Simulation On Fuel-air Equivalence Ratio And Pilot Injection Strategy Of Low Pressure Dual Fuel Engine

In order to effectively reduce the pollutants discharged in the marine transportation,the International Maritime Organization（IMO）has promulgated the “MARPOL”,whose strict emission regulations put forward new requirements for the marine engine emission reduction technology.Taking natural gas as alternative fuel is an important technical path to meet the increasingly strict emission regulations.In this paper,a low pressure injection dual fuel engine is taken as the research object,by means of one/three-dimensional numerical simulation,the effects of fuel-air equivalence ratio and pilot oil injection parameters on the performance and emissions of the whole engine are studied,the appropriate fuel-air equivalence ratio and pilot injection strategy are established.First of all,a one-dimensional simulation model of the engine is established by GT-Power software.The model is run under multiple operating conditions,and the calculation results are verified with the measured results.This model is used to simulate and calculate the fuel-air equivalence ratio and pilot oil injection timing,the influence of these two parameters on engine performance and emissions is studied,and the interaction between the two parameters is analyzed.It is preliminarily determined that the fuel-air equivalence ratio should be controlled at about 0.4 as much as possible,and the value range of pilot oil injection time is around-6°CA and-4°CA,which will lay a foundation for the following three-dimensional modeling and simulation calculation.Secondly,UG and CONVERGE software are used to build the three-dimensional simulation model of the engine,and the model is run under rated conditions,and the cylinder pressure curve and NOx emission are verified.Based on this model,the scavenging process,natural gas premixing process,combustion process and NOx derivative process of the engine are analyzed,mainly including temperature change,flow field change,concentration change of components,etc.The working process of the engine is further mastered,which lays a foundation for the subsequent study of pilot injection strategy.Finally,using the three-dimensional simulation model verified above,the main parameters of pilot oil injection strategy: pilot oil injection timing,injection volume,injection pressure are simulated and calculated,and the influence of these three parameters on the cylinder pressure and temperature,NOx emission,HC emission,temperature field distribution,natural gas combustion process and NOx derivative process are analyzed in detail.In addition,the influence amplitude of these three parameters on the above-mentioned response quantity is compared and analyzed,and the rationality of establishing injection timing,injection quantity and injection pressure successively is verified,and the final pilot oil injection strategy is determined as follows: pilot oil injection timing is-5°CA,oil-gas mass ratio is 1% and pilot oil injection pressure is 1050 bar.Under the pilot oil injection strategy,NOx emission is only2.88g/k Wh,HC emission is only 1.84g/k Wh,and the maximum pressure rise rate is within0.6MPa/°CA.Combined with the independent research and development process of low-speed dual fuel engine in China,based on one/three-dimensional numerical simulation,this paper carries out preliminary research on fuel air equivalence ratio and pilot oil injection strategy,which provides a reference for the development and design of similar models in the future.