Ignition and Combustion Enhancement of Transient Fuel Spray by Plasma Jet

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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.