Experimental Research On The HCCI Combustion Process Of Hydraulic Free Piston Engine

Hydraulic free piston engine is the combination of internal combustion engine technology, modern hydraulic technology and electronic control technology. With the increasingly serious energy crisis and environmental problems, free piston engine, which has great potential in the thermal efficiency and emissions, mounting attention. The present thesis combined HCCI combustion process with hydraulic free piston engine, aimed to mutually draw on each other's strength and make up deficiencies. A series of HCCI combustion experiments have been conducted to improve engine thermal efficiency with different fuels in the hydraulic free piston engine, to study the inner relationship and influence law between fuel properties, control parameters, operation parameters and the engine performance parameters, and to explore ways to improve the thermal efficiency of HCCI combustion in the hydraulic free piston engine.The author firstly designed and improved the test system, transformed the opposed-piston prototype into the single piston hydraulic free piston engine, and optimized the high pressure solenoid valve to increase the opening pressure without affecting its response time. The HCCI combustion experimental research of ether was then conducted to, analysis the influence of different cylinder heating temperature, fuel mixing uniformity, equivalent ratio, compression ratio on ether's HCCI combustion. The results showed that the indicated efficiency reached the highest rate of 46.57% with the equivalent ratio 0.3 and the compression ratio 14.22. In the third study, the HCCI combustion experimental research of n-heptane was run to analysis the influence of different equivalent ratio, compression ratio on n-heptane's HCCI combustion. The results showed that the indicated efficiency reached the highest rate of 44.63%, with the equivalent ratio 0.3 and the compression ratio 14.22. Besides, the HCCI combustion experiment of low cetane number fuel, gasoline and methanol was conducted to explore the feasibility that the hydraulic free piston engine can burn the low cetane number fuel or not. At last, the CFD simulation on the HCCI combustion process of methanol was studied, the results showed that deflagration in the process of methanol HCCI combustion was due to the reason of excessive heat release rate, which induced the vibration of cylinder pressure wave and leaded to the multiple reflections in the space.The thesis has realized single time high efficiency operation with different fuels in hydraulic free piston through a series of experimental study, and verified the feasibility of HCCI combustion process with different fuels in the hydraulic free piston engine. The inner relationship between engine performance parameters and control parameters have been discussed, which laid the foundation for prototype's continuous stable work in the future.