实现重型柴油机低排放的喷油策略及其与后处理耦合

Development of a Low-Emission HD Diesel Engine with Fuel Injection Strategy Coupled with After-Treatment System

在燃烧系统优化基础上,围绕燃油喷射参数与控制策略、EGR等参数对共轨重型柴油机燃烧与排放特性的影响机理展开深入研究,通过喷油策略优化并与后处理系统耦合实现重型柴油机低排放.研究表明:小负荷采用单次喷射并通过降低喷油压力与推迟喷油,可获得较低的NOx和soot排放,有效降低压力升高率;低转速大负荷通过降低喷油压力与推迟喷油定时相结合,在实现等NOx时能有效改善soot和油耗率;高转速中高负荷适宜提高喷射压力,采用主喷加后喷的多次喷油策略.欧洲稳态测试循环(ESC)测试结果表明:采用串联式两级增压与中等强度EGR(低于40%)耦合,NOx原始加权排放率降至欧Ⅴ水平;在依次加装氧化型催化器(DOC)、微粒捕集器(DPF)和选择性催化还原(SCR)后处理系统,通过喷油策略与后处理耦合,DPF的过滤效率高达90%,SCR转化效率达到85%,各项排放指标均满足欧Ⅵ的ESC限值要求,尿素喷射总量降至原机(国4的SCR机型)的1/4～1/5.

Based on combustion system optimization, an experimental study on the effects of fuel injection parameter and control strategy, as well as EGR on combustion and emission characteristics of a common-rail heavy-duty （HD）diesel engine was conducted. Results show that, at low loads, NOx and soot emissions, maximum rate of pressure rise （MPRR） are effectively reduced by lowering the injection pressure and postponing the injection timing with single injection strategy. At low speed and high load conditions, soot and BSFC are reduced simultaneously using the same control strategy as that at low loads. However, higher injection pressure and post injection are required to reduce the emissions and fuel consumption at high speed and middle to high load conditions. Results of ESC show that, NO~ weighted emissions are reduced to the level of Euro V by using two-stage turbocharger （2 TC） and medium EGR （〈 40%）. All emissions meet the limits of Euro 6 by the combination of DOC, DPF and SCR. The conversion efficiencies of DPF and SCR are 90% and 85% respectively. Meanwhile, urea consumption is reduced by one fourth to one fifth of the original level.