Experimental Study on Ignition Process of a Magnesium-Based Water Ramjet Engine

摘要

To start a water ramjet engine, the ignition energy needs to not only ignite the solid grain, which then produces molten metal particles, but also evaporate the injected water right after the ignition; the continuing operation of the engine is based on the sustained combustion between the molten metal particles and the water steam. A certain ignition pressure must be reached to generate the combustion. Along with the starting of the engine, a series of events are taking place inside, such as explosion of the igniter, preliminary combustion of the solid propellant, evaporation of the water droplets, mixing and reaction between water steam and metal particles, and so on. The starting sequence of the engine needs to be set up properly, so that the internal events can proceed smoothly toward a stable and full combustion. A wrong sequence may bring about a prolonged ignition process, or even extinction of the flame. As for a successful ignition of the water ramjet engine, the ignition process can be divided into four phases: ignition time lag, self-supporting precombustion interval, primary precombustion interval, and chamber-filling interval. The ignition performance of the engine is also affected by the water/fuel ratio, especially the primary water/fuel ratio. If the primary water/fuel ratio is too large or too small, it goes against the reduction of the ignition delay time. For a quick and effective ignition, an optimum primary water/fuel ratio should be chosen.