Study On Combustion And Emission Characteristics Of Hydrogen Direct Injection Engine Coupled With Internal EGR

Nowadays,the automotive industry is in a chaotic period of energy diversification,power diversification and technology system diversification.Pure electric vehicles,hybrid electric vehicles and fuel cell vehicles have sprung up.As the traditional internal combustion engine,although it still occupies the absolutely dominant position of automotive power,the challenges from energy,environment and transportation are increasing day by day.The most stringent emission regulation CN6 in history requires automotive engines to be more efficient and clean.Traditional gasoline engines have low combustion efficiency and bad combustion stability under medium and low loads,especially CO and HC emissions are difficult to control below the regulation limits.The paper adopts large EGR rate coupled with hydrogen to realize the load adjustment of gasoline engine to improve the power performance,combustion stability under medium and low loads,and reduce CO,HC and NOx emissions at the same time.Firstly,the engine control system is developed by means of d SPACE tools,including the analysis of the principle of DVVT control system,the hardware design of DVVT control system,the Simulink modeling of DVVT system,the MIL test and the calibration in Control Desk NG software.Then a one-dimensional engine simulation model is built by GT-Power software,the model is calibrated according to the experimental data.The DOE module in the software is ultilized to find the mapping relationships between different IVO(Intake Valve Open),EVC(Exhaust Valve Closed)timing and internal EGR rate under low and medium loads.Finally,the effects of different internal EGR ratios on combustion,power and emission characteristics of gasoline engine under three modes of PFI(Port Fuel Injection),PFI+GDI(Port Fuel Injection plus Gasoline Direct Injection)and PFI+HDI(Port Fuel Injection plus Hydrogen Direct Injection)are completed in the test cell.The test results and main conclusions are as follows:(1)Under low load,when the internal EGR rate is between 14% and 47%,with the increase of the internal EGR rate,the maximum cylinder pressure,maximum heat release rate and maximum temperature all decrease,combustion center is delayed gradually,combustion duration is prolonged,IMEPn,FMEP absolute value,engine net torque are increased respectively,and Co VIMEP is increased,CO emission decreases first and then increases,HC emission increases gradually,and NOx emission decreases gradually.Large internal EGR ratio in PFI mode causes serious incomplete combustion and misfire issues,PFI + GDI mode improves the combustion stability,while PFI + HDI mode accelerates the combustion speed significantly.Compared with the original engine state,the IMEPn increases 20% among which the PMEP contribution is 7.5% by adopting 37% of the internal EGR rate coupled with 10% of hydrogen,the net torque of engine increases 30.5%,the Co VIMEP is reduced from 1.3% to 0.69%,and CO,HC,NOx emissions are reduced 66%,12% and 85% respectively.(2)Under medium load,when the internal EGR rate is between 7% and 28%,with the increase of the internal EGR rate,the trend of change in combustion characteristics under low load is nearly the same as PFI and PFI+GDI modes under medium load,but in PFI+HDI mode,maximum in-cylinder pressure and maximum in-cylinder temperature gradually increase with the increase of internal EGR rate,maximum heat release rate gradually decreases,combustion center and combustion duration are delayed within 2 CA.Under the three modes,IMEPn,FMEP absolute value and engine net torque increase with the increase of internal EGR rate while Co VIMEP decreases,CO emission decreases at the beginning and then remains unchanged,HC and NOx emission decreases gradually.The combustion speed of PFI + HDI mode is faster than PFI + GDI and PFI modes.Compared with the original engine,IMEPn increases 8.5% among which PMEP contribution is 3% under 28% of the internal EGR rate coupled with hydrogen mode,the net torque of engine increases 11%,the Co VIMEP of engine is reduced from 1.07% to 0.75%,and the CO,HC,NOx emission is reduced by 22%,34% and 37% respectively.(3)With the increase of internal EGR rate,the optimum ignition advance angle MBT increases.The MBT increased significantly after hydrogen was added into the cylinder.The bigger the engine load,the smaller the optimum ignition advance angle MBT.The larger internal EGR rate and the optimum ignition advance angle under medium load can achieve better dynamic and emission performance than the smaller internal EGR rate,and adding hydrogen can further expand the ignition range with the best combustion,stability and emission characteristics.However,the combustion cycle fluctuation rate is too high under large internal EGR rate at low load,hydrogen can improve flame kernel stability and combustion stability of engine,but the optimal ignition region is smaller than that of medium load.Under medium and low loads,the use of internal EGR coupled with hydrogen in cylinder and the optimum ignition advance angle can achieve better engine power,fuel economy and emission characteristics than conventional combustion mode engines,which has a positive significance for the implementation of the national policy of promoting more efficient and clean internal combustion engines.