Noise of Diesel Engines Under Transient Conditions

Diesel engines accelerating under full load conditions radiate more noise from their surfaces than when they are run at steady speed with the same fuelling. This is particularly marked in urban driving conditions as engines are accelerated after running for long periods at idling or at part load, when the inlet manifold and piston temperatures are lower than they are at steady speed full load conditions. The work reported in this paper shows that the increase in noise originating from the combustion process is due to the lower temperature of the air charge. It is also shown how mechanical noise from piston slap increases under acceleration conditions.