Effects Of Combustion System Parameters On Combustion Characteristics Of A Dual Fuel Engine

The serious problem of energy and environmental pollution has promoted the development of efficient and clean combustion technology for marine engines.Dual-fuel engine has received extensive attention owing to such features as high combustion efficiency,low emission,flexibility and redundancy of operating mode.The combustioin of dual-fuel engine is affected by combustion chamber structure,gas supply system,air and fuel supply system,which leads to a more complicated combustion organization.Therefore,it is important to further study the influence of matching of combustion system parameters on the combustion characteristics of dual-fuel engine.The marine dual-fuel engine was used in this study.The influence of the structural parameters of the combustion chamber(bowl radius,depth and inclination angle)and the fuel injection timing on the combustion characteristics of the dual fuel engine were studied using the CFD simulation analysis method.This study is to provide theoretical guidance for optimization of the combustion process of dual fuel engine.Based on the sensitivity analysis of the combustion chamber structural parameters,three different combustion chamber structures were designed while maintaining the original compression ratio.The influence of different combustion chamber structures on the combustion characteristics for dual fuel engine was studied using CFD software.The results show that reducing the radius and the inclination angle of the bowl can increase the airflow velocity in the combustion chamber,which is beneficial to promote the mixing of natural gas and air.By adjusting the ratio of the radius and the depth of the bowl and changing the inclination angle,the eddy current can be reasonably utilized in the cylinder.The formation of a suitable mixture concentration is beneficial to improve the combustion characteristics of the dual-fuel engine.The turbulent energy significantly attenuate owing to the presence of the bulge,but reducing the inclination angle of the bulge appropriately can enhance the turbulent kinetic energy and improve the flame propagation speed,which is beneficial to accelerated combustion process.In order to comprehensively consider the coupling effect of combustion chamber structure and fuel injection parameters on the combustion process,the effects of gas injection timing and fuel injection timing under different combustion chamber structure on the combustion process were analyzed based on the study of the influence of combustion chamber structure.The results show that adjustment of the gas injection timing can improve the gas flow velocity and intensify the turbulent energy in the combustion chamber.Under the function of the airflow,a proper mixture distribution can be formed and improve the combustion process.Advancing of fuel injection timing,the pressure and the heat release rate of the cylinder are significantly improved,the combustion duration is shortened,and the CA50 moves closer to the top dead center.According to the comprehensive analysis of the results,for the 1# combustion chamber,when the gas injection timing is 370°CA and the fuel injection timing is 703°CA,the combustion speed of gas-air-fuel mixture is accelerated,and the peak of the heat release rate and the peak pressure of the cylinder is improved,and better combustion characteristics can be obtained.Compared with other schemes,the combustion temperature is lower,which is beneficial to the nitrogen oxide emission,and the engine performance is improved.