基于柴油机排气热管理的喷油策略控制试验研究

为有效满足柴油机中低转速、中小负荷工况下颗粒捕集器(DPF)主动再生时的工作温度需求,利用发动机台架试验研究了中低负荷稳态工况下主喷正时、近后喷及次后喷参数等排气热管理主动控制措施对缸内燃烧过程、排气热状态及排放性能的影响规律。稳态试验结果表明:推迟主喷提前角缩短了滞燃期,燃烧持续期延长,缸内最高燃烧压力及峰值温度下降,瞬时放热率峰值减小且燃烧重心后移,同时燃油消耗率及烟度略有增加,DOC入口温度提升也不明显;引入近后喷使得缸内最高燃烧压力降低,但放热率第二峰值及后燃期有所增加,近后喷油量与主-近后喷间隔角的合理匹配能适当提高DOC入口温度,最高增幅可达19.3%,同时也能有效改善NOx排放和烟度;次后喷油量的增加能显著提升DPF入口温度,最大增幅达70%,但会导致燃油消耗率及HC逃逸量增加。依据样机全工况排温分布状态提出各区域升温喷油控制策略:低负荷区域采用"近后喷+次后喷"的喷油组合,并且采用较大喷油量;中大负荷区域逐渐减少近后喷,直至无近后喷,同时将主喷适当提前。

Fuel Injection Control Strategy Based on Exhaust Thermal Management of Diesel Engine

In order to effectively meet the working temperature requirements of DPF active regeneration under medium-low speed and load conditions,engine bench test was used to study the influences of active control measures such as main injection timing,near post injection and late post injection parameters on in-cylinder combustion process,exhaust thermal status and e-mission performance under the medium and low load steady state conditions.The steady test results showed that the ignition delay period shortened,the combustion duration prolonged,the in-cylinder maximum combustion pressure and peak tempera-ture decreased,the instantaneous heat release rate dropped,the center of gravity shifted back,BSFC and smoke increased slightly and the temperature of DOC inlet rose little after main injection timing delayed.The introduction of near post injection reduced the peak combustion pressure,but the second peak value of instantaneous heat release rate and post combustion period increased.In addition,the reasonable matching of near post injection quantity and angle between main and near post injection could improve the inlet temperature of DOC properly,and the highest increase was up to 19.3%.It could also effectively im-prove smoke and NO xemission.The increase of late post injection quantity could significantly increase the inlet temperature of DPF by up to 70%,but it would lead to an increase in BSFC and HC escape.According to the distribution state of exhaust tem-perature in the whole working condition of prototype engine,the strategy of temperature-rising injection control in each region was proposed.The low load area adopted fuel injection combination of near and late post injection accompanied with a large a-mount of fuel injection.At medium and high load area,the near post injection reduced step by step and finally stopped,and the main injection advanced appropriately at the same time.