| OCR Text |
Show - 4 - lowers the pressure in the system until the combustion chamber pressure is below that maintained in the intake fuel and air lines. When this negative pressure differential occurs, some fresh air and fuel is introduced into the combustion chamber. Not all of the residual reaction products are flushed out of the system. In order for spontaneous reignition of the fresh reactants to occur, enough hot reaction products must remain to raise the temperature of the reactants to a point where they will themselves be able to ignite. This reignition then provides the heat release to drive another combustion cycle. There are several physical and chemical processes which are of particular importance in this system. One concerns the mixing of the inducted fresh fuel and air with the hot reaction products. The spatial orientation of the intake fuel and air lines, the relative pressures which is maintained in the intake lines, and the geometry of the mixing region of the combustion chamber are all known to play roles in the behavior of the pulse combustor. This turbulent mixing process is not well characterized at present and is a serious limitation to a more complete understanding of the pulse combustor. A second problem involves a description of the fluid and wave motions in the combustion system, driven by the gas ignition but influenced by many other factors. Recent progress has been made in our ability to model this portion of the combustion system [8]. A third key part of the overall combustor performance is the chemical process of reignition. Clearly the reignition and subsequent burnup of the fuel-air mixture must be complete within some fraction of the total cycle time, or combustion would proceed out into the exhaust system, which is not observed. The very fact that pressure oscillations occur is a further indication that the heat release must be complete within a rather small |
