| Whether from the perspective of national energy security,energy saving,emission reduction,carbon reduction,etc.,internal combustion engines are required to seek alternative fuels that can be implemented and optimize in-flight purification technology.Methanol as an alternative fuel combustion carbon emissions are relatively less,combustion heat efficiency is higher,good explosion resistance,fast combustion speed,better lean combustion performance,lean combustion can further improve thermal efficiency,obtain better fuel economy,but lean combustion limit is subject to cycle changes,so it is also necessary to improve the cylinder airflow movement,so as to improve combustion speed and combustion stability,further broaden the thin combustion limit of methanol engine.This paper is based on a 2.0-liter four-cylinder SIDI engine and CONVERGE software is used to carry out related tests and simulation studies.1.The lean combustion characteristics of methanol under different excess air coefficients,speeds and loads with different intake flap openings were studied experimentally,and the lean combustion characteristics of methanol and gasoline under different excess air coefficients at 45°of intake flap opening were compared and studied.The experimental results show that the cycle variation increases with the increase of excess air coefficient,the increase of speed and the decrease of load,and the combustion speed under different excess air coefficients,speed and load can be better accelerated when the air intake flap opening is 45°,the cycle change can be better suppressed,the cycle change can be better suppressed,and the lean burn limit of methanol engine can be broadened.It can optimize the combustion process of methanol engine,increase the combustion temperature,reduce CO and HC emissions,but will relatively increase NO_X emissions,and effectively improve IMEP and indicator thermal efficiency when severe lean combustion(excess air coefficient value greater than or equal to 1.5);when the total intake air and excess air coefficient are the same,the IMEP and indicated thermal efficiency of methanol lean combustion are much greater than gasoline,the maximum difference of IMEP is about 0.6bar,and the maximum difference of the indicated thermal efficiency is 6%.The HC and NO_X emissions produced by gasoline combustion are significantly larger than those of methanol;At the same time,it can improve the IMEP and indication thermal efficiency of methanol engine at various speeds,broaden the optimal load range of methanol engine operation,and significantly improve the indicator thermal efficiency at small loads.The performance of all aspects is similar when the opening of the intake flap is 15°and 0°,while the reverse tumble in the cylinder is generated at the opening of the intake flap at 30°,and the two cancel each other out,so the performance in all aspects is relatively the worst.2.The effect of changing the intake flap and the intake guide plate alone on the lean combustion characteristics of methanol engine was studied,and it was found that compared with other intake flaps,flap 2 can greatly improve the tumble intensity in the cylinder,increase the turbulent kinetic energy,improve the quality of the mixture,accelerate the combustion speed,increase the cylinder pressure,the combustion temperature in the cylinder,reduce CO and Soot emissions,but the final improvement effect on IMEP and indicator thermal efficiency is not obvious,while the flap 3,flap 4 and guide plate 2,Guide plate 4 has a better effect on IMEP and indicator thermal efficiency,so to improve IMEP and indicator thermal efficiency,we cannot overly pursue greater tumble strength.Changing the intake flap alone has a more obvious effect on enhancing the tumble strength and turbulence strength in the cylinder than changing the intake guide plate alone.Enhancing the tumble intensity in the cylinder can ultimately improve the turbulence intensity at the ignition time,accelerate the combustion speed,improve the uniformity of the mixture,reduce the peak mass of CO and Soot,and improve the power and economy of methanol engines.The structure of the left high and right low of the original flap will affect the movement of the airflow in the cylinder,resulting in the formation of obvious concentration zones of the mixture,which will inhibit the improvement of the uniformity of the mixture to a certain extent.3.The effect of optimizing the cross-coupling of the intake flap and the intake guide on the lean combustion characteristics of methanol engine was studied,and it was found that:compared with other cross-coupled deflectors,the flap 4 guide plate 4 has a better effect in improving the tumbling intensity and turbulence intensity in the cylinder,which is conducive to the formation of large-scale tumbling vortex in the cylinder,the best uniformity of the mixture in the cylinder,the fast combustion speed,the good performance of CO and Soot generation,and the largest IMEP and indicator thermal efficiency.The in-cylinder flow characteristics,combustion characteristics,emissions,etc.of the flap 4 guide plate 4 are better than the original air deflector,its IMEP is increased by about 0.106bar,the indicated thermal efficiency is increased by about 0.79%,and it can well solve the problem of mixing gas partition caused by the original flap,greatly improve the uniformity of the mixture,and at the same time obtain higher power and economy compared with changing the structure of the intake flap and the intake guide plate separately.4.The applicability of the optimized intake deflector plate under different speeds and loads was simulated and studied,and it was found that optimizing the deflector flap 4 can effectively accelerate the combustion speed under each speed and load,increase the cylinder pressure,heat release rate and cylinder temperature peak and advance peak phase,and the lower the speed or the larger the load,the larger the peak cylinder pressure and temperature in the cylinder.It can effectively improve the power and economy of methanol engine when the speed is greater than1000r/min or medium and small load,and the lifting effect is most obvious at 1500r/min or 50%load.CO and Soot generation peaks can be effectively reduced at various speeds and loads,but the total mass of NO_X generation and the generation peak of formaldehyde of intermediate products will be slightly increased. |
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