Numerical Simulation And Experimental Investigations On The Combustion Process Of The Electronic Controlling CNG/Diesel Dual-fuel Engine

In recent years,alternative fuel has been the focus of research in the field of various industries because energy and environment problems is becoming more and more serious.As a clean and environmentally friendly alternative fuel,natural gas has a great advantage to be widely used.Because CNG/diesel dual-fuel engine which is modified from diesel engine can keep the same dynamic performance with diesel engine and obtain good fuel economy and emission performance,it becomes the hotspot of research and development in natural gas engine.In this paper,combustion process of CNG/diesel dual-fuel engine modified from 4102 diesel engine is studied,which has high theoretical significance and application value.In this paper dual-fuel engine indicator diagram and cyclical variations of pressure parameters were analyzed.Economy and emission performances of dual-fuel engine and diesel engine were also contrastively analyzed.In the part of simulation,then models was built up by using Pro/E,3D models was meshed in HyperMesh and dynamic grid was built in FIRE.According to the test results and the experience,the initial conditions and boundary conditions were selected.The combination of the experimental study and numerical simulation was adopted to focus on analyzing the excess air coefficient,fuel injection timing and injection pressure on combustion and emission characteristics of dual-fuel engine.Experimented study found that with the increasing of load,maximum cylinder pressure and COVpmax increased,then the indicated pressure is reduced,and COVpmi rose,as well as maximum pressure rise rate and COV(dp/d?)max were rising and then downward on the whole.Under 75% load the maximum pressure rate was greatest value.Under the heavy load economical efficiency of dual-fuel engine was better,but its NOX emissions was high,especially on the high speed operating working condition and NOX emissions were even higher than diesel engine.CO and HC emissions of the dual-fuel engine was much higher than the diesel engine.With the decreasing of excess air coefficient,NOX emission increased,but CO and HC emissions reduced.With the increasing of injection pressure,NOX emission increased obviously,as well as CO and HC emissions reduced.With the increasing of fuel injection timing,NOX emissions increased,but HC and CO emissions reduced.Simulation study was carried out to analyze problem about the higher NOX emission in the experiment under heavy load and high speed.Simulation study found that with lower excess air coefficient,the cylinder temperature,cylinder pressure and heat release rate of twin peaks all reduced,and the range of high temperature was narrower and later,as well as NO emissions were improved significantly.When the injection pressure increased,the cylinder temperature and cylinder pressure increased,and the first peak of heat release rate was on the rise,while the second peak was reduced,and high temperature was dispersed and larger,but NO emissions increased.With the increasing of fuel injection timing,temperature and pressure in the cylinder increased,and the second peak of heat release rate increased significantly,while high temperature area appeared earlier and bigger,and NO emissions increased.Therefore through reducing fuel injection timing and injection pressure,increasing the coefficient of excess air and other technical measures,NO emissions can be reduced.