Experimental study of combustion noise radiation during transient turbocharged diesel engine operation

Diesel engine noise radiation has drawn increased attention in recent years since it is associated with the passengers’ and pedestrians’ discomfort, a fact that has been acknowledged by the manufacturers and the legislation in many countries. In the current study, experimental tests were conducted on a truck, turbocharged diesel engine in order to investigate the mechanism of combustion noise emission under various transient schedules experienced during daily driving conditions, namely acceleration and load increase. To this aim, a fully instrumented test bed was set up in order to capture the development of key engine and turbocharger variables during the transient events. Analytical diagrams are provided to explain the behavior of combustion noise radiation in conjunction with cylinder pressure (spectrum), turbocharger and governor/fuel pump response. Turbocharger lag was found to be the main cause for the noise spikes during all test cases examined, with the engine injection timing calibration and the slow adjustment of cylinder wall temperature to the new fueling conditions playing a vital role. The analysis was extended with a quasi-steady approximation of transient combustion noise using steady-state maps, in order to better highlight the effect of dynamic engine operation on combustion noise emissions.

► Studying the effects of acceleration and load increase on the combustion noise radiation from a turbocharged diesel engine.
► Turbocharger lag was the most notable contributor for the behavior of combustion noise radiation.
► Turbocharged diesel engine behaves noisier at acceleration compared with the steady-state operation.
► Fuel limiter, governing and engine injection timing calibration play a decisive role on the emission of combustion noise.
► Transient noise radiation was smoothed the slower the acceleration and the smaller the demanded speed increase.