高低压废气再循环系统(EGR)对进气道喷醇式柴油甲醇双燃料发动机的影响

以一台加装了进气道喷醇系统（MIIA）、高低压废气再循环系统（EGR）的2.8 L增压中冷高压共轨直喷柴油机为平台，在不同负荷下开展不同外部EGR循环方式对进气道喷醇式柴油甲醇双燃料发动机性能影响的试验研究.结果表明，柴油甲醇组合燃烧（DMCC）技术对EGR技术具有良好兼容性.在采用国VI排放法规标准规定的稳态试验循环（WHSC）测试条件下，借助EGR技术的DMCC发动机氮氧化物（NO_x）排放会显著降低且颗粒物（PM）保持在较低水平，打破了NO_x-PM的trade-off关系.此外，不同EGR方式对排放特性、进排气参数、燃烧特性和经济性能的影响存在显著差异，耦合排气背压阀（BPV）后的低压EGR策略可实现更高的EGR率，将NO_x排放降至国VI限值附近.但同等EGR率下发动机采用高压EGR更具优势，利于均质混合气的形成，增加预混燃烧占比，获得更高的燃烧效率和热效率.然而受限于高EGR率需求，采用单一型式EGR策略实现DMCC发动机满足国VI限值仍存在困难.

Impact of high and low pressure EGR on diesel methanol dual fuel engine with methanol injected into intake port

A 2.8 L turbocharged inter-cooled high-pressure common rail direct injection diesel engine,which was equipped with a system of methanol injected in intake air (MIIA) and a high and low pressure exhaust gas recirculation (EGR), is used to carry out an experimental study on the effects of different external EGR methods on the performance of diesel-methanol dual fuel engine at different loads. The results show that DMCC technology has good compatibility with EGR technology. Under the condition of WHSC test method stipulated in the national VI emission regulation, NO_x emissions from DMCC engine with EGR are significantly reduced and PM remains low, breaking the trade-off relationship between NO_x and PM. In addition, there are significant differences in the effects of different EGR methods on emission characteristics, intake and exhaust parameters, combustion characteristics and economic performance. Combined with the back pressure valve (BPV), the low-pressure EGR can achieve higher EGR rates and reduce NO_x emissions to near the national VI limit. But high pressure EGR can facilitates the formation of homogeneous mixture, increases the proportion of premixed combustion and obtains higher combustion efficiency and brake thermal efficiency, which is better strategy for the same EGR rate. However, it is still difficult to achieve the national VI limit value for DMCC engines by using only a single type of EGR strategy due to the demand of high EGR rate.