Simulation And Optimized Design For CA4102 CNG Engine

Along with more attention attached on the energy safety and increasingly serious emission laws, the natural gas becomes an alternative fuel for its low emission, cheap price and rich resource.The natural gas engine has such merits: (1) high octane number, and better capability of anti-detonation, the thermal efficiency can be improved obviously for high compression ratio (2) excellent capability of start, for the fuel is gaseous without such process of evaporation and gasification as the gasoline or diesel fuel. (3) wide fire limit (4)the economic characteristics and environmental benefit can be improved farther by lean combustion technology for the low combustion temperature and low NOx emission.When natural gas used as engine fuel, it will occupy 10%-15%percentage of the intake charge, which will decrease the engine volume efficiency, as a result, the power performance dropped. The resonance boost was an efficient way to increase the power performance.The research in this paper was part of the project of development of natural gas engine CA4102, which was performed by the FAW(First Automobile Work) group and the college of JiLin university. We have established the engine simulation computation model by using GT-POWER software, and through the analog computation result compare to the test result, has confirmed the model validity and the accuracy.The influence rules of each parameter(total lengthen of the general pipe, inner diameter of the general pipe, lengthen and inner diameter of the manifold, volume of the resonance cavity) of the resonance system on the engine performance were got through the optimized design of the confirmation model. And 8 different improvement schemes were got by the choice and match of each parameter. One was selected as the better. The maximum torque has achieved 287N.m,the maximum power has achieved 80kW.In order to further improves the engine power, the article optimizes the valve timing on the base of optimized resonance system .Through the computation the maximum torque was enhanced by 30Nm,the maximum power enhanced by 8kW. Although the greatest power drops 2kW compared to engine before optimizingvalve timing, we obtain the higher torque at lower speed that is important to the engine power performance.Through the simulation to the natural gas engine, we provide the improved CA4102 gas engine power plan, the following conclusion as below.1.For the CA4102 natural gas engine, the intake manifold should not be long in consideration of layout, and the volume of the resonance cavity was mainly adjusted by adjusting the lengthen of main intake pipe. This plan selects the length of manifold is 570mm,the length of main pipe is 200mm.2.The bigger or smaller intake cavity was not suitable to get higher and proper volume efficiency. Because when it was bigger, it will become pressure stabling cavity without resonance function; when it was smaller, it will not meet the demand of intake charge under high speed. This plan selects the volume of intake cavity is 2L.3.The inner diameter of the main intake pipe should be larger for it decided the total air intake. The inner bore used in this plan was 70mm.4.The influence of resonance and resistance should be considered together when choosing the inner diameter of the intake manifold. The larger inner diameter will bring high resonance intensity, but the airflow speed was slow which will lead low airflow inertia kinetic energy. The smaller inner diameter can improve the charge coefficient in the large range of speed, but the smallest diameter should be limited in view of the resistance and threshold size of the intake port. This plan selects the inner diameter of manifold pipe is 40mm5.Reduce the camber of the pipe as much as possible to decrease the resistance of the pipe line. But the whole layout should also be considered to get a compact layout.6.Through the optimization, this plan selects the intake advance angle 22o,the intake closing angle changing 38o, intake advance angle from 12o to 22o from 48o to, the exhaust advance angle 42o, the exhaust lag angle 18o, namely the intake advance angle of original machine reduce 10o, the intake closing angle reduce 10o.7. Through the general optimization of the resonance air intake system and valve timing, finally we make sure intake system of CA4102 natural gas engine uses the plan as follow:The lengthen and inner diameter of the constant section manifold was 570mm and 40mm respectively, that of the general pipe was 200mm and 70mmrespectively, and the volume of the resonance cavity was 2L,the intake advance angle and lag angle was 22o and 38o, the exhaust advance angle and lag angle is 42o and 18o respectively.Using this plan, the engine maximum torque compared to original machine enhancing by 11.2%, has achieved 295N.m, the greatest power compared to original machine enhancing by 11.4%, has achieved 78kW.