| The ion current produced in combustion process contains rich combustion information.The signal characteristics of ion current is closely related to operating condition of the fuel combustion.The ion current method has great economic and technical advantages compared to traditional monitoring technology in monitoring engine operation parameters.The ion current signals produced in the combustion ionization process of the in-cylinder mixture can be used to simultaneously on-line monitor several combustion operating parameters of internal combustion engine,and thus the internal combustion engine operating conditions can be adjusted in time according to effective feedback information of ion current,and thus the precise control of ignition and combustion process of internal combustion engine can be realized.As a new on-line monitoring method,Ion current method has become a research focus in the field of combustion measuring and control of internal combustion engine.The combination of internal combustion engine and renewable energy will have a far-reaching influence on the existing energy system.The clean renewable gas fuel,represented by hydrogen-mixed natural gas fuel,has gradually become research hotspot of engine alternative fuel in recent years.In order to realize effective on-line monitor of the gas fuel combustion process using the ion current method,and to improve the combustion quality of gas fuel,in the hope of reaching good power performance,higher economy and lower emission,it is necessary to further study the laminar combustion characteristics and the ion current characteristics of the hydrogen and natural gas mixed fuel.According to the flame propagation schlieren pictures,the correlation between the combustion characteristics and ion current characteristics need to be further understood so as to further provide basic experimental data and theoretical support for design of gas engines and utilizing the ion current signals to realize the precise control of combustion process.This paper takes the laminar flame combustion characteristics,the ion current characteristics in the combustion process,and the correlation between the combustion characteristics and the ion current characteristics of natural gas/hydrogen/CO2 gas mixture as the research key points under different initial conditions.The experimental and numerical simulation study of the laminar premixed flame combustion characteristics and ion current characteristics have been carried out.The research work illustrates the effect of initial parameters of gas mixture on the laminar flame combustion characteristics and the ion current characteristics.The flame ionization mechanism of flame development and evolution process are revealed,and the intrinsic relationship between the flame propagation process and the ion current waveform is obtained.The new numerical calculation model of ion current in the combustion process is established.The correlation between the ion current characteristics and combustion mass,combustion pressure,and combustion heat release rate are obtained.The laminar premixed flame combustion characteristics of natural gas/hydrogen/CO2 mixed gas have been experimentally studied in constant volume combustion bomb.The experimental platform of the measurement system of ion current was established,and the data acquisition and processing program of ion current was developed and designed.The dynamic data collecting of laminar flame combustion and ion current were realized by using high speed schlieren photographs systems.The variation of flame radius,the laminar flame burning velocity and the flame stretch rate versus combustion duration time were analyzed under different initial condition.The influence of different initial parameters on the flame combustion characteristics were obtained by analyzing the flame spread pictures in combustion process.The ion current formation mechanism of laminar flame in gas mixture combustion process was studied and the numerical calculation model of ion current was established.Based on the flame ionization mechanism of different development periods of flame,the ion current calculation model of the chemical ionization reaction period and the thermal ionization reaction period was established,respectively.The influence of the flame radius,chemical reaction dynamics,ionization equilibrium,thermodynamics,ionization energy,electrode geometry and electric field on ion current are analyzed,and the influence rule of ionization energy,ionization rate,temperature and equivalent ratio on the generating concentration of charged ion were revealed.The quasi-dimensional two-zone combustion model was applied to solve the numerical solution of ion current,and the correctness of the ion current model is validated.The ion current characteristics of natural gas/hydrogen/CO2 mixed gas laminar flame in combustion process have been experimentally studied in constant volume combustion bomb.The influence of different initial parameters on the ion current characteristics are analyzed,and the intrinsic relationship between the different development periods of flame and the ignition period,the chemical ionization period,the thermal ionization period of ion current waveform were revealed.The influence of electric field voltage,electrode diameter,electrode gap and effective measurement area of electrodes on the characteristics of ion current waveform were analyzed,and the evolution rule of ion current waveform characteristics with combustion duration time under different initial conditions were obtained.The correlation between the combustion mass,combustion pressure,combustion heat release rate and the ion current characteristics of natural gas/hydrogen/CO2 mixed gas are studied in constant volume combustion bomb.Based on the correlation between the characteristics of ion current signal and combustion mass,the new method for calculating the burned mass fraction was established using the waveform parameters of ion current and Weber function.This method can obtain the shape factor and efficiencyfactor of the burned mass fraction based on the specific combustion process.The calculation error is reduced and the calculation accuracy is improved.Based on the correlation between the ion current signal and combustion pressure in the combustion process,the corresponding relationship between the ion current chemical ionization peak time,the thermal ionization current first derivative peak time of ion current and the maximum value time of pressure rise rate and pressure peak time were revealed,and thus a new method for the feedback adjustment of spark advance angle based on the ion current signal is provided.Based on the correlation between ion current signal and the heat release rate,the intrinsic relationship between the flame ionization reaction mechanism,the concentration of charged ion and the heat release rate were revealed.The correlation between the heat release rate waveform and the ion current waveform was obtained,and the conclusion will provide the theoretical basis and a new technological path for analyzing and acquiring the combustion heat release rate based on ion current signals. |
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