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在一台光学高速直喷柴油机上采用多级喷射方法进行了低温压缩发火燃烧研究。对放热特点进行了分析。通过对自然火焰光度摄像,实现了整个循环燃烧过程可视化。测量了排气管内的NOx排放值,分析了引喷定时、引喷燃油量、主喷定时、运行负荷以及喷射压力对燃烧和排放的影响。低温燃烧模式是通过采用喷射定时远在上止点之前的小量引喷及随后在上止点之后的主喷来实现的。试验结果与传统柴油机(扩散)燃烧进行了对比。在所有低温燃烧下观察到以预混合为主的放热率曲线模式,而在传统燃烧方案下观察到典型的扩散火焰燃烧放热率模式。在传统的燃烧条件下观察到高亮度火焰,而在低温燃烧方案下观察到亮度低得多的火焰。在较高负荷和喷油量较低的方案,观察到在有些方案下有液态燃油喷入低温预混合火焰中。与传统扩散燃烧相比,低温燃烧在相似的运行负荷下取得了碳烟和NOx同时降低的效果。对于高负荷条件,由于缸内温度较高,NOx排放量较大。不过,与传统燃烧相比,高负荷条件下碳烟量有明显降低,这表明,增大喷射压力可显著减少碳烟排放量。
In a high-speed optical direct injection diesel engine using multi-stage injection method for low temperature compression ignition combustion research. The exothermic characteristics were analyzed. Through the natural flame photometric imaging, to achieve the entire cycle of combustion process visualization. The NOx emissions in the exhaust pipe were measured. The influences of pilot injection timing, pilot fuel injection, main injection, operating load and injection pressure on combustion and emissions were analyzed. The low temperature combustion mode is achieved by using a small injection of injection timing far before top dead center and then main injection after top dead center. The test results are compared with conventional diesel (diffusion) combustion. The predrying heat release rate profile was observed at all low temperature combustion, whereas the typical pattern of diffusion flame heat release was observed under the conventional combustion scheme. High-brightness flames were observed under traditional combustion conditions, while flames of much lower brightness were observed under low-temperature combustion schemes. At higher loads and lower fuel injection rates, it was observed that in some scenarios liquid fuel was injected into the low-temperature premixed flame. Compared with conventional diffusion combustion, low temperature combustion achieved the same effect of reducing both soot and NOx at similar operating loads. For high load conditions, NOx emissions are greater due to higher cylinder temperatures. However, there was a significant reduction in soot volume under high-load conditions compared to conventional combustion, indicating that increasing injection pressure significantly reduces soot emissions.