Analysis Of Variable Valve Actuation In High Geometric Compression Ratio Engine

Due to the influence of engine knock,the thermal efficiency of gasoline engine is greatly restricted by its geometric compression ratio.The application of variable valve Actuation can change the effective compression ratio of the engine in miller cycle and then improve the geometric compression ratio of the engine.My thesis topic is Analysis of Variable Valve Actuation in High Geometric Compression Ratio Engine.Firstly,I designed the early closing control strategy of the inlet valve and the late closing control strategy of the inlet valve under different loads at 2000r/min for high geometric compression ratio engine by GT-Power.I analyzed the influence of variable valve actuation on heat transfer loss,exhaust loss,pumping loss and friction loss of the high geometric compression ratio engine.Then I summarized the influence of the engine’s power performance and fuel economy.I also analyzed the advantage of using variable valve actuation to suppress knock.The results show that as the angle of early closing of the inlet valve increases using early closing control strategy of the inlet valve can decrease the heat transfer loss,increase the exhaust energy loss,increase the indicating work,decrease the pumping loss,decrease the friction loss slightly and increase the effective work.The control strategy with the largest early closing angle of the intake valve has the best power performance and fuel economy.Using late closing control strategy of the inlet valve is beneficial to reduce the heat transfer loss of energy,but the exhaust energy loss becomes larger and can increase the indicating work.It also can decrease the pumping loss,decrease the friction loss slightly and increase the effective work.The control strategy with the maximum intake valve lift has the best power performance and fuel economy.Under heavy load,early closing control strategy and late closing control strategy can reduce the occurrence of knock.Then according to the method of designing the variable valve control strategy for each load of the engine at 2000r/min,I designed the early closing control strategy of the inlet valve and the late closing control strategy of the inlet valve under different loads at other speeds.I calculated the power performance and fuel economy of the engine under each control strategy and selected the optimal variable valve control strategy under each operating condition.It is found that the influence of different control strategies on the engine performance is similar under different operating conditions.Compared with the throttle control strategy of the original engine,the early closing control strategy of the inlet valve has achieved a certain degree of improvement in power and fuel economic performance.When the inlet valve is closed at the earliest time,the early closing control strategy of the inlet valve has the best fuel economic and power performance under different working conditions.The late closing control strategy of intake valve with the highest inlet lift is the optimal one.It can achieve better performance than the early closing control strategy of intake valve under some low speed and heavy load conditions,while the performance under some high speed conditions is lower than the throttle control strategy of the original engine.When the engine is under high speed and small load,the late closing control strategy of inlet valve cannot be adopted due to the limitation of engine physics.Finally,in order to explore the effect of high geometric compression ratio engine using variable valve actuation in practical application,I calculated the constant fuel consumption and NEDC cycle fuel consumption of the high geometric compression ratio engine loaded with variable valve control strategy and throttle control strategy respectively.The calculation results show that the fuel consumption of the engine with high geometric compression ratio using the variable valve control strategy is significantly lower than that using the original throttle control strategy.When the vehicle speed is 90km/h,the fuel consumption of the variable valve control strategy is reduced by 0.4L per 100 km compared with the original engine.When the speed is 120km/h,it decreases by 0.3L per 100 km.The fuel consumption of the NEDC cycle decreased by 6.9%.