Experimental investigation on the relationship between in-cylinder pressure rise rate and combustion noise of the diesel engine

As a crucial emission element of mechanical structure, noise significantly impacts engine performance through its contribution to the NVH index. This study focuses on investigating combustion noise in diesel engines, and a dedicated noise test bench was constructed for this purpose, enabling the measurement of both in-cylinder pressure and generated noise. Through analysis of the time and frequency domains of the test signals, the primary sources of engine noise are identified, elucidating the relationship between in-cylinder pressure and combustion noise. The research reveals the nonlinear nature of diesel engine combustion noise, particularly noting local extreme values occurring within specific engine speed ranges, and it suggests that engine noise may predominantly stem from cavity resonance. Then, a correlation is established between the in-cylinder pressure rise rate and combustion noise level, indicating that higher pressure rise rates lead to more turbulent combustion processes within the chamber, and this turbulence reinforces cavity resonance strength, resulting in louder combustion noise. Finally, strategies for noise reduction are proposed, indicating that lowering the in-cylinder pressure rise rate can shift combustion noise to lower frequency bands and diminish resonance strength, thereby mitigating noise levels.