Influence of emulsified fuel combustion on soot formation process

柴油机碳烟和氮氧化物（NOx）的排放存在一种折衷关系，难以同时实现。水的添加是有效的，以减少氮氧化物的排放量，而不恶化的燃烧性能。然而，目前还不清楚水的添加如何影响烟尘和颗粒物的排放。首先，在实际柴油机上进行了燃用油包水型乳化燃料的烟度形成特性试验。研究了柴油和生物柴油两种基础燃料、废气再循环（EGR）和水添加量对柴油机燃烧性能的影响。与无水燃料相比，乳化燃料在所有操作条件下的烟密度均显着降低。为了研究颗粒的形成过程，采用模型室进行了实验。模拟柴油机燃烧是可能的，采用了模拟定容燃烧的模型室。实验装置由五个部分组成：柴油发动机的改进燃烧室，高温高压空气容器，带有由螺线管驱动的针切割器的破裂系统，容纳膨胀气体的容器，以及用于单次喷射柴油燃料的系统。薄钢板用于分隔燃烧室和气体膨胀容器。在燃烧过程中，薄板被针切割器破裂，燃烧反应立即停止，因为燃烧气体在极短的时间内膨胀。初步燃烧实验在大气条件下进行，初始空气压力为2MPa，温度为450℃，点火延迟期比实际发动机长。该仪器需要改进以获得更精确的数据。

It is difficult to achieve simultaneous reductions in soot and nitrogen oxides (Nox) emitted from diesel engines because of the trade-off relation. Water addition is effective to reduce Nox emissions without deterioration in the combustion performance. It is unclear, however, how the water addition influences the soot and particulate emissions. First, experiments were carried out to determine the formation characteristics of smoke emissions using actual diesel engines fueled with water-in-oil emulsified fuels. The experimental parameters with two types of base fuel (gas oil and biodiesel, fuel transesterified from vegetable oil), EGR (exhaust gas recirculation), and water addition were investigated. Compared with water free fuels, the smoke density of the emulsified fuels reduced remarkably at all operating conditions.To examine the formation process of particulate, experiments using a model chamber were made. It is possible to simulate diesel combustion and a model chamber simulating constant volume combustion was employed. The experimental apparatus consisted of five parts : a modified combustion chamber of the diesel engine, a vessel for high temperature and high pressure air, a rupture system with a needle cutter driven by a solenoid, a vessel to contain expanded gas, and a system for single injections of diesel fuel. A thin steel plate is used to partition the combustion chamber and the gas expansion vessel. In the combustion process the thin plate is ruptured by the needle cutter and the combustion reaction stops immediately, because the burnt gas expands in an extremely short time. The preliminary combustion experiments were conducted at atmospheric conditions with an initial air pressure of 2MPa and 450℃, and the ignition delay was longer than with actual engines. The apparatus will need improvements to obtain more precise data.