A Low-NOx High-Efficiency Engine System for Alternative Fuels by Mean of Ultra-Lean Homogeneous-Charge Premixed Combustion

本研究旨在建立一种高效率低氮氧化物发动机的替代燃料在稀薄燃烧。本文的主要研究内容如下：1.在一台燃用天然气和液化石油气的火花点火式发动机上，研究了均质预混合气的稀燃极限，给出了确定该极限的因素和扩展该极限的方法。2.在不同型号和尺寸的发动机上进行的稀燃试验表明，均质预混合气比非均质预混合气能更好地降低NOx排放浓度。此外，温度和NO浓度的历史计算使用的热力学模型的基础上测得的混合物具有不同程度的异质性的热释放速率。结果表明，具有更均匀混合物的稀燃发动机是理想的，并且一旦在燃烧期间人为地混合燃烧气体， ...更多信息 3.采用傅里叶变换红外光谱仪对稀燃发动机的排放进行了实时测量。从测量结果可知，在稀薄燃烧中，不仅未燃HC增加，而且燃烧生成的HC也增加。此外，还测量了冷启动条件下的尾气排放特性，在点火操作后检测到高浓度的HCs，而NOx从开始就逐渐增加。4.基于火焰发展子模型，建立了均质充气发动机燃烧过程和NO生成的三维模型。对不同工况进行的计算，较好地再现了整个燃烧过程。的热释放速率，火焰温度和NO浓度的空间分布进行了研究，以澄清NO的形成机制，特别注意在燃烧过程中的热量和质量的混合。少

This study aims at the establishment of the high-efficiency low-NOx engine for alternative fuels at lean homogeneous-charge combustion. The contents of the present study are summarized as follows :1.Lean limits of homogeneous premixture were investigated in a spark-ignition engine fueled by naturalgas and LPG,and the factors for determining the limit and the method for extending it were shown.2.Experiments for a variety of engine types and sizes at lean-burning operations show that a homogeneous mixture allows much more reduction of the exhaust NOx concentration than a heterogeneous mixture. In addition, the histories of temperature and NO concentration were calculated using a thermodynamic model based on the measured rates of heat release for the mixture having different degrees of heterogeneity. It was shown that a lean-burn engine with a more homogeneous mixture is desirable, and that much reduction of NO may be achieved once the burnt gas is artificially mixed during combustion to … More make the burnt zone more uniform.3.Real-time measurement of exhaust gas emissions in a lean-burn gas engine was carried out by using Fourier transform infrared spectroscopy analyzer. From the measured results, it was shown that not only unburnt HC but also combustion-generated HC increase in lean combustion. Furthermore, the characteristics of exhaust emissions under a cold start condition were measured, and high concentrations of HCs were detected just after the firing operation, whereas NOx gradually increases from the start.4.A three-dimensional model for the combustion process and NO formation in a homogeneous-charge engine was established based on a submodel for flame development. Computations carried out for different conditions gave a good reproduction of the entire combustion process. The spatial profiles of heat-release rates, the flame temperature and the NO concentration were investigated to clarify the mechanism of NO formation with special attention to mixing of heat and mass in the combustion process. Less