摘要
国六天然气发动机采用等当量燃烧结合外部冷却EGR及TWC的排放控制技术路线，TWC的转化效率是保证发动机排放达标的重要因素，而催化器的入口温度是决定TWC转化效率高低的最重要影响参数之一。然而，在冷起动阶段及排气管路温降较大的情况下，存在TWC入口尾气温度难以满足发动机及整车排放高效转化需求的问题。针对该问题，在一台4.5 L排量的发动机和一辆搭载该发动机的城市环卫车上探究不同尾气热管理策略对发动机WHTC循环排放及整车作业循环排放的影响。研究结果表明：采用起动快速温升的尾气热管理策略，能有效提高冷起动阶段发动机尾气温度，WHTC循环的TWC入口温度达到300 ℃所需时间缩短了300 s，显著降低了NOx，CH4和CO循环排放，降幅分别达到38.5%，38.5%和5.8%；采取在TWC上增加金属载体前级方案的尾气控制策略，WHTC循环的NOx，CH4和CO循环排放分别降低了62.2%，42.8%和15.7%；采用对整车排气尾管包裹的尾气热管理策略，在整车作业循环工况下，TWC入口温度相比采用普通石棉包裹的方案提高了近200 ℃，使得NOx瞬时排放值30 s平均值的最大值降低了60.9%，能更好地满足北京第六阶段的排放法规要求。
Abstract
The China Ⅵ natural gas engine adopts the emission control technology route of equivalent combustion combined with external cooling EGR and TWC. The conversion efficiency of TWC is an important factor to ensure that the engine emissions meet the standards, and the inlet temperature of the catalytic converter is one of the most important influencing parameters that determine the conversion efficiency of TWC. However, there is a problem that the inlet exhaust gas temperature of TWC is difficult to meet the high-efficiency conversion requirements of engine and whole vehicle emissions in the cold start stage and under the condition of large temperature drop of exhaust pipe. To address this issue, different exhaust thermal management strategies were investigated on a 4.5 L displacement engine and an urban sanitation vehicle equipped with the engine to study the effects on engine WHTC cycle emissions and whole vehicle operation cycle emissions. The results showed that the exhaust thermal management strategy with rapid temperature rise could effectively increase the exhaust gas temperature of engine during cold start. The time required for the TWC inlet temperature to reach 300 ℃ during WHTC cycle was shortened by 300 s, which significantly reduced NOx, CH4, and CO cycle emissions with the reductions of 38.5%, 38.5% and 5.8% respectively. The exhaust control strategy that added a metal carrier upstream of TWC produced the reductions of 62.2%, 42.8% and 15.7% respectively in NOx, CH4, and CO cycle emissions during WHTC cycle. Compared with the scheme using ordinary asbestos wrapping, the inlet temperature of TWC increased by nearly 200 ℃ under the whole vehicle operation cycle after using the exhaust thermal management strategy with a special wrapping process for the entire vehicle exhaust pipe, which resulted in a maximum reduction of 60.9% in the 30 s average value of transient NOx emissions. Accordingly, the emission regulation requirements of Beijing＇s Ⅵ stage can be better met.
关键词
天然气发动机 /
当量燃烧 /
尾气热管理 /
冷起动 /
排气温度
Key words
NG engine /
equivalent combustion /
exhaust thermal management /
cold start /
exhaust temperature
邓远海，宁德忠，蒋继，潘恒斌，付长城，官维.
不同尾气热管理策略对当量天然气发动机WHTC循环排放的影响[J]. 车用发动机. 2024, 0(2): 53 https://doi.org/10.3969/j.issn.1001-2222.2024.02.008
DENG Yuanhai，NING Dezhong，JIANG Ji，PAN Hengbin，FU Changcheng，GUAN Wei.
Effects of Different Exhaust Thermal Management Strategies on WHTC Emission for Equivalent NG Engine[J]. Vehicle Engine. 2024, 0(2): 53 https://doi.org/10.3969/j.issn.1001-2222.2024.02.008
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