Noise-canceling Spike between Pressure Rise Peaks of Pilot and Main Combustion in Diesel Engine

抄録

A previous study addressed combustion noise reduction by optimizing the interval between two peaks in the pressure rise rate (dP/dθ) of PCCI combustion with the split injection of fuel in diesel engines. Noise canceling occurs between two dP/dθ peaks, which reduces the overall combustion noise by lowering the maximum frequency component of the noise spectrum. The period of this frequency is twice the interval between the two dP/dθpeaks. We named this noise reduction technique ‘noise-canceling spike’ because it relies on interference between a spike in the pressure rise and the preceding peak in the pressure rise. On the other hand, the amplitude of the frequency component, the time period of which corresponds to the interval between the two dP/dθpeaks, increases as a result of the overlapping of these peaks. Therefore, the time interval between the dP/dθ peaks must be controlled precisely to enable the utilization of the noise-canceling spike. The noise-canceling spike is a universal phenomenon which occurs between the two dP/dθ peaks independently of the combustion (injection) strategy. If three dP/dθpeaks appear, the noise-canceling spike can occur between every pair of dP/dθpeaks. In this paper, we prove that the noise-canceling spike can occur between the dP/dθ peak of the pilot heat release and the multiple dP/dθ peaks of the main heat release in diesel combustion. The noise-canceling spike between the dP/dθ peak of the pilot combustion and the first dP/dθ peak of the main combustion becomes the dominating factor which reduces the overall combustion noise. The detailed mechanism of the noise-canceling spike is explained by 0-dimensional cycle simulations.