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

本研究旨在建立稀薄均质充量燃烧替代燃料的高效低NOx发动机。本文的研究内容概括如下：1.研究了燃用天然气和液化石油气的火花点火式发动机均质预混合气的稀薄极限，给出了确定稀薄极限的因素和扩大稀薄极限的方法。2.在不同类型和尺寸的发动机上进行的稀薄燃烧试验表明，均质混合气比非均质混合气可以更好地降低NOx排放浓度。此外，根据测量的不同非均质程度混合气的放热速率，利用热力学模型计算了温度和NO浓度的历史。结果表明，稀燃发动机具有更均匀的混合气是可取的，一旦在燃烧过程中将燃烧的气体人工混合到…中，可以大大降低NO的排放量利用傅里叶变换红外光谱仪对稀燃内燃机的尾气排放进行了实时测量。从测量结果可以看出，稀薄燃烧不仅有未燃HC的增加，而且燃烧产生的HC也有增加。此外，还测量了冷启动条件下的排放特性，并在点火后即刻检测到高浓度的HCS，而NOx从启动后逐渐增加。4.在火焰发展子模型的基础上，建立了均质充气发动机燃烧过程和NO生成的三维模型。在不同条件下进行的计算很好地再现了整个燃烧过程。研究了燃烧过程中放热速率、火焰温度和NO浓度的空间分布，重点研究了燃烧过程中热量和质量的混合，以阐明NO的生成机理。较少

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