Simulation Of Optimization Of Combustion Chamber For Diesel/Natural Gas Dual-Fuel Engine

In order to alleviate the atmospheric pollution caused by marine diesel engine,search for alternative energy source to replace part of fossil fuels become the main direction of the current study of the marine engine.Nature gas was regarded as the main alternative fuel as its lower level of pollution.To find out how the three factors effect on the combustion and emission progress of the duel-fuel engine,the numerical simulation about the natural gas substitution rate,fuel injection parameters and combustion chamber on the diesel/natural gas dual-fuel engine,which was transformed by 4190 type marine middle speed diesel engine,were invested in this dissertation based on the combustion process model of dual-fuel engine established by using AVL-FIRE software.First of all,the two-dimensional geometric model of the combustion chamber is established by AutoCAD software.With the division of computational grid and the set of the initial parameters and boundary conditions,the combustion process simulation model of dual-fuel engine was established by using AVL-FIRE software general gas phase reaction module,by coupling the three-dimensional model of chamber with the chemical reaction kinetics.Secondly,the effect of the natural gas substitution rate,fuel injection timing and the spray angle on combustion and emission of the dual-fuel engine were studied with the single parameter rotatory method based on the simulation model.Five levels of natural gas substitution rate: 90%,80%,70%,60% and 50%;three levels of fuel injection timing: 700°CA?705°CA and 710°CA;three levels of spray angle: 140°?150° and 160° were selected to conduct the simulation of the performance of combustion and emission.The effect law of these parameters on pressure,temperature,heat release rate,the mass fraction of natural gas,NO and CO,as well as the distribution of physical fields in cylinder were analyzed according to the two-dimensional and three-dimensional results.Lastly,with the compression ratio fixed,two kinds of combustion chamber were designed.The influence of combustion chamber on gas velocity,turbulent kinetic energy in cylinder and the performance of combustion and emission of dual-fuel engine under the natural gas substitution rate of 90% and 70% were studied,which provides prediction and theory basis for the performance optimization experiment of the dual fuel engine.