Research On The Effect Of Control Strategy On The Noise Of A Four-cylinder Turbocharged Intercooled Diesel Engine For Light-duty Vehicle

Diesel engines are widely used in automobiles due to their performance,drive ability and lower fuel consumption.However,with the increasing number of vehicles,especially in densely populated urban areas,the noise generated by vehicles has become the main source of noise in cities.The characteristic excitation frequency range of diesel engine noise is in the highly sensitive human perception range.It is difficult to optimize the engine noise due to the complex noise sources and operating conditions.Thus,engine manufacturers are focused on reducing the overall noise in diesel engines to comply with future legislations,and improving the sound quality perceived by the customer subjectively because of its influence on the purchasing decision.The engine noise was analyzed and optimized by control parameters and components of a four-cylinder turbocharged intercooled diesel engine for light-duty vehicle.Firstly,the law between in-cylinder pressure and near-field noise signal in the time and frequency domains was analyzed by structural attenuation,the coherence function and highfrequency pressure oscillation.The influence of in-cylinder pressure on engine noise was analyzed at different speeds and loads.Results show that the in-cylinder pressure has a strong coherence with the near-field noise signal in the frequency of 3000-5600 Hz.Meanwhile,the structure of diesel engine has the least noise attenuation in this frequency band.Therefore,it is easy to radiate higher sound pressure level in this frequency band.The pressure oscillations produced by combustion have a great influence on engine noise.It is easy to produce high frequency pressure oscillation,especially under the condition of low load and high speed,.Secondly,the effects of fuel injection parameters and EGR(Exhaust Gas Recirculation)valve opening on engine noise under various operating conditions were studied by spectrum analysis.Results show that pilot injection deteriorates engine noise at idle speed;at high load condition,small quantity of pilot injection can decrease the amount of fuel air mixture in the ignition delay,so that the sound pressure level generated by the main combustion is reduced.Excessive pilot injection quantity simultaneously deteriorates noise generated by pilot combustion.Moreover,the oscillating pressure wave of the pilot combustion immediately overlaps and influences the pressure wave generated by the pre-mixed combustion of the main combustion,leading to the increase of the engine noise.Proper delay of main injection can effectively reduce the engine noise.Advance of pilot injection slightly increases the sound pressure level in the low frequency band.Proper increase of EGR valve opening can reduce the engine noise at idle speed.Finally,the noisy components of diesel engine were optimized.The noise source of diesel engine is complex and interferes with each other,so it is necessary to identify the noisy components from the complex noise source.Then,the near-field noise microphones were arranged to carry out the comparative test on different components and analyzed their influence on engine noise.In addition,the near-field noise signal of diesel engine under transient condition was analyzed.Results show that the noise contribution rate of generator and air filter are higher under low load and high load respectively.The generator with larger stator stiffness and air filter with smaller porosity can significantly reduce engine noise.The second,fourth and eighth order noise of diesel engine are the most obvious.The fourth-order noise produced by piston impact needs to be optimized.