Detailed Heat Release Analyses with Regard to Combustion of RME and Oxygenated Fuels in an HSDI Diesel Engine
Detailed Heat Release Analyses with Regard to Combustion of RME and Oxygenated Fuels in an HSDI Diesel Engine
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关于 HSDI 柴油发动机中 RME 和含氧燃料燃烧的详细放热分析
DOI：
10.4271/2007-01-0627
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Ö. Andersson
中科院分区：
文献类型：
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作者：
Uwe Horn;R. Egnell;B. Johansson;Ö. Andersson
在一台现代直喷式柴油机上进行了试验：在低负荷条件下（4巴IMEP），发动机燃用标准柴油、RME以及85%标准柴油、5% RME和10%高级醇的混合物。在这些实验中，应用不同的外部EGR水平，同时以保持50%放热位置恒定的方式选择喷射正时。排放分析结果与众所周知的相关性一致：增加EGR率降低NOx排放。这是由全球空燃比的减少，需要更长的点火延迟解释。滞燃期内局部气燃比增大，局部燃烧温度降低。废气分析进一步表明，在高EGR水平下，CO、PM和未燃HC排放强烈增加。这导致了较低的燃烧效率。然而，PM排放量下降超过50% EGR，这也与先前报告的结果一致。除了这些类似的趋势，燃料依赖的指示热效率以及CO，HC，NOx，特别是PM排放的差异进行了观察。通过详细的放热分析和基于燃料特性（如燃料粘度和燃料蒸馏曲线）的解释模型来评估这些差异。燃油喷雾的蒸发和放热特性受燃油特性的影响。由于这些特征，得出结论，RME在低负荷条件下比其他测试燃料类型更倾向于形成富油区。此外，发现改进的燃料喷雾蒸发是在低负载条件下改进废气排放的一种选择。（减）
Experiments on a modern DI Diesel engine were carried out: The engine was fuelled with standard Diesel fuel, RME and a mixture of 85% standard Diesel fuel, 5% RME and 10% higher alcohols under low load conditions (4 bar IMEP). During these experiments, different external EGR levels were applied while the injection timing was chosen in a way to keep the location of 50% heat release constant. Emission analysis results were in accordance with widely known correlations: Increasing EGR rates lowered NOx emissions. This is explained by a decrease of global air-fuel ratio entailing longer ignition delay. Local gas-fuel ratio increases during ignition delay and local combustion temperature is lowered. Exhaust gas analysis indicated further a strong increase of CO, PM and unburned HC emissions at high EGR levels. This resulted in lower combustion efficiency. PM emissions however, decreased above 50% EGR which was also in accordance with previously reported results. Besides those similar trends, fuel dependent differences in indicated thermal efficiency as well as CO, HC, NOx and especially PM emissions were observed. These differences were evaluated by detailed heat release analysis and explanation models based upon fuel characteristics as fuel viscosity and fuel distillation curve. Fuel spray evaporation and heat release were influenced by these fuel characteristics. Due to these characteristics it was concluded that RME has a higher tendency to form fuel rich zones at low load conditions than the other tested fuel types. Moreover it was found that improved fuel spray vaporisation is an option to improve exhaust emissions at low load conditions. (Less)