| With the sustainable growth of the automobiles,the environmental pollution caused by energy consumption and exhaust emissions cannot be ignored.In order to meet stringent fuel consumption regulations and emission regulations,new technologies were developed by auto companies and related research institutions.For instance,the GDI combining with the variable valve technology and turbocharged technology can not only ensure dynamics performance,but also improve the fuel economy.At partial loads,EGR technology can increase the intake pressure,reduce the intake loss,and it can reduce the tendency of knock by decreasing the maximum pressure in-cylinder and reduce emission.In this paper,1.5-liter displacement GDI engine was choosed and one-dimensional calculation model of the engine was built by GT-Power software.The GT-Power model of this engine was verified using experimental data.Several cam profiles were designed based on the engine of Otto cycle,its performance was researched by the application of Miller cycle and EGR technology;Combined with one-dimensional simulation results,the three-dimensional intakechamber model of the engine was built with the CONVERGE software and it was verified using the experimental data.The influence of original engine,EIVC,LIVC on the air-fuel mixture,combustion and emission were investigated and analyzed.The main work and conclusions are as follows:(1)The partial load and full load conditions of 1000r/min,2000r/min,3600r/min and the rated condition were chosen to study the performance of GDI engine with different Miller cycles.The results showed that under partial load conditions,the Miller cycle could improve fuel economy by reducing pumping loss,increasing intake density,and reducing combustion temperature.The Miller cycle had a significant effect on improving the fuel economy of the engine under 1000r/min,100% load.Besides,the fuel economy had an obvious improvement with the increasing of Miller degree within a reasonable range.When the Miller degree was-29°CA for EIVC,the fuel consumption had a significant reduction of 10.5%,but the Miller degree continued to increase,the fuel consumption increased gradually.The effect of Miller cycle on fuel economy was not obvious at the speed of 2000r/min to 3600r/min.Miller cycle made fuel economy worse at 5600r/min.(2)The effects of Miller cycle combined with EGR on engine performance were investigated at 2000r/min and 50% load.The results showed that EGR had a limited improvement on fuel economy for EIVC.For LIVC,the fuel consumption had a maximum improvement at 7% EGR rate.Meanwhile,the fuel consumption decreased by 1.3% compared the original engine with the same EGR rate;and reduced by 3.2% compared with original engine without EGR.(3)Based on the one-dimensional calculation results,at 2000r/min,50% load,and Miller degree was ±58°CA.The velocity field,turbulent kinetic energy and equivalence ratio distribution in cylinder were analyzed,it could be known that LIVC could significantly enhance the turbulent kinetic energy,improve the air-fuel mixing,and be beneficial for combustion.For EIVC,the turbulent kinetic energy decreased obviously,it was lower than LIVC.The results showed that the combustion phase of LIVC was more reasonable compared to EIVC and original engine,and its maximum pressure in cylinder was increased while the combustion temperature was lowered,so that the soot emission was reduced.For EIVC,as the turbulent kinetic energy decreased,the combustion process of cylinder slowed down,the combustion temperature decreaseed significantly,and HC emission increased significantly.(4)Adding 7% EGR to LIVC and the original engine,the influence of Miller cycle combined with EGR on the combustion and emission were investigated.The results showed that EGR could effectively improve combustion process and reducethe maximum pressure and temperature in cylinder.This was beneficial to reduce the tendency of knock and made it possible for improving geometric compression ratio and optimizing combustion. |
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