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一、前言直喷式柴油机具有较高的热效率,因此,不但在中低速柴油机、甚至在总排气量小于10公升的中高速柴油机中也已经得到了广泛的应用。但是,在直喷式柴油机中,对氮氧化物(NOx)和排烟采取净化措施后,一般情况下燃油消耗率有所增加,而当前尚未找到恰当的排气净化方法。近来,看到了锅炉中使用乳化燃油(水混入燃油的油中水滴形乳化燃油。以下简称为油包水形乳化燃油——译注),在降低燃油消耗率及NOx的浓度方面取得成功的一些例子。同时也有报告指出,在柴油机上使用这种油包水形乳化燃油后,同样成功地降低了燃油消耗、烟度或NOx的浓度。本文首先根据气缸内火焰的高速照片和高温空气流管道内的燃烧照片,查明了在直喷式柴油机上使用一般燃油和乳化燃油(采用1%的界面活性剂制成的油包水形乳化燃油)时燃烧过程的差异。结果表明,随燃油种类的不同,发火开始状态和燃烧过程存在着差异。为此,对活塞顶的形状和燃油喷雾在燃烧室内的分散状态等作了多种改变,以探讨适合于使用乳化燃油的燃烧室形状。另外,也在实际使用的高速直喷式柴油机上使用这种乳化燃油,并研究使用时产生的问题及其相应的解决措施。
I. INTRODUCTION The direct injection diesel engine has high thermal efficiency. Therefore, it has been widely used not only in medium and low speed diesel engines, but also in medium and high speed diesel engines with a total displacement of less than 10 liters. However, in direct-injection diesel engines, the purification rate of nitrogen oxides (NOx) and exhaust fumes has generally increased the fuel consumption rate, and no proper exhaust gas purification method has been found yet. Recently, we have seen some examples of success in reducing the fuel consumption and the NOx concentration in the boiler by using emulsified fuel (water-in-oil emulsion oil, hereinafter abbreviated as water-in-oil emulsified oil) . It has also been reported that the use of such water-in-oil emulsions on diesel engines has also succeeded in reducing fuel consumption, smoke or NOx concentrations. Based on the high-speed photos of the flame in the cylinder and the combustion photographs in the high-temperature air flow pipe, it was found that the common fuel and emulsified fuel (1% surfactant-based water-in-oil emulsified Fuel) combustion process differences. The results show that there is a difference between the initial state of ignition and the combustion process depending on the type of fuel. For this reason, many changes have been made to the shape of the piston top and the dispersion state of the fuel spray in the combustion chamber, etc. to investigate the shape of the combustion chamber suitable for the use of emulsified fuel. In addition, this kind of emulsified fuel is also used on the actual high-speed direct-injection diesel engine, and the problems arising in use and the corresponding solutions are also studied.