Research On Influence Of Valve Timing On The Performance Of Turbocharged PFI Gasoline Engine

The low torque output and the slow accelerate response are the defects of engine performance at low speed, full load. At part load, the thermal efficiency of traditional engine is low, the fuel energy can’t be fully used and engine pumping losses is higher. According to the above problems, based on the turbocharged engine model, this paper researched the influence of valve timing on the performance of engine, adjust the phase distribution, analysis of the low power output characteristic and fuel economy under partial load the potential ability of ascension.Firstly, under the working condition of low speed, full load, the output torque of PFI engine can’t meet the demand of performance. Equipped with the turbocharger is a good way to improve the defect. By adjusting the angle phase of the valve, the inlet and exhaust valves can open at the same time, it’s valve overlap period, inlet and exhaust pressure is different, the scavenge can be realized. Because of the scavenging, burned mixture gas discharge outside the cylinder, the process of air cylinder improved, increase the fresh charge quantity, the volumetric efficiency increase, the supercharger response speed improved. At full load of 1200 rpm, when the IVO = 30 ° CA, EVO = 20 ° CA, the engine output torque is the largest. Valve overlap angle must be in reasonable range, otherwise the fresh mixture will be expelled from cylinder, thus affect engine thermal efficiency and power output. When the valve overlap angle exceeds 50 ° CA, engine torque fells sharply.Secondly, at partial load conditions, based on the principle of Atkinson, researched the valve timing affects the fuel economy. At the speed of 1600 rpm, with the same output MEP, the engine’s fuel consumption gradually reduced with the increase angle of late intake valve close, especially the average pressure less than 6 bar, the specific fuel consumption significantly reduced with the later closed of inlet valve. At part load, only by relying on the inlet valve adjustment, full range load control can’t be achieved, the full range of load control can be achieved by using throttle and intake valve in coinstantaneous. At part load, at the speed of 2400 rpm, 2800 rpm, 3200 rpm, 3600 rpm, the intake valve close angle delay in 70 °CA, 85 ° CA, 100 ° CA on the basis of the original 55 ° CA, with the throttle opening in 20%, 40%, 60%, 80%, the output torque decreased by 3%, 8.6% and 16.2% respectively and the specific fuel consumption was reduced by 0.3%, 0.5% and 1.6% respectively. At the high speed condition, only with the delay of intake valve close angle when the MEP beyond 10 bar, the consumption will not change, when the MEP range from 4bar to 10 bar, the fuel consumption fluctuate in 1.3 percent. Applicated at high speed, full load condition, Atkinson cycle cannot improve the fuel economy, but the power output is decreased.