Study On The Effect Of Combustion Intermediate Products In Residual Gas On Gasoline HCCI Combustion Auto-Ignition

With the deterioration of environmental pollution and the shortage of oil reserves, energy conservation and pollution reduction becomes the most urgent demand. And Gasoline HCCI combustion has drawn extensive attention from world-wide internal combustion engine field due to its significant improvements in efficiency and reduction of NOX emissions. However, during the process of engineering practice, there are still several technology problems, especially the effective control of auto-ignition timing in HCCI combustion. It is known that controlling the auto-ignition timing by adjusting component and concentration of the mixture gas could have some attractive performance such as quickly response, easy operation and individual control between cylinders. Therefore, in this research, the effect of different components of the intermediate products on gasoline HCCI auto-ignition is investigated by simulation and experiment.The experimental results proved that there were probably some active species which can influence the auto-ignition of HCCI combustion in residual gas. In-cylinder gas during compression stroke of HCCI combustion using internal residual gas recirculation strategy was obtained by self-developed in-cylinder sampling system and analyzed by gas analyzers. The analysis results indicated that there were many kinds of carbonyl compounds in residual gas but only the concentrations of formaldehyde and acetaldehyde were high while the concentrations of other carbonyl compounds were lower than 1 ppm. The concentrations of ethylene, methane and formaldehyde measured by FTIR were almost above 200 ppm, the concentrations of propylene, acetylene and acetaldehyde were between 100 ~ 200ppm, while that of alcohol, 1,3 butadiene and ethane were lower than 100 ppm.The effects of different components of the intermediate products on gasoline HCCI auto-ignition were simulated with CHEMKIN and 4-component gasoline surrogate chemical kinetic mechanism. Compared to the simulation result without any intermediate products, the advanced crank angle of HCCI combustion auto-ignition timing with 200 ppm addition of different component of intermediate products are: acetylene (1.5°CA), formaldehyde (1°CA), ethylene ( 0.5°CA), ethane (0.5°CA), methanol (0.5°CA), ethanol (0.5°CA), acetaldehyde (0.5°CA), methane (0°CA), propylene (0°CA), carbon monoxide (0°CA), 1,3 butadiene (-1°CA).Experimental results also showed that fuel reforming can advance the auto-ignition timing of HCCI combustion. With in-cylinder gas analysis, it is shown that the concentrations of total intermediate products increased with fuel reforming, and the components of most increase were methane, acetylene, carbon monoxide and ethylene with their concentration increasing respectively by 195%, 126%, 103% and 82%, while alcohol increased 35%, but the aldehydes reduced 7%. Simulation results showed that the intermediate products in residual gas advanced auto-ignition timing 2°CA, while with fuel reforming, 0.5 more°CA advancing can be achieved.The effects of the fuel ratio injected during NVO on HCCI combustion are exhibited nearly the same under different air-fuel ratio situation. The increase of fuel ratio injected during NVO reduced the requirements of temperature and pressure to achieve auto-ignition which leads to the advancing of the auto-ignition timing. As a result of advanced auto-ignition, the combustion duration became shorter, while the maximum cylinder pressure and maximum pressure rise rate increased.