不同点火时刻下天然气掺氢缸内直喷发动机燃烧与排放特性

Combustion and Emission Characteristics of a Direct-Injection Engine Fueled with Natural Gas/Hydrogen Blends under Various Ignition Timings

在缸内直喷火花点火发动机上开展了天然气掺混0％-18％氢气的混合燃料不同点火时刻下的试验研究。结果表明:对于给定的喷射时刻和喷射持续期,点火时刻对发动机性能、燃烧和排放有较大影响,喷射结束时刻与点火时刻的间隔对直喷天然气发动机极为重要,喷射结束时刻与点火时刻的间隔缩短时,混合气分层程度高,燃烧速率快,热效率高。最大放热率等燃烧特征参数随点火时刻的提前而增加。HC排放随点火时刻的提前而下降,CO2和NOx排放随点火时刻的提前而增加,NOx排放的增加在大点火提前角下更明显。掺氧可降低HC排放,对CO和CO2排放影响不大。掺氢量大于10％时可提高天然气发动机热效率。

In this paper, an experimental study on combustion and emission characteristics in a direct-injection spark-ignited engine fueled with CNG/hydrogen blends under various ignition timings was investigated. The results show that the ignition timing has significant influence on engine performance, combustion and emissions. The interval between the end of fuel injection and ignition timing is a very important parameter of the direct-injection natural gas engine. The turbulence flow in combustion chamber generated by the fuel jet maintains high and relative strong mixture stratification is presented when decreasing the interval between the end of injection and the ignition timing, giving fast burning rate and high thermal efficiency. The maximum rate of heat release increase with the adwmce of ignition timing and it gives little variation with hydrogen addition under the same ignition timing. This indicated that hydrogen addition has little influence on combustion parameters at the constant ignition timing. The exhaust HC emission decrea- ses and the exhaust CO2 concentration increases with the advance of ignition timing. At the same ignition timing, the exhaust HC decreases with hydrogen addition while the exhaust CO and CO2 show little variation with hydrogen addition. The exhaust NOx increases with the advance of ignition timing and this behavior tends to be more obviously at large ignition advance operating condition. The effective thermal efficiency of CNG/hydrogen mixture combustion increases compared to these of natural gas combustion when hydrogen fraction is over 10%.