国六重型柴油机排气热管理技术

李明星¹，张腾^2*，邹利宁²，周承忠¹，黎幸荣¹

1.广西玉柴机器股份有限公司，广西 玉林  537005；2.长城汽车股份有限公司，河北 保定  071000

摘要：为有效提高发动机排气温度和选择性催化还原器（selective catalytic reduction，SCR）入口温度，以某款国六重型柴油机为研究对象，根据排气温度分布特征将缸内燃烧控制区域划分为若干区间，每个区间制定差异化的温度控制策略；通过试验验证进气节流阀调控和燃烧参数优化两种排气热管理技术的效果，在此基础上设计集成了SCR自动加热模式的发动机自适应排气热管理策略，并开展发动机台架冷态世界统一瞬态循环（world harmonized transient cycle，WHTC）试验和高原复杂路况实车验证试验，评估热管理策略的实际效果。结果表明：后喷油量、后喷正时对排气温度的影响明显大于轨压、主喷正时、预喷正时；后喷油量和后喷正时增大，排气热管理效果逐步增强；当进气节流阀的关闭度不低于70%时，排气温度随进气节流阀的关闭度增大呈升高趋势；发动机在中、高负荷运行时，可以通过优化后喷油量和后喷正时等燃烧参数的方法达到较好的热管理效果；低负荷及0负荷工况下，通过进气节流阀调控并耦合优化燃烧参数的策略可以实现良好的排气热管理效果；冷态WHTC工况下，发动机平均排气温度提高约20 ℃，在WHTC加权平均油耗增长率仅为4%的前提下，NO_x比排放大幅降低（降幅约为30%）；高原长下坡工况下，SCR入口温度可长时间维持在370 ℃左右。设计的自适应排气热管理策略可使发动机在冷机、高原、低温等恶劣工况下具有良好的热管理效果。

关键词：柴油机；排气热管理；SCR；燃烧参数；进气节流阀

Exhaust thermal management technology for a CHINA Ⅵ heavy-duty diesel engine

LI Mingxing¹, ZHANG Teng^2*, ZOU Lining², ZHOU Chengzhong¹, LI Xingrong¹

1.Guangxi Yuchai Machinery Co., Ltd., Yulin 537005, China; 2.Great Wall Motor Co., Ltd., Baoding 071000, China

Abstract: In order to effectively improve the engine exhaust temperature and selective catalytic reduction (SCR) inlet temperature, a certain China VI heavy-duty diesel engine is taken as the research object. Based on the distribution characteristics of exhaust temperature, the combustion control area in the cylinder is divided into several intervals, and differentiated temperature control strategies are formulated for each interval. Based on the experimental verification of the effects of two exhaust thermal management technologies, namely intake throttle valve regulation and combustion parameter optimization, an adaptive exhaust thermal management strategy for the engine integrated with SCR automatic heating mode is designed. Engine bench cold world unified transient cycle (WHTC) tests and high-altitude complex road condition real vehicle verification tests are conducted to evaluate the actual effectiveness of the thermal management strategy. The results show that the influence of post injection quantity and post injection timing on exhaust temperature is significantly greater than that of rail pressure, main injection timing, and pre-injection timing. Furthermore, as the post injection quantity and timing increase, the exhaust thermal management effect gradually strengthens. When the closing degree of the intake throttle valve is not less than 70%, the exhaust temperature shows an upward trend with the increase of the closing degree of the intake throttle valve. When the engine operates at medium to high loads, it can achieve good thermal management effects by optimizing combustion parameters such as fuel injection quantity and timing. Under low load and zero load conditions, the strategy of regulating and coupling combustion parameters through the intake throttle valve can achieve good exhaust thermal management effects. Under cold WHTC conditions, the average exhaust temperature of the engine increases by about 20 ℃. With a weighted average fuel consumption growth rate of only 4% in cold WHTC, the NO_x specific emissions are significantly reduced (by about 30%). In the case of long downhill slopes on the plateau, the inlet temperature of SCR can be maintained at around 370 ℃ for a long time. The designed engine adaptive exhaust thermal management strategy can enable the engine to have good thermal management effects in harsh working conditions such as refrigeration, high altitude, and low temperature.

Keywords: diesel engine; exhaust thermal management; SCR; combustion parameter; intake throttle valve