustion. They just meet inside the combustion chamber for a brief period, while all the processes of mixture formation like fuel-jet break-up, evaporation and mixing should take place within a short time called ignition delay period. Combustion follows this after the initially formed fuel-air vapour auto-ignites with a noise, forming
