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The domestic vehicle production increases year by year, in 2009, China has beyond America become the biggest country in vehicle production and consumption in the world. However, there is great gap between independent brand and foreign brand. It has become the bottle neck of expansion of domestic vehicle company to develop engine with intellectual property rights, especially in the power and fuel economy. Nowadays, in the background of calling for low carbon economic, energy saving becomes more and more important.This paper presents 2.0L and 1.8L SI engine design on the basis of 2.4L SI engine platform of one native company, realize diversification of engine type. At the same time, optimization research has been done on inlet, compression ratio, valve timing and intake manifold geometry respectively, as a result, improving the power and fuel consumption of 2.0L and 1.8L SI engine.Firstly, using the way of CAE, Thermal dynamic calculation had been carried out to predict the power and fuel economy, balance different inlet and compression ratio scheme, it came the result that using wide flow area inlet and relative high compression ratio can make better engine performance; besides, valve timing and inlet geometry’s affection on engine had been researched, and it had came the result that adjusting valve timing and intake pipe length and diameter can greatly increase low speed torque.Secondly, a 3D model had been made on the area of inlet and cylinder using CFD tool AVL-FIRE. Calculation and analysis had been take on the inlet and in-cylinder flow field, it came out the result that using the inlet with wider flow area can better construct intake process, form a flow field good for combustion, so power and fuel economy is improved.According to the result of simulation on 2.0L and 1.8L SI engine, confirming the design on inlet, compression ratio, valve timing, and intake manifold geometry etc, which can greatly affect the performance of engine. Engine with new designed inlet and compression ratio has been trial-produced. According to the test result, power per liter of 2.0L SI engine is 13.2% higher than 2.4L SI engine, average fuel consumption is 9.96L/100Km, emission level accords with state 4 emission standard, while 2.4L SI engine has only accorded with state 3 emission standard. After this test, there will be new prototype with VVT and plastic intake manifold optimized according to this research.
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