Study On The Influence Of Variable Valve Lift On Combustion And Emission Property Of Methanol Engine

With growing global concerns about fossil fuel supplies and extreme weather events,the search for renewable carbon-neutral fuels has become key to addressing the energy and environmental issues caused by internal combustion engines.At the same time,the application of new technologies on alternative fuel engines to improve engine combustion and emission performance is bound to become an important direction of future internal combustion engine research.In order to further enhance and improve various performance of methanol engine,this study used pure methanol as fuel,equipped with a variable valve lift mechanism independently developed by our research group on a single cylinder test prototype of inlet injection spark plug ignition transformed by Changchai ZR180,and operated at 1200r/min and 27.75mg/cycle fuel injection rate.The effects of various inlet and exhaust valve lift strategies on engine combustion and emission performance were investigated by experiments under equivalent ratio combustion and air dilution combustion respectively.In addition,GT-power software was used to build a onedimensional simulation model for supplementary analysis of test parameters,and simulation analysis was carried out for the variable valve lift mechanism developed by our research group,and the influence of intake and exhaust valve lift,timing and duration on engine performance was studied,providing theoretical support for the next optimization of the variable valve mechanism.The application of variable valve lift technology in ignited methanol engine is more deeply understood.The main conclusions are as follows:1.The effects of nine valve control strategies on the performance of methanol engines were compared under equivalent combustion conditions.The results show that the internal EGR rate decreases with the increase of valve lift.Compared with the original engine state,the indicated thermal efficiency,cycle variation,combustion duration and turbulent kinetic energy increase with the increase of internal EGR rate.Heat transfer loss and pump gas loss decrease.Under the optimal strategy,the torque of methanol engine increased by 4.8%,the fuel consumption rate decreased by5.69%,the NOx emission decreased by nearly 30.86%,the CO emission decreased by 5.6%,and the improvement degree of HC emission was not obvious.2.Under the condition of air dilution combustion,the influence of traditional throttle control strategy a and non-throttle lower intake valve control strategy b on engine thin burn performance is compared.With the increase of excess air coefficient,Under strategy a,the turbulent kinetic energy in the cylinder increases,while under strategy b,the turbulent kinetic energy decreases.When the excess air coefficient is 1.3,the indicated thermal efficiency under both strategies is the highest.The maximum torque,maximum pump loss,minimum fuel consumption,THC and CO emission under strategy b increased by 0.89%,decreased by 37.5%,2.66%,7.68% and 7.1%,respectively,compared with the corresponding data under strategy a.3.With the delay of the opening time of the intake valve,the internal EGR increases first and then decreases,the pump gas loss and heat transfer loss increase,and the exhaust gas loss and indicated thermal efficiency decrease.With the increase of the intake valve opening duration,the pump gas loss first decreases and then increases,and the indicated thermal efficiency first increases and then decreases.Heat transfer loss and NOx emission increase accordingly.The internal EGR rate and exhaust loss are reduced.With the increase of intake valve lift,the internal EGR rate,exhaust loss and pump gas loss decrease under the same torque.Heat transfer loss,indicating an increase in thermal efficiency.4.When the maximum lift of the exhaust valve increases from 3.5mm to 6.6mm,the heat transfer loss increases,and the internal EGR rate,pump gas loss,and exhaust loss decrease.It is also found that when the maximum exhaust lift is 6mm,the methanol engine can achieve an indicated thermal efficiency of up to 30.5%.When the exhaust valve closing time is 330°CA ATDC,the internal EGR rate increases when the exhaust valve opening duration increases from 120°CA to 160°CA.Exhaust loss increases first and then decreases,pump gas loss,heat transfer loss,indicating fuel efficiency decreases.In general,whether it is for the intake valve or the exhaust valve,the use of relatively high valve lift,valve opening timing as much as possible to keep the same or slightly delayed profile is basically conducive to the improvement of its performance,which has guiding significance for the further improvement of the variable valve lift mechanism used in this paper.