杜辉，江帆，邓水根，孔凡良.米勒循环及低压废气再循环技术对汽油机性能的影响研究[J].内燃机工程,2021,42(2):47-52.
米勒循环及低压废气再循环技术对汽油机性能的影响研究
Effects of Miller Cycle and Low-Pressure Exhaust Gas Recirculation on Gasoline Engine Performance
DOI：10.13949/j.cnki.nrjgc.2021.02.007
关键词:汽油机  米勒循环  废气再循环  经济性
Key Words:gasoline engine  Miller cycle  exhaust gas recirculation（EGR）  economy
基金项目:
作者单位
杜辉，江帆，邓水根，孔凡良 无锡沃尔福汽车技术有限公司，无锡 214000 
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摘要:在某2.0 L涡轮增压商用车缸内直喷汽油机概念设计阶段，运用GT Power软件进行了一维热力学计算分析，并着重研究了米勒循环技术与低压废气再循环（exhaust gas recirculation,EGR）技术对燃油经济性的影响。仿真结果显示，长米勒循环和短米勒循环都存在使燃油经济性达到最佳的可变气门正时角度。在中高转速范围内，因为质量流量和流速过高导致长米勒循环的缸内空气无法顺利回流，米勒效应减弱，所以短米勒循环的燃油经济性更好；另外长米勒循环具有两次泵气过程，致使其泵气损失也大于短米勒循环。在低转速范围内，短米勒循环的增压压力需求更大，导致其泵气损失大于长米勒循环，所以长米勒循环的燃油经济性更好。对于试验用汽油机来说，短米勒循环具有明显的优势。低压EGR技术能够使缸内最高温度降低，减轻爆震倾向，因此燃烧重心可以适当提前，从而改善燃油经济性。另外，EGR和新鲜空气总量的增加也使最高燃烧压力增大，有利于燃油经济性的提高。不同工况下，缸内最高温度均随EGR率的增加而降低,因此在一定范围内EGR率越高燃油经济性越好，涡前排温越低,但EGR冷却器需要的散热功率也增大。在发动机燃烧开发阶段，推荐采用短米勒循环技术并结合8%的EGR率。为了验证仿真结果的准确性，开展了性能试验，试验结果与仿真结果在趋势上有很好的一致性。
Abstract:In the conceptual design stage of a 2.0 L turbocharged gasoline engine for a commercial vehicle, one-dimensional thermodynamic calculation was carried out using GT-Power software and the influence was studied of the Miller cycle technology and low-pressure exhaust gas recirculation (EGR) technology on the fuel economy. The simulation results show that both long Miller cycle and short Miller cycle have the optimal VVT angles for the fuel economy. At medium-high-speed region, the fuel economy of the short Miller cycle is better, because in the long Miller cycle, the reversal of air flow in cylinder is not possible due to high mass flow and velocity, and the Miller effect is reduced. In addition, the long Miller cycle has two pumping processes, resulting in more pumping loss than the short Miller cycle. At low-speed region, the fuel economy of the long Miller cycle is better because the boost pressure of the short Miller cycle is higher, resulting in more pumping loss than the long Miller cycle. For this gasoline engine, the short Miller cycle has obvious advantages. The low-pressure EGR technology can decrease the maximum temperature in cylinder and reduce knock tendency, hence crank angle of 50% mass fraction burned(CA50) being advanced properly to optimize the fuel economy. Furthermore, the increase of the total amount of EGR and fresh air also leads to an increase in cylinder peak pressure, contributing to a better fuel economy. In different operating conditions, the maximum temperature in cylinder decreases with the growth of the EGR rate. Therefore, within a certain range, the higher the EGR rate, the better the fuel economy and the lower the turbine inlet temperature. However, in the meantime more cooling power is required by the EGR cooler. As a result, the short Miller cycle technology is applied for the engine combustion development process, and the recommended EGR rate is 8%. In order to verify the simulation results, the engine performance test was carried out, and the experimental results are in good agreement with the simulation results.
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