Analysis Of Combustion Characteristics Of Diesel Alternative Fuels Based On Vibration Signals

Diesel engines are widely used in many fields such as industry and transportation.However,they consume petroleum resources and generate exhaust gas pollution.Therefore,the use of clean alternative fuels provides a new way to solve this problem.The operating conditions of diesel engines are complex,the working environment is harsh,and the possibility of failure is high,so it is particularly important to monitor the working status of diesel engines.At present,the non-intrusive monitoring of the engine’s combustion process based on vibration signals is a common method for mechanical equipment condition monitoring.The analysis of vibration signals is of great significance for the realization of closed-loop control,online monitoring and fault diagnosis of the combustion process of internal combustion engines.In this paper,different proportions of biodiesel and 0# diesel,F-T diesel and biodiesel,methanol and 0# diesel are mixed into biodiesel blended fuel,F-T diesel blended fuel and methanol blended fuel,respectively,and burned in a diesel engine.As the blending ratio changes,the physical and chemical characteristics of the blended fuels will also alter,so the combustion characteristics and vibration characteristics of the engine show different trends.Continuous wavelet transform was used to analyze the vibration signal in time and frequency,and the influence of the blending ratio on the combustion and vibration characteristics of the diesel engine was studied.In the biodiesel blended fuels,biodiesel has a high cetane number and contains oxygen in the molecule.As the proportion of biodiesel in the blended fuel increases,the start of combustion advances,the peak pressure in the cylinder increases,and the peak phase gradually advances.The vibration energy near the combustion TDC is greater than the energy at other crankshaft angle positions.With the change of the biodiesel proportion in the blended fuels,the change trend of the vibration peak for each fuel in different frequency bands is different.In general,the vibration energy of the blended fuels are much than that of 0# diesel.The cetane number of F-T diesel in the F-T diesel blended fuels is higher.As the proportion of F-T diesel in the blended fuel increases,the combustion start point advances,the peak of cylinder pressure rises,and the peak phase advances.Under low load conditions,the peak pressure increase rate of F-T diesel is larger,and under high load conditions,the peak pressure increase rate of biodiesel is larger,which is caused by the change of the thermal conditions in the combustion chamber.The peak value of vibration for each blended fuel in different frequency bands shows different changes.The cetane number and low calorific value of methanol in the methanol blended fuels are relatively low.At low speed conditions,a small proportion of methanol blending will help to increase the peak pressure of the cylinder.Under high speed and high load conditions,much fuel is needed in the cylinder to replenish,at this time the peak pressure of the cylinder is decreased.In different frequency bands,the vibration peak of 0# diesel and a small proportion of methanol blended fuels is higher.By analyzing the action mechanism of the main excitation source of the diesel engine,it can be seen that the combustion shock and the side impact of the piston are the main excitation sources that cause the vibration response of the diesel engine body.The relationship between combustion shock and vibration has been studied.The side impact event of the piston mainly corresponds to the vibration response of the low frequency band.The vibration response of the middle frequency band is mainly generated by the combustion shock excitation.The response event of high frequency band is mechanical structure vibration caused by combustion excitation.At the same time,the relationship between combustion shock and piston side impact to vibration response was established.It is considered that analysis of the combustion characteristics of diesel engines based on vibration signals can be carried out through two ways: combustion event and vibration response,side impact event and vibration response.