Experimental Study On The Combustion Noise Of The Internal Combustion Engine

With the development of productivity，diesel engine trends to develop in thedirection of high-power and light-duty，but its vibration-noise problem becomes moreand more serious. The researchers at home and abroad have made a lot of explorationin source identification and separation technology of internal combustion enginenoise and have made a certain progress. The noise source of internal combustionengine is often complicated, if we can design and build independent noise simulationtest experiment to get the pure independence of combustion noise、mechanical noiseand air dynamic noise, and to obtain characteristics and the contribution ofindependent noise source, it can provide accurate information for sound qualitydesign of internal combustion to reduce the vibration and noise. The major method ofthe paper is experimental study, and combining with theoretical analysis, we obtainthe combustion noise by designing the combustion noise simulation test experimentand based on the transfer function method.The combustion noise simulation test experiment is designed and built on the4120SG direct injection diesel engine. The paper chooses pure oxygen and gasolineas accelerant and fuel, the gas mixture of which is used as a source of impulsepressure. The paper designs a suitable and easy ignition system used for igniting thesource of impulse pressure. A sparking plug in the shape of fuel injector which is thecore components of the ignition system is designed according to original assemblyinjector of the diesel engine cylinder4and the classic sparking plug.According to the trial objective and laboratory conditions, the paper selectssuccessfully test equipment and sets up the data acquisition system, and writes dataacquisition program based on the LabVIEW platform to realize the data acquisitiontask and data processing in late, then designs the particular test measurement plan toguarantee the successful acquisition in the impulse combustion pressure and itsradiant impulse sound pressure.The paper obtains the diesel engine combustion noise transfer function atdifferent sides using the impulse combustion pressure and its radiant impulse soundpressure at different sides collected from the combustion noise simulation test experiment, correlation coefficient value of the diesel engine combustion noise at theanti thrust side is relatively high, so the transfer function model at the side isrelatively accurate. The paper obtains the combustion noise of the direct injectiondiesel engine at the anti thrust side using the transfer function model at the anti thrustside and the cylinder pressure at the normal combustion condition. In the end, theauthor collects the block vibration signal at the anti thrust side of the4120SG directinjection diesel engine under the normal combustion condition, and intercepts thetime domain signal near TDC using the sampling interval method and calculates theresults of combustion noise from the vibration signal power spectrum.The results show that the combustion noise simulation test experiment can meet thetest and research purposes, and the pure combustion noise mainly concentrated in themiddle frequency of1.1kHz and1.4kHz nearly and around the high frequency of3.0kHz when the4120SG direct injection diesel engine is under normal combustioncondition without load.