Ignition and Combustion Enhancement of Transient Fuel Spray by Plasma Jet

为了弄清等离子射流对瞬时燃油喷雾的点火能力及其助燃效果，在定容燃烧室上进行了燃烧试验。在试验中，使用了最大旋流速度为10m/S的稀甲烷-空气混合物。从纹影照片来看，在等离子射流点火的情况下，等离子体射流形成的火焰的湍流羽流通过旋转运动向燃烧室中心移动，在那里发生了后续的火焰发展。结果表明，等离子射流点火初期燃烧压力上升较快，但之后压力上升较慢。为此，研制了一种新型的等离子体射流点火器，其空腔被投射到燃烧室中。采用该投影式等离子点火器，利用投影腔的稳燃作用，使整个燃烧过程都有助燃效果，在密闭燃烧室内注入气态甲烷，尝试用等离子点火器点燃该瞬时燃油喷雾，但点火可能性很低。因此，我们尝试使用脉冲喷射点火燃烧发生器。该发生器的形状与等离子射流点火器相同，但在空腔中引入了丰富的混合物，并使用普通的电点火系统对空腔中的混合物进行点火。通过燃烧试验发现，脉冲射流燃烧发生器在整个燃烧过程中，尤其是燃烧后期都具有一定的助燃效果。这既是由点火前从孔口喷出的湍流未燃烧混合气引起的，也是由点火后从孔口喷出的湍流火焰引起的。

In order to make clear both the ignition ability of the plasma jet to the transient fuel spray and its combustion enhancement effects, combustion tests were carried out using the constant volume combustion chamber. In the tests, lean methane-air mixtures, which had the maximum swirl speed of 10m/s, were used. From the schlieren photographs, in the case of plasma jet ignition, the turbulent plume of the flame formed by the plasma jet was moved toward the center of the combustion chamber by the swirl motion, where the subsequent flame development occurred. As the result, the rapid combustion pressure rise was obtained by the plasma jet ignition in its initial period, however, after that, the combustion pressure rise was slower than that by the conventional spark ignition. So, the new type of plasma jet igniter, the cavity of which was projected into the combustion chamber, was made. Using this projected type of plasma jet igniter, flame holding effect by the projected cavity was obtained, and it made the combustion enhancement effects during the whole combustion period.Gaseous methane was injected into the closed combustion chamber, and this transient fuel spray was tried to be ignited by the plasma jet igniter, however, the possibility of the ignition was very low. Therefore, we tried to use the pulsed jet ignition combustion generator. The shape of this generator was just as same as the plasma jet igniter, however, the rich mixture was introduced into the cavity, and the ordinary electrical ignition system was used to ignite the mixture in the cavity. From the combustion tests, we found that the pulsed jet combustion generator has the combustion enhancement effects throughout the whole combustion period, especially its later period of the combustion. This was caused both by the turbulent unburned mixture issued from the orifice before the ignition and the turbulent flame injected from the orifice after the ignition.