Abstract
For a considerable time now, the reduction of noise and vibration is one of the priorities of Renault for its Diesel engines. In this context, the optimization of Diesel combustion noise is related to a better understanding of the physical phenomena responsible of this noise. The conventional combustion process in Diesel engines includes two stages: the premixed combustion and the diffusion combustion. The aim of the present study is to explain the connections between the premixed combustion and the combustion noise.
In this paper, we present results of several experiments that can highlight the relationship between the noise and the combustion process in the premixing phase. Various tests were performed on a 1.5-liter DI (Direct Injection) Diesel engine. Variations of different parameters (fuel mass injected, common rail pressure, separation times between injections, injection advance) were carried out with single-injection strategy (1 main injection) and with multi-injection strategy (1 or 2 pilot injections + 1 main injection). The results of these tests show clearly the connection between the combustion noise and these parameters, particularly the amount of fuel burnt and the timing of pilot injections.
It has been shown that the combustion noise level was highly related to the mass of fuel burnt in the premixed combustion phase. In the case of one pilot injection, the optimal combustion noise is obtained with a small amount of pilot injection and small timing separation from the main. With two pilot injections, the combustion noise can be better than with single pilot injection, but can also be worse if the values of injection parameters are not appropriate. In this case, the optimal combustion noise can be obtained by adopting small amounts of two pilot injections, with small timing separation between them, but far for the main injection. These tests show also that the control of the injected flows, particularly the control of the small quantities for pilot injections, is essential for obtaining a good combustion noise.
KEYWORDS : Combustion noise, Diesel engine, Injection parameters, Premixed combustion, Fuel mass