Effect of diesel pre-injection timing on combustion and emission characteristics of compression ignited natural gas engine
Effect of diesel pre-injection timing on combustion and emission characteristics of compression ignited natural gas engine
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DOI：
10.1016/j.enconman.2016.02.054
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发表时间：
2016-06
影响因子：
10.4
通讯作者：
Min Xu;Wei Cheng;Hongfei Zhang;T. An;Shaohua Zhang
中科院分区：
文献类型：
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作者：
Min Xu;Wei Cheng;Hongfei Zhang;T. An;Shaohua Zhang
预喷策略被认为是改善柴油机性能、排放和燃烧的重要途径之一。在先导柴油机压燃式天然气发动机中，它也是同样重要的因素。在一台由涡轮增压六缸柴油机改造而成的内燃机上，实验研究了预喷正时对燃烧和排放性能的影响。实验在1400 rpm恒定转速和1100 bar恒定燃油喷射压力下，在不同发动机负荷下进行。在预喷正时的推进过程中，将主喷正时固定在10°CA下止点。分析了气缸压力、心脏释放率（HRR）、压力上升率（PRR）、燃烧启动率（SOC）和变化系数（COVIMEP），以及NOx、HC和CO排放量。结果表明，紧密的预喷操作导致SOC提前，加剧了缸内混合气的燃烧，从而提高了缸内压力、HRR和PRR，提高了nox排放量，降低了HC和CO排放量。然而，由于燃烧强度降低，提前预喷操作会导致气缸压力、HRR和PRR降低。70°CA BTDC预喷时刻是预喷燃料对天然气点火和燃烧影响几乎消失、nox排放最低的转换点。与单喷射点火方式相比，在发动机负荷为38%、60%和80%时，转换点nox排放量分别降低33%、38%和7%。这对于由于喷油器的冷却需求而无法进一步降低燃料量以减缓缸内燃烧和nox排放的情况具有重要意义。此外，HC和CO排放量与单喷点火模式基本保持在同一水平，在部分负荷工况下甚至有一定的降低，说明早期预喷定时策略对降低nox排放是有效的。
Pre-injection strategy is considered to be one of the most important ways to improve diesel engine performance, emission and combustion. It is the same important factor in pilot diesel compression ignition natural gas (CING) engine. In this study, effects of pre-injection timing on combustion and emission performances were experimentally studied in a CING engine which was modified from a turbocharged six-cylinder diesel engine. The experiments were conducted at constant speed of 1400 rpm and different engine loads with a constant fuel injection pressure of 1100 bar. Main injection timing was fixed at 10 °CA BTDC in the advance process of pre-injection timing. The cylinder pressure, heart release rate (HRR), pressure rise rate (PRR), start of combustion (SOC) and coefficient of variation (COVIMEP), as well as NOx, HC and CO emissions were analyzed. The results indicated that closely pre-injection operations lead to the advance of SOC which intensified combustion of in-cylinder mixture, thereby resulting in higher cylinder pressure, HRR and PRR, as well higher NOxemissions and lower HC and CO emissions. However, early pre-injection operations lead to lower cylinder pressure, HRR and PRR due to decreasing in combustion intensity. Pre-injection timing of 70 °CA BTDC is a conversion point in which influence of pre-injection fuel on ignition and combustion of natural gas nearly disappeared and lowest NOxemission could be obtained. Compared with single injection ignition mode, NOxemissions at the conversion point were reduced by 33%, 38% and 7% at engine load of 38%, 60% and 80% respectively. This is important for the conditions that ignition fuel quantity cannot be further reduced to slow in-cylinder combustion and NOxemission due to cooling demand of fuel injector. In addition, HC and CO emissions almost maintained in the same level as single injection ignition mode, and even have a certain reduction for some of load conditions, which indicated that early pre-injection timing strategy is effective in reducing NOxemissions.