点燃式重型天然气发动机燃烧技术的发展及其应用  

The development and application of combustion technologies for spark ignition heavy-duty natural gas engines

作　　者：尧命发[1] 闫博文[1] 郑尊清[1] 覃玉峰[2] 

机构地区：[1]天津大学内燃机燃烧学国家重点实验室 [2]广西玉柴机器股份有限公司

出　　处：《天然气工业》2017年第10期79-86,共8页Natural Gas Industry

基　　金：国家自然科学基金项目"基于混合气分层与燃料化学活性控制的内燃机燃烧理论研究"(编号:51320105008)

摘　　要：稀燃与当量燃烧是点燃式重型天然气发动机的两种主要燃烧方式。其中,稀燃技术凭借高效清洁燃烧的优势长期占据主导地位,然而随着欧Ⅵ法规的逐渐推行,稀燃发动机必须加装选择性催化还原(Selective Catalytic Reduction,SCR)装置才能满足氮氧化物的排放要求。相比之下,当量燃烧结合三效催化器可实现超低排放量并明显降低后处理成本,正受到越来越多的关注。为此,阐述了上述两种燃烧方式各自的优势及面临的问题,进而提出了相应的优化技术措施。结论认为:(1)稀燃发动机可通过拓展稀燃极限,在不加装NO_x后处理装置的情况下满足欧Ⅴ排放法规要求,同时实现较高的热效率,但要进一步满足欧Ⅵ法规则必须加装SCR;(2)相比燃烧室及进气道结构的优化,采用局部分层或预燃室结构更有利于拓展稀燃极限并实现稳定燃烧,在相同NO_x排放量水平下可以明显改善热效率,但过稀混合气区域的增加将导致未燃碳氢的排放量明显上升;(3)采用稀燃方式结合SCR满足欧Ⅵ排放法规时,还可采用少量废气再循环稀释进一步抑制原始NO_x排放量,以获得更好的燃烧相位;(4)针对当量燃烧结合少量废气再循环的方式,采用米勒循环可有效提高热效率,但是,随着气门关闭时刻推迟或提前,即使有效压缩比保持不变或有所增加,燃烧速率仍降低,若气门关闭时刻推迟或提前较少,有效压缩比将提高,会导致传热损失及大负荷爆震倾向明显增加。Lean burn and stoichiometric are two main combustion modes in spark ignition heavy-duty natural gas engines. And due to its efficient and clean combustion, the lean-burn technology has been playing a dominant role for a long time. As EU-V legislation is im- plemented gradually, however, a lean-burn engine cannot satisfy the nitrogen oxides （NO~） emission requirements unless it is equipped ~vith a selective catalytic reduction （SCR） unit. On the contrary, stoichiometric combustion has been given more and more attention, for altra-low emission and obvious low post-treatment cost can be realized when it is combined with a three-way catalyst. In this paper, the advantages and problems of both combustion modes were illustrated and optimization measures were proposed correspondingly. Based on ：he analysis, the following conclusions were reached. First, a lean-burn engine can satisfy the EU-V emission legislation if its combustion imit is extended with no installment of any NO, post-treatment unit, and a higher thermal efficiency can be realized. In order to satisfy EU-VI legislation, however, it has to be equipped with SCR. Second, compared with the optimization of combustion chambers and intake borts, both regional stratification and pre-combustion chambers are more favorable for lean-burn limit extension and stable combustion. ~.nd in the same level of NOx emission, they can increase the thermal efficiency significantly, but much more unburned hydrocarbon will be emitted if the mixed gas zone is too thin. Third, if lean burn is combined with SCR to satisfy EU-VI emission legislation, the original Nox emission can be inhibited further by recirculation and dilution of a little burned gas, so that the combustion phase will get better. And burth, if stoichiometric combustion is combined with the recirculation of a little burned gas, the thermal efficiency can be increased effectively by means of Miller cycle. If the air valve is not closed on time, however, the combustion rate will still drop even though the ef

关 键 词：点燃式天然气发动机 稀燃 当量燃烧 热效率 排放法规 SCR 三效催化器 优化措施 

分 类 号：TK401[动力工程及工程热物理—动力机械及工程]