Experimental Investigation Of Combustion Cyclic Variations In Un-throttled Gasoline Engine

The continuous variability of maximum valve lift,opening duration and valve timing can be attained by fully hydraulic variable valve system(FHVVS).BJ486EQ un-throttled gasoline engine was developed by using self-developed FHVVS.The intake performance and combustion performance studies were carried on FHVVS prototype.Based on the comparison with the experimental results of throttle gasoline engine,the phenomenon of combustion cyclic variations on the un-throttled gasoline engine is analyzed and studied,and a variety of measures were proposed to improve the combustion cyclic variations on un-throttled gasoline engine.The main research contents are as follows:Firstly,un-throttled gasoline engine prototype was developed and test bench was built.The BJ486EQ gasoline engine is equipped with FHVVS institution,to achieve the throttle-free control of load.The gasoline engine test bench was built,and meanwhile,the corresponding test equipment and experimental test system were improved.Secondly,The influence of FHVVS on combustion performance of un-throttled gasoline engine was investigated.The combustion cycle of un-throttled gasoline engine is analyzed by measuring its in-cylinder pressure.The results show that the amount of residual exhaust in the cylinder of the un-throttled gasoline engine is very small compared with the throttle gasoline engine at the low load,which is not conducive to the evaporation and mixing of the fuel,resulting in the unstable combustion performance and the significant increase of the combustion cyclic variations.In addition,since the un-throttled gasoline engine eliminates the throttle,the temperature and pressure at the end of compression are reduced,and the ignition stability is deteriorated,resulting in an increase of combustion cyclic variations.Thirdly,a variety of measures were proposed to improve the combustion cyclic variations un-throttled gasoline engine.By changing the ignition advancing angle,changing the intake temperature,enhancing the ignition energy and the intake swirl to explore the change rule of the cyclic variations on the un-throttled gasoline engine.The results show that the increase of the ignition advancing angle can improve the combustion performance,so that the center of heat release(CA50)can be adjusted to the recommend position,but some misfire cycles are unfortunately occurred when ignition advance angle is too large,which leads to the significant increase of combustion cyclic.The improving intake temperature has certain effect on the improvement of the combustion cyclic variations,but the effect is not obvious.The enhanced ignition energy can also make cyclic variations improved,but it has some limitations that cyclic variations still be increased on the low load and larger ignition advancing angle condition.Fourthly,the team developed a new helical intake valve that can produce strong intake swirl,which can promote the fuel evaporation and mix,significantly decrease the cyclic variations of un-throttled gasoline engine at part load operating condition and improve the indicated heat efficiency.The results show that when the brake mean effective pressure is 0.19MPa,in compare to original intake valve,the using of helical intake valve makes the rate of cyclic variations decreased from 44.3%to 2.7%.