基于一维／三维模型耦合的富氧燃烧天然气发动机数值模拟

摘要

以某1．0 L3缸汽油机为基础，利用 GT-Power与Converge建立了天然气发动机耦合仿真模型，并利用原机试验数据对模型进行了验证，研究了进气富氧与 EGR 对天然气发动机性能的影响特性，对利用进气富氧与EGR 改善天然气发动机的性能进行了探讨。结果表明，随进气氧气体积分数提高，天然气发动机平均有效压力显著提高，最大可提高22．8％（氧体积分数为28％时）；同时缸内温度和 NOx 排放升高，排气与传热的能量损失增加，燃气消耗率略有升高。加入 EGR 可以降低富氧燃烧下天然气发动机燃气消耗率，随着 EGR 率增加，燃气消耗率主要呈先减小后增加趋势；且随进气氧浓度提高，各浓度下最低燃气消耗率对应的 EGR 率逐渐提高；NOx 排放随EGR 率增加而逐渐降低，在进气氧体积分数为23％，25％，27％，29％时，EGR 率分别为10％，15％，20％，25％即可将 NOx 排放降到原机水平；利用进气富氧与 EGR 可以有效地改善天然气发动机动力不足与 NOx 排放高的状况。%The coupled simulation model of CNG engine was built with GT-Power and Converge software based on a 1.0 L gasoline engine and was calibrated with test data of original engine.Then the influences of oxygen-rich intake and EGR on CNG engine perform-ance were researched and the performance improvements thereof were discussed.The results show that BMEP for CNG engine increases obviously with the increase of oxygen volume fraction and increases by 22.8% at most in 28% oxygen content.Moreover,the in-cylin-der temperature,NOx emission,the energy loss of exhaust and heat transfer all increase and BSFC slightly increases.The specific CNG consumption under the conditions of rich oxygen decreases by introducing EGR and shows the trend of first decrease and following in-crease with the increase of EGR rate.The corresponding EGR rate of the lowest CNG consumption increases gradually with the increase of oxygen content.NOx emission increases with the increase of EGR rate and can reach the emission level of original engine when the EGR rate is 10%,15%,20% and 25% respectively in oxygen volume fraction of 23%,25%,27% and 29%.Accordingly,the oxy-gen-rich intake and EGR can improve the power and NOx emission of CNG engine effectively.