| Accompanied by serious problems of energy and environment, the automobile industry has put forward more strict legislation for economics and emissions of vehicle engines. The study of Miller and Atkinson cycle has currently become a research focus for their high efficiency. In this paper, test and simulation method both have been used to study performance of the engine with low compression and high expansion ratio through machinery.First, according to the invention called dead center changing with phase, get the motion law of the eccentric shaft, which is the key component of the target engine. From the standpoint of crank-link mechanism dynamics, conduct theoretical stress analyze of the eccentric shaft and find the motion law suggested in the invention is one of the possible motion laws. So piston position has been derived and get its formula S f(L, R,Φ,e), which is useful for the following research.Then, perform load characteristic experiments and vibration test on a test prototype transformed from a CA4GA1 engine. The experimental results show that, under MBT, fuel economy of the test prototype is significantly improved compared with original engine. However, the motion law of eccentric shaft is not certain, so whether the improved fuel economy benefits from the eccentric shaft or not cannot be confirmed. In addition, the vibration and cycle to cycle variation of the test prototype are far more than the standard values, which limit its practical application.In order to verify whether the economic theory is right which was put forward by the invention called dead center changing with phase, a one-dimensional model of a single-cylinder engine with low compression ratio and high expansion ratio is set up by GT-power software and the model of original engine is also established. And analyze the feasibility of the model from the maximum cylinder pressure and position. The simulation results show that:(1) Under low speed and light load, the fuel economy of the prototype deteriorated.with increasing of load, the fuel economy is slightly improved at heavy load than the original machine. At the speed of 2000 r/min, BMEP 9bar, the fuel consumption of the prototype is lower than the original machine around 0.6 g/(k W · h). The condition of middle speed and light load is similar to low speed and light load one, but in the condition of middle speed and middle-heavy load, the fuel economy of the prototype is improved, and is obviously than low-speed condition. At the speed of 4000 r/min, BMEP 9 bar, the fuel consumption of prototype is about 2 g/(k W · h) lower compared to the original machine. Fuel economy performance of Prototype at high speed is worse than original engine under all partial load conditions. In conclusion, the prototype has oil saving potential under the condition of low- middle speed and middleheavy load.By choosing two typical operating conditions for the improvement and deterioration of the prototype economy, the reasons of fuel economy improvement and deterioration are analyzed from two aspects of thermal balance and mechanical loss. Analysis results show that, at the condition 4000r/min, BMEP 9bar, cooling loss ratio of the prototype accounted for the total input energy is 1.3% more than the original engine, but the exhaust loss is 1.7% less than the original engine. And FMEP and PMEP of the prototype are more than original engine. But the benefit caused by the reduction of the exhaust loss of the prototype is more than the deficit caused by the loss of cooling loss, FMEP and PMEP. So the fuel economy of prototype is improved under this condition. On the contrary, the condition of 2000r/min, BMEP 2bar, the benefit resulting from the reduction of exhaust loss of the prototype machine can not compensate for the loss caused by the increase of other losses, so the fuel economy of the prototype is worse than that of the original engine. The PMEP of both two conditions are 0.1bar higher than the original machine, which has a negative impact on fuel economy of the prototype. |
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