Research On Separation Method Of Radiated Noise Of Internal Combustion Engine And Quantitative Assessment Of Piston Slap Noise

The separation and identification technology of noise sources is the focus and hot spot in the field of internal combustion engine noise research.Piston slap noise and combustion noise are the main noise sources of internal combustion engine.They are almost occurred near top dead center,and they are aliased together in time domain and frequency domain.Thus it is very difficult to separate and identify them accurately and effectively.In the paper,the single-channel blind source separation method,piston slap noise calculation method and combustion noise acquisition method are studied to solve the separation identification and evaluation problem of piston slap noise and combustion noise.The main research contents are as follows.(1)A single-channel radiation noise test acquisition platform of internal combustion engine is designed and built in the marine engine laboratory.The lead-covering method of three-layer wrapping way is utilized to isolate the noise generated by other five cylinders.The sound absorbing board is built around the internal combustion engine to eliminate the reflection sound generated by other mechanical equipments and cabin bulkhead around the internal combustion engine.Through testing,the single cylinder radiated noise at different typical positions of internal combustion engine under different test conditions is measured to provide high-quality test data for the subsequent calculations.(2)In order to solve the problem of underdetermined blind source separation of single channel separation algorithm,the human ear hearing Gammatone filter bank model is studied.The Gammatone filter bank which is suitable for the separation and identification of internal combustion engine noise source is designed.Combined with independent component analysis algorithm,a Gammatone-RobustICA noise source separation algorithm based on human ear auditory model is proposed.The Gammatone-RobustICA algorithm is utilized to separate and identify the noise source at different working conditions and different typical positions of internal combustion engine.The research results show that the algorithm has good separation effect on piston slap noise,but the separation effect on combustion noise needs to be improved.(3)The data decomposition model is researched.When the VMD algorithm is used to decompose the non-stationary radiated noise signal of internal combustion engine,the under-decomposition and over-decomposition problem will be produced.To solve this problem,the mode number optimal variational mode decomposition(MNOVMD)algorithm is proposed.A single-channel MNOVMD-RobustICA noise source separation algorithm based on data decomposition model for noise source separation of internal combustion engine is proposed.The algorithm is used to separate the noise sources at six different typical positions of internal combustion engine under five different working conditions.It is found that the algorithm can separate the piston slap noise and combustion noise well.(4)The calculation method of piston slap noise based on dynamic model is studied.By analyzing axial reciprocating motion and lateral tilting motion of piston in cylinder liner,the dynamic equation of piston movement is obtained.Considering the influence of the lubricant film on the piston movement between piston skirt and cylinder liner,the piston dynamics equation coupled with Reynolds equation is further obtained.The vibration noise generated by piston hitting the inner wall of cylinder liner is calculated through this equation.Then the vibration noise of inner wall of cylinder liner is studied through the attenuation of body structure,and the independent piston slap noise is calculated.The piston slap noise extracted by single-channel blind separation algorithm is compared and evaluated with the calculated piston slap noise.(5)The generation mechanism of combustion noise of internal combustion engine is studied.The spectral filtering method is proposed to obtain the combustion noise.It mainly utilized to compare the performance of two single-channel blind source separation algorithms in separating and extracting combustion noise.After comparison and analysis,it is found that the purity of combustion noise extracted by MNOVMD-RobustICA algorithm is better than Gammatone-RobustICA algorithm,essentially because Gammatone filter bank is sparse in the high-frequency part of the bandwidth,and the decomposition accuracy is lower than MNOVMD algorithm.