EGR率对乙醇/生物柴油混合燃料燃烧及排放特性的影响

Effects of EGR Rate on Combustion and Emission Characteristics of Blends of Ethanol and Biodiesel

在一台经过深度改装的四缸直喷水冷柴油机上,燃用乙醇与生物柴油的混合燃料,研究了EGR率与燃料特性对柴油机燃烧及排放的影响.结果表明:EGR系统的介入以及乙醇的掺混均可减小燃烧过程中缸内压力和放热率峰值.燃用同种掺混比的燃料,随着EGR率的增大,滞燃期和燃烧持续期出现了不同程度的延长,当量燃油消耗率升高,有效热效率降低.EGR率不变时,燃用不同掺混比的混合燃料,随乙醇质量分数的增加,滞燃期与燃烧持续期逐渐延长,当量燃油消耗率逐渐降低,有效热效率逐渐升高.NO_x的排放量在EGR引入后出现了显著下降,HC排放量升高.相同EGR率下,随着乙醇掺混比的提高NO_x排放量略微下降,HC排放量表现出先减小后升高的趋势.相比纯生物柴油,乙醇的掺混可以显著减少大粒径颗粒物的数量.EGR率的变化对核模态粒子的数量影响不明显,但聚集态粒子的数量会随着EGR率的提高出现较为明显的增多.将乙醇、生物柴油和EGR系统三者相耦合可改善柴油机的燃烧及排放特性.

Experiments were carried out on a deeply modified four-cylinder DICI engine,and the blends of ethanol and biodiesel were used to study the effects of exhaust gas re-circulation(EGR)rate and fuel characteristics on the combustion and emissions of diesel engine.Results show that both the intervention of EGR system and ethanol blending could reduce the peak cylinder pressure and heat release rate during combustion.With fuels at the same blending ratio and the increase in the EGR rate,the ignition delay and combustion duration were prolonged to varying degrees;the equivalent fuel consumption rate increased,whereas the effective thermal efficiency decreased.When the EGR rate was constant,the mixed fuel at different blending ratios was used. As the mass fraction of ethanol increased,the ignition delay and combustion duration were gradually prolonged,the consumption rate of equivalent fuel decreased,and the effective thermal efficiency increased.After the introduction of EGR,NO_x emissions dropped significantly,whereas HC emissions increased.At the same EGR rate,the NO_x emissions decreased slightly with the increase in the ethanol blending ratio,and the HC emissions initially decreased and then increased.Compared with pure biodiesel,ethanol blending could significantly reduce the number of large size particles.The effects of changes in EGR rate on the number of nucleation mode particles were not obvious,but the number of aggregated particles increased significantly with the growing EGR rate.The coupling of ethanol,biodiesel and EGR system could improve the combustion and emission characteristics of diesel engine.