Lamani Venkatesh Tavareppa, Yadav Ajay Kumar, Narayanappa Kumar Gottekere
Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal, Mangalore, 575 025, India.
Environ Sci Pollut Res Int. 2017 Jun;24(18):15500-15509. doi: 10.1007/s11356-017-9113-3. Epub 2017 May 16.
Due to presence of more oxygen, absence of carbon-carbon (C-C) bond in chemical structure, and high cetane number of dimethyl ether (DME), pollution from DME operated engine is less compared to diesel engine. Hence, the DME can be a promising alternative fuel for diesel engine. The present study emphasizes the effect of various exhaust gas recirculation (EGR) rates (0-20%) and DME/Diesel blends (0-20%) on combustion characteristics and exhaust emissions of common rail direct injection (CRDI) engine using three-dimensional computational fluid dynamics (CFD) simulation. Extended coherent flame model-3 zone (ECFM-3Z) is implemented to carry out combustion analysis, and k-ξ-f model is employed for turbulence modeling. Results show that in-cylinder pressure marginally decreases with employing EGR compared to without EGR case. As EGR rate increases, nitrogen oxide (NO) formation decreases, whereas soot increases marginally. Due to better combustion characteristics of DME, indicated thermal efficiency (ITE) increases with the increases in DME/diesel blend ratio. Adverse effect of EGR on efficiency for blends is less compared to neat diesel, because the anoxygenated region created due to EGR is compensated by extra oxygen present in DME. The trade-off among NO, soot, carbon monoxide (CO) formation, and efficiency is studied by normalizing the parameters. Optimum operating condition is found at 10% EGR rate and 20% DME/diesel blend. The maximum indicated thermal efficiency was observed for DME/diesel ratio of 20% in the present range of study. Obtained results are validated with published experimental data and found good agreement.
由于二甲醚（DME）中存在更多的氧、化学结构中不存在碳-碳（C-C）键以及十六烷值高，与柴油发动机相比，使用DME的发动机污染更少。因此，DME有望成为柴油发动机的替代燃料。本研究利用三维计算流体动力学（CFD）模拟，强调了各种废气再循环（EGR）率（0-20%）和DME/柴油混合比（0-20%）对共轨直喷（CRDI）发动机燃烧特性和废气排放的影响。采用扩展相干火焰模型-3区（ECFM-3Z）进行燃烧分析，采用k-ξ-f模型进行湍流建模。结果表明，与无EGR情况相比，采用EGR时缸内压力略有下降。随着EGR率的增加，氮氧化物（NO）的生成减少，而碳烟略有增加。由于DME具有更好的燃烧特性，指示热效率（ITE）随着DME/柴油混合比的增加而提高。与纯柴油相比，EGR对混合燃料效率的不利影响较小，因为EGR产生的缺氧区域被DME中存在的额外氧气所补偿。通过对参数进行归一化，研究了NO、碳烟、一氧化碳（CO）生成和效率之间的权衡。最佳运行条件为10%的EGR率和20%的DME/柴油混合比。在本研究范围内，DME/柴油比为20%时观察到最大指示热效率。将获得的结果与已发表的实验数据进行验证，发现吻合良好。
