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在性能、燃料消耗和排放方面对大型天然气发动机提出了更高的要求。未来的排放限制将需要开发新的、在不降低发动机效率和功率的前提下显著降低排放的技术。达到此目的的一条途径就是使用催化剂(氧化催化剂、SCR催化剂)。这种方法的缺点是催化剂和为了减少氮化物的排放而使用的添加剂的成本较高。另一途径是采用新的燃烧技术达到减少排放的目的,例如均质充量压燃(HCCI)技术。本文将介绍采用天然气达到均质自燃目的的各种方法。采用非常高的压缩比、高废气再循环率以及很高的进气管温度,实现了纯天然气的HCCI技术。此外,亦研究了双燃料系统。采用了柴油作为第二种燃料用于内部混合以及采用了正庚烷、汽油、柴油用于外部混合等方式。所有的实验均是在一台排量约为6·2L的单缸试验机上进行的。研究结果显示出在采用HCCI技术的条件下不同参数(压缩比、进气管温度、废气再循环率)对燃烧过程的影响,以及发动机所能达到的效率和对排放性能的影响。
Higher demands are placed on large natural gas engines in terms of performance, fuel consumption and emissions. Future emission limits will require the development of new technologies to reduce emissions significantly without reducing engine efficiency and power. One way to do this is to use a catalyst (oxidation catalyst, SCR catalyst). The disadvantage of this method is that the cost of the catalyst and additives used to reduce the emission of nitrides is high. Another approach is to adopt new combustion technologies for emission reduction purposes, such as homogeneous charge compression ignition (HCCI) technology. This article describes various ways to achieve the goal of homogeneous spontaneous combustion with natural gas. HCCI technology for pure natural gas is achieved with a very high compression ratio, high exhaust gas recirculation rate and high intake pipe temperature. In addition, dual fuel systems have also been studied. Diesel is used as the second fuel for internal mixing and for n-heptane, gasoline and diesel for external mixing. All experiments were performed on a single cylinder test machine with a displacement of about 6.2L. The results show the influence of different parameters (compression ratio, intake manifold temperature, exhaust gas recirculation rate) on the combustion process with HCCI technology and the engine’s achievable efficiency and emission performance.