Studies on Improvement of Combustion with an Accumulator-type Fuel Infection System Coupled with Pilot Injection

已经进行了研究，以检查高压燃油喷射和先导喷射对改善燃烧的影响，这意味着在不增加NO排放的情况下减少柴油机的BSFC和排气烟雾密度。不仅通过安装新研制的蓄能器式燃油喷射系统的试验发动机的运行试验，而且通过对另一台具有可视化燃烧室的试验发动机的燃油喷射和火焰的高速照片的分析，阐明了这些效果。实验结果表明：(1)使用与高喷射压力相对应的孔径较小的喷油嘴对改善燃烧特性是有效的，因为燃油喷射的过剩空气比增加了。(2)先导/预喷后再进行高压喷射，在不增加NO排放的情况下，有效降低了BSFC和排气烟密度。(3)与船用柴油相比，残余燃油喷雾更难被空气旋流分散，需要较高的旋流强度才能达到最佳燃烧。(4)燃油喷雾与活塞壁面碰撞燃烧和空气涡流燃烧是改善扩散燃烧期残余燃油喷雾燃烧的有效手段，其燃烧方式是将气体部分和液芯中的小液滴吸走，并向喷雾提供新鲜燃油。(5)燃烧室内燃烧空气温度的升高，通过加速馏分组分的蒸发，改善了残余燃油喷雾的燃烧。(6)应注意的是，在低压缩空气温度下，残余燃料的放热率随着点火延迟时间的增加而急剧下降。

Studies have been carried out to examine both the effects of high pressure fuel injection and pilot injection on the improvement of Combustion, that means reductions of BSFC and exhaust smoke density without increase in NO emission, in a Diesel Engine. The effects were clarified not only by operation tests with the test engine equipped with a newly developed accumulator-type fuel injection system, but also from analyses of high sped photographs of fuel spray and flames taken in another test engine with a visualized combustion chamber. As the results of experiment following Conclusions have been obtained.(1) It is effective on the improvement of combustion characteristics to use the injection nozzle with smaller hole diameter corresponding to the high injection pressure, because of the increase in the excess air ratio of fuel spray.(2) The pilot/pre injection followed by high pressure injection is effective on reductions of BSFC and exhaust smoke density without increase of NO emission.(3) Residual fuel spray is more difficult to be dispersed by air swirl and needs high swirl intensity for the optimum combustion than marine diesel oil.(4) Combustion of impingement of fuel spray on the piston wall and air swirl is an effective means to improve the combustion of residual fuel spray in the diffusion combustion period by talking off the gaseous part and small droplets from the liquid core and supplying the spray with fresh oil.(5) Increase of combustion air temperature in the combustion chamber improves the combustion of residual fuel spray by accelerating the evaporation of distillate components.(6) Attention should be paid to the fact that the heat release rate of residual fuels goes down extremely with the increase of ignition delay at low compression air temperature.