Experimental study on the effects of supercharging system,combustion chamber and injector,as well as EGR on combustion process,performance and emissions,was conducted on a common-rail heavy-duty (HD)diesel engine.Results show that the two-stage turbocharger (2 TC)can obviously enhance EGR recyclability and improve the trade-off relationships of NOx-soot and NOx-BSFC as compared to the single-stage turbocharger at low to middle speed and high load conditions.Soot,BSFC and the maximum in-cylinder pressure can be decreased by properly reducing compression ratio,optimizing structure parameters of combustion chamber (reentrant diameter and bowl depth)as well as using the injectors with taper holes.Experimental study on China Stage 4 of diesel engine with EGR technology was performed.Results of ESC cycle test show that,with increasing power density,2 TC is superior to single turbocharger in terms of emissions and fuel economy.All emissions can meet the limits of China Stage IV for the engine of 29.8 kW/L using 2 TC without any after-treatment device,and the weighted BSFC is only 3％ higher than that of the original engine.Thus,2 TC is more suitable for HD diesel engine with high power density to achieve China Stage IV without after-treatment system.%针对一台共轨重型柴油机,围绕进气增压系统、燃烧室与喷油器结构参数和EGR参数等因素对重型柴油机燃烧过程、性能和排放特性的影响机理展开深入研究.结果表明,随转速降低和负荷增加,两级增压相比单级增压能明显提高EGR循环能力和空燃比,有效改善NOx与燃油消耗率(BSFC)以及NOx与碳烟之间的trade-off关系.通过合理降低燃烧室压缩比、优化设计燃烧室结构参数(缩口直径、凹坑深度)并采用带倒锥度喷孔喷油器,能同时有效改善碳烟和BSFC并降低缸内最大燃烧压力至合理水平.国4的欧洲稳态测试循环结果表明,随升功率增加,两级增压相比单级增压在性能和排放方面逐渐表现出明显优势.对于29.8 kW/L的功率段,两级增压耦合EGR在无后处理下使各项排放指标均满足国4限值要求,十三工况加权BSFC相对基于选择催化还原(SCR)技术的国4柴油机仅增加3％左右.因此,两级增压是基于EGR技术的高升功率柴油机实现无后处理国4排放的一项有效燃烧优化技术.
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