Experimental Study On Combustion Characteristics Of Internal Combustion Engine Based On Acouetic And Vibration Detection

Combustion characteristics analysis of internal combustion engine is a systematic and complex interdisciplinary project.In order to analyze the combustion characteristics of the internal combustion engine,the traditional experimental method is usually based on the collected in-cylinder pressure signal with the use of an engine combustion analysis software to analyze the cylinder pressure signal,obtaining the curves of combustion characteristics and important value under various conditions.However,in order to collect the cylinder pressure signal,it is necessary to drill the cylinder head to install the pressure sensor,resulting in invasive destruction,and the pressure sensor need to work in high temperature environment,so the sensor requirements are much higher.The author solves the above problems by replacing the cylinder pressure signal with the combustion noise signal extracted from the total noise of the internal combustion engine to achieve long-range non-intrusive monitoring.In this paper,an experimental study was carried out to investigate the combustion characteristics of a compression ignition diesel engine fuelled with biodiesel blends.The research results are listed below:(1)The variation of cylinder pressure,the pressure rising rate,the heat release rate and the ignition time were examined through the comparative analysis based on the test data,which was collected using pure diesel oil,bio diesel mixed half(B50)and pure biodiesel(B100)three kinds of fuel.It provided a theoretical basis for the analysis of combustion noise characteristics and provides data support for the development of new alternative fuels.A coherent power spectrum analysis method was used to investigate the noise and cylinder head vibration signals that related to the combustion process.The result showed that noise signals closely related to the combustion process was combustion noise at frequency band of 2 ~ 3KHz.(2)Time synchronous average(TSA)was used for pretreatment to enhance the signal-to-noise ratio of acoustic signal by suppressing the components which were asynchronous.The processed acoustic signals were decomposed into a series of intrinsic mode functions(IMF)using the method of empirical mode decomposition(EMD)in time domain.Then wavelet analysis which has good time-frequency localization feature was applied on useful IMFs containing the information of diesel engine combustion.The root mean square(RMS)value of wavelet analysis was calculated to achieve linear state monitoring.(3)The Wigner-Ville distribution(WVD)which has a good time-frequency energy distribution was windowed with the function Choi-Williams for suppressing the generation of cross terms.It was conformed a good effect by an analog signal simulation.A band-pass filter based on fractional Fourier transform was developed to extract the main component of the combustion noise.Time-frequency analysis of the extracted combustion noise was done by using WVD method windowed function Choi-Williams.Finally,the sound pressure level of the extracted combustion noise part was calculated to achieve the purpose of combustion characteristic analysis and fuel quality evaluation.