二甲醚在发动机气缸内喷雾燃烧过程的实验研究

Experimental Study on the Spray and Combustion Process of Dimethyl Ether in Cylinders

在可视化光学发动机上进行了二甲醚(DME)喷雾燃烧过程的试验,应用高速数字摄像机拍摄了柴油和二甲醚缸内喷雾燃烧过程,并应用计算机高速采集系统同步测量了缸内压力.高速摄影照片表明,二甲醚一离开喷嘴就迅速蒸发,可以明显看到缸内气流运动对油速"核心"的吹散作用,并造成二甲醚的碰壁油量较柴油的少.和柴油相比,二甲醚着火滞燃期短,着火位置更靠近燃烧室壁面,着火面大,燃烧初期火焰发展迅速.二甲醚压升滞燃期比发火滞燃期明显减小,而柴油两者几乎相等.在相同热值燃料条件下,发动机燃用柴油和二甲醚时,缸内最大爆发压力、燃烧放热率和平均指示压力几乎一样.高速摄影很难拍摄到二甲醚燃烧初期和后期的火焰照片.研究结果还表明,较小的涡流比有利于提高二甲醚发动机的性能.

The study on spray and combustion process of dimethyl ether (DME) was carried out on an optical seethrough engine, and the photographs of spray and combustion of DME were taken by high speed digital CCD. The heat release rate, average temperature and indicated mean effective pressure were calculated by using zerodimensional model according to the measured incylinder pressure data. The results of highspeed photograph show that, as soon as DME leaves the nozzle, it evaporates rapidly, and under the effect of air swirl, the spray'core' is blown off . The penetration of DME is shorter than that of diesel, and the wall combustion of DME is apparently smaller than that of diesel. Compared to diesel, DME has shorter ignition delay, the ignition position is nearer the wall, the area of ignition is larger at the beginning of combustion, and the flame propagates faster. The pressure delay of DME is shorter than the illumination delay, while the pressure delay of diesel is almost the same as the illumination delay. The cylinder pressure, the heat release rate and the average gas temperature are almost the same for both fuels. The combustion duration calculated by the cylinder pressure is almost the same for both fuels while the photographs indicate that DME has shorter combustion duration. Therefore, the luminous flame of DME is hardly discerned at both the beginning and the later stage of combustion. Meanwhile DME and diesel have almost the same thermal efficiency. The results also show that small air swirl ratio has an active effect on engine performance.