Evaluation of low-temperature diesel combustion regimes with n-Heptane fuel in a constant-volume chamber

The concept of Low Temperature Combustion (LTC) has been advancing rapidly because it may reduce emissions of NOx and soot simultaneously. Various LTC regimes that yield specific emissions have been investigated by a great number of experiments. To accelerate the evaluation of the spray combustion characteristics of LTC, to identify the soot formation threshold in LTC, and to implement the LTC concept in real diesel engines, LTC is modeled and simulated. However, since the physics of LTC is rather complex, it has been a challenge to precisely compute LTC regimes by applying the available diesel combustion models and considering all spatial and temporal characteristics as well as local properties of LTC. In this paper, LTC regimes in a constant-volume chamber with n-Heptane fuel were simulated using the ECFM3Z model implemented in a commercial STAR-CD code. The simulations were performed for different ambient gas O₂ concentrations, ambient gas temperatures and injection pressures. The simulation results showed very good agreement with available experimental data, including similar trends in autoignition and flame evolution. In the selected range of ambient temperatures and O₂ concentrations, soot and NOx emissions were simultaneously reduced.     

进气预混甲醇降低柴油机碳烟与NOx排放的影响参数研究

在485QDI自然吸气直喷式柴油机上研究了不同喷嘴、不同供油定时、不同喷醇的起点对进气预混甲醇发动机的碳烟、NOx排放和经济性的影响。研究结果表明，为了降低碳烟和NOx排放以及提高燃油经济性，与燃用纯柴油的发动机相比，进气预混甲醇发动机的柴油喷射定时可以保持不变或稍小，但燃油喷嘴的孔径应适当减小，预混甲醇的发动机负荷起点应适中。     

均质GDI汽油机混合气形成的影响因素研究

文中以一款增压直喷汽油机燃烧系统开发为例,从低速及高速两种工况,研究了气道及燃烧室形状、油束布置方案等因素对缸内混合气形成过程的影响。分析结果显示改变进气道及燃烧室屋脊形状、增加缸盖排气侧挤气面积以及调整油束喷射角度,可以提高缸内滚流运动强度、加强油气混合过程,从而有效改善了点火前缸内混合气的分布情况。研究了高转速下喷油时刻对混合气形成及燃油湿壁情况的影响,结果显示喷油起始角为390°CA时综合效果较好。采用较优方案组合进行的初步性能试验表明,外特性及部分负荷工况下的燃烧效率较高,动力性及经济性基本达到既定目标。     

缸内喷雾燃烧CFD仿真模型校验

摘要：采用AVLFIRE软件,对某重型柴油发动机进行缸内喷雾燃烧过程仿真。利用内窥镜系统,获得缸内喷雾燃烧图像。通过CFD仿真结果与喷雾过程、燃烧火焰、碳烟浓度分布进行定性对比分析,校验了缸内喷雾燃烧CFD仿真模型的准确性。     

Development of quantitative measuring technique to find critical flow conditions for preventing soot deposit accumulated in the diesel exhaust system using main muffler composed of three chambers

If a vehicle that meets emission regulations operates sufficiently for a long time under low speed and low load conditions, soot contained in the exhaust gas is accumulated on the inner surface of the exhaust system. This soot deposition problem occurs frequently in all diesel cars. However, when a vehicle is placed under the conditions of sudden start and sudden acceleration after city mode driving for a long time, the deposited soot is abruptly blown up with the soot produced during fuel combustion. In the present study, the main cause of the abrupt outburst of deposited soot is investigated to overcome this adverse phenomenon. First, we developed a method to quantify the amount of the exhausted soot particles (or the accumulated soot particles) by measuring the opacity that represents the contamination level of the exhaust gas due to soot particles. Using this measuring scheme for deposited soot, we found the critical conditions for engine speeds and load conditions at which soot particles are emitted into the air without accumulation in the exhaust system using main muffler composed of three chambers. In order to meet these critical conditions and thus to drastically reduce soot accumulation, the exhaust system using the main muffler applied in this study must be designed to ensure that the flow velocity of the exhaust gas is higher than 62 m/s when the back pressure at the exit of the turbocharger is under 0.08 bars.