Study On Combustion And Emission Characteristics Of Controlled Auto Ignition Gasoline Engine

Environmental pollution and energy scarcity are two major problems that beset countries around the world today.Controlled Auto Ignition-CAI combustion technology has the advantages of high dilution tolerance,good combustion isopvolubility,low adiabatic combustion temperature,high thermal efficiency,and low nitrogen oxide emissions.It has become a research hotspot in the field of internal combustion engine in recent years.However,CAI combustion is still faced with problems such as narrow combustion operation range and difficult to control combustion phase,which limit its practical application.This paper analyzes the influence law of different control parameters on CAI steady-state combustion and emission characteristics,and conducts sensitivity analysis of each control parameter based on orthogonal experimental design.It is very important to optimize the CAI combustion process by cooperating with the control parameters.In addition,since the vehicle is in the acceleration,deceleration and load transients for most of the time in the process of driving,in order to consider the practicability of CAI engine,the change of the combustion and emission characteristics in the transient condition of CAI engine is studied.This research work is very necessary and important for CAI engine from theory to practice.The main work of this paper is as follows:1.Based on a naturally aspirated,four-stroke single-cylinder diesel engine ZR180,a CAI gasoline engine test platform was built after a series of modifications,on which gasoline SI and CAI combustion modes could be carried out.Firstly,the realization of CAI was explored.At the same time,the simulation model of CAI gasoline engine GTPower is built,and the simulation model is checked by the test data obtained from the bench,and the accuracy of the simulation model is verified.2.The influence of control parameters(intake temperature,intake pressure,excess air coefficient,exhaust valve timing,intake valve timing)on combustion and emission characteristics of CAI gasoline engine is studied by simulation.The results show that:when intake temperature increases,CA50 advances,IMEP decreases,NOx emission decreases,and CO emission increases.When the intake pressure increases,the combustion phase is advanced,the combustion speed is accelerated,and the IMEP is increased.For excess air coefficient,CAI combustion state is optimal when λ is about1.02,and the maximum in-cylinder pressure peak and IMEP appear.When the exhaust valve closes late,the peak pressure in the cylinder increases,the CA50 advances,and the combustion speed is accelerated.When the intake valve is opened late,the peak pressure in the cylinder first increases and then decreases,and CA50 first advances and then delays.3.Based on the orthogonal test design,the sensitivity analysis of the control parameters is carried out.The results show that: exhaust valve timing and intake pressure have the most obvious influence on the load,and intake temperature has the least obvious influence on the load.Exhaust valve timing and intake pressure have the most obvious influence on CA50,while intake valve timing has the least obvious influence on CA50.4.Based on the test,the motion characteristics of the valve are tested and analyzed.The results show that the transient response speed of the exhaust valve is fast and the response process is accurate.The response is ideal.The combustion during the switching process is stable.5.Simulation was used to analyze the effects of different transient times and valve parameters(intake valve lift,intake valve timing,exhaust valve lift)transient times on combustion and emission characteristics under transient conditions in CAI mode.The results showed that: Under loading conditions,with the increase of transient time,intake lag is gradually improved,the maximum deviation of torque and IMEP is reduced,and the time for NOx emission to reach stability is shortened.Under load reduction condition,with the increase of transient time,the deviation between the intake response speed and the response speed of the circulating oil supply gradually decreases,the time for the internal EGR rate to reach the stability is gradually shortened,and the change severity of the maximum temperature and peak cylinder pressure in the cylinder gradually slows down.Increasing the intake valve lift transient time can improve the intake response speed,and thus the air-fuel ratio response speed.Increasing the inlet valve timing transient time will slow down the intake response speed and the air-fuel ratio response speed.Increasing the exhaust valve lift transient time has the greatest impact on the internal EGR rate,which will slow down the internal EGR rate response,and then affect the transient process.6.The response characteristics of CAI combustion when the engine speed changes are studied.The results show that: In the CAI combustion mode zone,when other control parameters are unchanged and only the engine speed is changed,CAI combustion is not sensitive to the change of the speed and the combustion state does not change with the change of the speed.There is no misfire or other abnormal combustion in the process of engine speed conversion.The combustion transition is stable and can ensure stable torque output.