Development of a Premixture Combustion Type Diesel Engine Using a Microhole Injection Nozzle

本研究的目的是减少柴油发动机的烟尘和氮氧化物排放，保持高热效率。为此，我们提出了一种新的柴油机燃烧概念，它比传统的柴油机燃烧更均匀地燃烧预混料。这一概念将通过多个微孔喷嘴的组合来实现，该喷嘴的孔径是传统喷嘴的十分之一，并带有高压燃油喷射系统。本研究取得了以下结果：(1)利用激光打孔成功制作了孔径为0.06 mm的多微孔喷嘴。(2)采用膛径为60mm的燃烧室快速压缩膨胀机，研究了孔径大小对点火延迟和燃烧的影响。测量结果表明，在2.8MPa-8.5MPa的环境压力范围内，将孔直径从0.15 mm减小到0.06 mm可使点火延迟时间缩短30%。采用微孔喷管对直喷式发动机的燃烧性能进行了测试，结果表明，微孔喷管的点火延迟时间缩短，烟雾排放减少，但NOx排放没有减少。(3)研制了一种采用阀芯加速和油锤的高压柴油喷射系统，并对该喷油器的性能进行了研究。结果表明，通过改变阀芯预升程和阀芯双加速度，可以控制初始喷射速率，实现先导喷射。该喷射系统可用于研究喷射速率对微孔喷嘴喷射火焰中混合物形成的影响。

The objective of this study is to reduce the soot and NOx emissions from diesel engines keeping the thermal efficiency high. For this purpose, we proposed a new combustion concept of diesel engines, which burns premixture like more uniform mixtures than that of conventional diesel combustion. This concept will be achieved by a combination of a multiple micro-hole nozzle, having an orifice diameter of one tenth of that of the conventional nozzle, with high-pressure fuel injection system. In this study, the following results were obtained :(1) We succeeded to make the multiple micro-hole nozzle with an orifice diameter of 0.06 mm by a laser drilling.(2) The effects of orifice size on ignition delay and combustion were investigated using a rapid compression and expansion machine which has a combustion chamber with a bore size of 60 mm. The measurement results showed that decreasing orifice diameter from 0.15 mm to 0.06 mm shortens the ignition delay by 30% in a wide range of ambient pressure of 2.8MPa-8.5MPa. The measurement of combustion behavior with a micro-hole nozzle in a DI engine was also carried out and the results revealed that the ignition delay is shortened and smoke emission is reduced, but NOx emission is not reduced.(3) A high-pressure diesel fuel injection system using spool acceleration and oil hammering was developed, and the performance of this injector was investigated. The results demonstrated that it is possible to control the initial injection rate and achieve the pilot-injection by changing the pre-lift of spool and double-acceleration of spool. This injection system was found useful for the study of the effect of injection rate on the formation of mixture in a spray flame with a micro-hole nozzle.