Preliminary Analysis On The Fuel Economy Of Compound Engine

To achieve the precise control of HCCI ignition, the compound engine ignited by the high-pressure gas compression was proposed. The engine that was added a high-pressure gas tank uses a compound system with low compression ratio, high pressure-rise ratio and high-expansion ratio, and the cylinders were divided into power cylinder and compression cylinder. In an early time the fuel was injected into the cylinder to make sure the homogeneous mixture can be achieved, through setting the smaller compression ratio the temperature was ensured not so high that the mixture can not be ignited without the external additional heat source. At the end of compression some high-pressure gas was injected into the cylinder, which was mixed with the mixture in cylinder for the second time. Utilizing high-pressure gas injection to ignite the mixture in the cylinder can achieve the homogeneous pre-mixed compression combustion.Using one-dimension simulation software AVL-Boost established the compound engine power cylinder model on middle conditions, this model can achieve the precise control of the gas injected into the cylinder. Besides, utilizing thermal dynamic formulas sets up the compression cylinder model of compound engine when throttle loss and hear release loss were both considered, the thermal efficiency and fuel economy formulas for compound engine were proposed in the end.The model was used to make a comprehensive analysis about all kinds of factors that influence the compound engine thermal efficiency at different speed on the middle conditions by calculating and optimizing. The factors included the pressure of high-pressure gas tank, the injecting duration of high-pressure gas, the injection timing of high-pressure gas, the engine geometric compression ratio, the ignition timing, the high-pressure gas nozzle shape, the high-pressure gas jet valve and the combustion duration.The results show that at middle and high speed the fuel economy of compound engine was better than the original engine, and the thermal efficiency was increased by 8%, so that the fuel economy was increased by more than 5%.