Low NOx stratified combustion of a compressed natural gas with an over-expansion injector

本研究旨在揭示利用超音速气流的过膨胀特性的可行性。它将在燃料射流处产生比环境空气更低的压力区域，环境空气预期被吸入燃料射流中，并且燃料射流的中心区域中的更富区域将变得更贫，从而导致更低的燃烧温度和更低的NOx形成。在此基础上，通过对压比和马赫数平面上的这种行为的估计，预测了在快速压缩机实现的高温高压环境下的激波形态。当在快速压缩机中应用5.8的减小的压缩比时，观察到燃烧效率的轻微增加和CO的减少，这表明形成过膨胀条件的效果。然而，检测到的NOx水平的变化很小。因此，在较低的压缩比下实现了过膨胀效应， ...更多信息 为了在亚音速条件下将环境空气引入燃料射流中，还测试了利用湍流混合的空气卷吸，即所谓的本生燃烧器机制。在大气压条件下进行稳态实验台实验，成功观察到了进气现象。然而，在快速压缩机的实验中，这种空气引入的效果很小。因此，它也表明，空气的引入是不够有效，以减少NOx的排放。在应用到发动机燃烧，喷油器的定位效果进行了检查，因为它通常是有限的气缸盖。进行了喷油器位置、侧喷和中心喷的对比研究。中心喷射在高当量比工况下燃烧效率有所提高，但在稀油工况下燃烧效率下降明显。这是由于燃料射流和燃烧室壁之间的相互作用而使中心喷射更好地混合而产生的。从而明确了喷油器定位的重要性，并提出了未来喷油参数确定策略的必要性。少

The present study aimed at revealing the feasibility of utilizing over-expansion behavior of supersonic gas flow. It would generate lower pressure area at the fuel jet than the ambient air, the ambient air was expected to be sucked into the fuel jet, and the richer zone in the central region of the fuel jet would become leaner resulting in lower combustion temperature and lower NOx formation. On the basis of the estimation of this behavior on the pressure ratio and the mach number plane, the shock wave pattern was predicted under the condition of high pressure and temperature ambient realized by a rapid compression machine. When the reduced compression ratio of 5.8 in the rapid compression machine was applied, slight increase of combustion efficiency and reduction of CO were observed, which suggested the effect of formation of over-expansion condition. However, little variation of NOx level was detected. Thus the over-expansion effect was realized at lower compression ratio and the ext … More ent is not so remarkable.For introducing ambient air into the fuel jet at subsonic condition, utilization of air entrainment with turbulent mixing, so-called Bunsen burner mechanism, was also tested. Under atmospheric condition with steady-state test rig experiment, the phenomenon of air introduction was successfully observed. However, in the experiment of rapid compression machine, little effect of such air introduction was obtained. Thus it was also shown that the air introduction is not so effective enough to reduce NOx emission.In terms of application to engine combustion, effect of injector positioning was examined since it is normally limited to cylinder head. Comparison study of injector positioning, side and central injection was carried out. With the central injection, combustion efficiency was increased at higher equivalence ratio condition but it deteriorated much at leaner condition. This would be generated by the better mixing of central injection due to the interaction between the fuel jet and the combustion chamber wall. Thus the importance of fuel injector positioning was clearly shown and the need of the future strategy of injection parameter determination was suggested. Less