Thermodynamic analysis of EGR effects on the first and second law efficiencies of a boosted spark-ignited direct-injection gasoline engine
Thermodynamic analysis of EGR effects on the first and second law efficiencies of a boosted spark-ignited direct-injection gasoline engine
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DOI：
10.1016/j.enconman.2013.03.001
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发表时间：
2013-06
影响因子：
10.4
通讯作者：
Tie Li;Dawei Wu;Min Xu
中科院分区：
文献类型：
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作者：
Tie Li;Dawei Wu;Min Xu
废气再循环（EGR）是提高汽油机燃油经济性的有效手段，但其具体机理还有待进一步研究。本文基于热力学第一、第二定律，通过发动机试验和一维循环模拟，深入分析了冷却EGR对增压、火花点火、直喷汽油机在全负荷、中负荷和低负荷工况下燃油转化效率的影响。对于所有的运行负载，EGR增加了工作气体的比热比，减少了通过燃烧室壁的热传递的分数，并改善了在气体交换冲程期间的泵送功。此外，EGR还可以替代高负荷时的燃油增浓，提前燃烧相位，提高中高负荷时的定容放热程度。结果表明，在不同负荷下，12- 17%EGR可使制动器热效率提高1.1-4.1%。尽管燃烧产生的不可逆性（可用性或火用的破坏）的分数增加，总可用性中的指示功的分数随着所有操作负载的EGR而增加。在这些影响因素中，在空燃比恒定的情况下，由于EGR而减少传热损失的效果在提高燃料转换效率方面占主导地位，而用EGR代替燃料富集在满负荷时最有效。
Exhaust gas recirculation (EGR) is effective to improve fuel economy of spark-ignition gasoline engines, but the detailed mechanism needs to be further investigated. In this paper, an in-depth analysis of the effects of cooled EGR on the fuel conversion efficiency of a boosted, spark-ignited, direct-injection, gasoline engines operated at the full, medium and low loads is conducted with the engine experiment and 1-D cycle simulation based on the first and second laws of thermodynamics. For all the operating loads, EGR increases the ratio of specific heat of working gas, reduces the fraction of heat transfer through the combustion chamber walls, and improves the pumping work during the gas exchanging stroke. Besides, EGR may replace the fuel enrichment at high load, advance the combustion phasing and increase the degree of constant volume heat release at the medium and high loads. As a result, about 1.1–4.1% improvements in the brake thermal efficiency are obtained by the 12–17% EGR at different loads. Despite the increased fraction of combustion-generated irreversibility (destruction in availability or exergy), the fraction of indicated work in the total availability increases with EGR for all the operating loads. Among the influencing factors, the effect of reduction in the heat transfer loss owing to EGR is dominant in improvement of the fuel conversion efficiency at constant air–fuel ratio, while replacement of the fuel enrichment with EGR is most effective at full load.