The contribution of EGR on the fuel consumption improvement is analyzed based on both test and simulation.A 1.3 T gasoline engine is modified with EGR system for the test.With the introduction of EGR,parameters such as throttle opening angle,ignition timing and intake VVT are optimized,leading to a decrease of 2.4％,4.7％ and 13.2％ in fuel consumption at low load,middle load and high load,respectively.With one-dimensional simulation,heat transfer loss,constant volume ratio and mechanical loss are analyzed.The results show that under low load,the optimization benefits of EGR come from the decrease of heat transfer loss.Under middle load,the EGR benefit comes from the decrease of heat transfer loss plus the increase of constant volume ratio.Under high load,the benefit comes from the increase of constant volume ratio.As for the evaluation of constant volume ratio,a thermodynamics engine cycle model is designed to quantify and compare the constant volume ratio.It appears that under low load the constant volume ratio is slightly decreased due to EGR,but it is increased under middle and high loads.In detail,the increase at high load is 16.0％,much higher than that of 2.4％ under middle load.%基于一台1.3 T小型涡轮增压汽油机,采用低压废气再循环(EGR),通过调整节气门开度、点火正时以及进气可变气门正时(VVT)对燃油消耗率进行优化,在小、中和大3种负荷分别得到了2.4％、4.7％和13.2％的燃油消耗率改善.结合一维仿真,分析了引入EGR后不同因素对燃油经济性改善的贡献程度,得到结论:在小负荷对节油率的贡献主要来自于传热损失的降低,中负荷来自传热损失的降低和等容度的提高,而大负荷则是由于等容度的提高.针对等容度评价,提出了一种理论模型将其量化比较,发现受到燃烧持续期以及燃烧重心的共同影响,小负荷时EGR优化燃油消耗率后会略微降低原机在该工况下的等容度,中负荷和大负荷则有不同程度的提升,大负荷的提升程度为16.0％,明显大于中负荷时的2.4％.
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