Combustion Noise Quality Improvement in a Common rail Diesel Engine at Low Idle using Taguchi DOE

Noise quality at idle condition is an important factor which influences customer comfort. Modern diesel engines with stringent emission norms together with fuel economy requirements pose challenges to noise control. Common rail engine technology has advantage of precise fuel delivery and combustion control which needs optimization to achieve the conflicting requirements of noise, emission and fuel efficiency. Engine noise at low idle condition is dominated by combustion noise which depends on rate of pressure rise inside the cylinder during combustion. The important parameters which influence cylinder pressure rise are fuel injection timing, pilot injection quantity and its separation, rail pressure and EGR valve position. The study on effect of these parameters at varying levels demand large no of experiments. Taguchi design of experiments is a statistical technique which can be used to optimize these parameters by significantly reducing no of experiments needed to achieve the desired results. These five CR parameters are varied at five different levels using an L25 Taguchi orthogonal array and noise measurements are conducted. The results of experiment have indicated that rail pressure has the highest effect on noise quality with 5dBA difference between the lowest and highest level of rail pressure. The second most significant parameter is pilot quantity with 3 dBA improvement by introducing pilot injection and the quantity of pilot injection needs to be kept minimum. Main injection timing has the potential of 1dBA and EGR valve position and pilot separation has very less influence. Engine calibration is optimized based on above inputs to meet the emission requirements and with the optimized calibration noise is improved by 5dBA at low idle