﻿ 柴油引燃缸内直喷天然气发动机燃烧和排放特性研究
 舰船科学技术  2018, Vol. 40 Issue (3): 97-101 PDF

Research of combustion and emission characteristics in pilot ignited directly injected natural gas engine
ZHANG Heng, GONG Xi-wu
School of Naval Architecture and Mechanical-electrical Engineering, Zhejiang Ocean University, Zhoushan 316022, China
Abstract: In order to study the effect of injection timing on the marine dual fuel engine, the AVL-FIRE was used to do the simulation on the different injection timing under fixed injection interval. The results show that, with the delay of natural gas injection, the mean pressure peaks and the mean temperature peaks in the cylinder gradually reduced, which reduces the mechanical load and the thermal load of the engine. When the injection time of nature gas is in TDC, the sum of time of rapid combustion and slow combustion is shortest, the combustion process is the fastest. NOx emissions obviously reduce with the injection timing delay. Therefore, it is benefit to optimize the emissions by delaying the injection timing.
Key words: directly injection     natural gas engine     injection timing     combustion characteristic
0 引　言

1 实验装置及仿真模型 1.1 实验装置

1.2 仿真模型的建立

 图 1 180°、320°、360°仿真模型 Fig. 1 The simulation model of 180°、320°、360°
2 仿真的计算与分析 2.1 仿真方案

 $I = \frac{{{M_{{{diesel}}}} \times LH{V_{{{diesel}}}}}}{{{M_{{{diesel}}}} \times LH{V_{{{diesel}}}} + {M_{{{LNG}}}} \times LH{V_{{{LNG}}}}}} \times 100\%,$ (1)
 $\phi = \frac{{{M_{{{air}}}}}}{{{M_{{{diesel}}}} \times {L_{{{diesel}}}} + {M_{{{LNG}}}} \times {L_{{{LNG}}}}}}{\text{。}}$ (2)

2.2 不同喷射时刻对缸内压力和温度的影响

 图 2 喷射时刻对缸内平均压力的影响 Fig. 2 Effects of injection timing on mean pressure

 图 3 喷射时刻对缸内温度压力的影响 Fig. 3 Effects of injection timing on mean temperature

 图 4 喷射时刻对缸内平均压力峰值的影响 Fig. 4 Effects of injection timing on mean pressure peak
2.3 喷射时刻对温度场的影响

 图 5 喷射时刻对温度场的影响 Fig. 5 Effects of injection timing on temperature contours
2.4 喷射时刻对放热的影响

 图 6 喷射时刻对累积放热量的影响 Fig. 6 Effects of injection timing on accumulated heat release
2.5 喷射时刻对燃烧阶段的影响

 图 7 燃烧过程划分图 Fig. 7 The partition for duration of combustion

 图 8 喷射时刻对燃烧期的影响 Fig. 8 Effects of injection timing for the duration of combustion

2.6 喷射时刻对排放的影响

 图 9 喷射时刻对氮氧化物的影响 Fig. 9 Effects of injection timing for mean NO fraction

 图 10 喷射时刻对炭烟排放的影响 Fig. 10 Effects of injection timing for mean soot fraction
3 结　语

1）随着天然气喷射时刻的延后，各方案缸内平均压力峰值减小，平均压力峰值的减小量逐渐增大；缸内平均温度的峰值也逐渐减少，但减小趋势没有明显变化。可以通过推迟缸内燃料的喷射减小缸内压力峰值，抑制爆震的发生。

2）随着燃料喷射时刻的变化缸内各燃烧阶段的长短有明显变化，其中方案t4天然气于上止点位置喷入缸内，此时滞燃期最短，速燃期和缓燃期的时间和也最短，缸内燃烧最快。所以，上止点附近为天然气喷射较理想位置。

3）较晚的天然气喷射，缸内的燃烧更柔和，可以减少缸内的热负荷。

4）缸内氮氧化物的生产量随着天然气喷射时刻的推迟也相应减少，但是由于温度降低的原因，炭烟不能被很好氧化，其排放量稍有增加。应该进一步研究对氮氧化物和炭烟都有利的燃烧方案。

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