Physical and Chemical Processes Controlling Fuel Droplet Ignition

Abstract

*† The ignition delay for the incipient sustained reaction of hypergolic propellants is of crucial importance. Too short of a delay c an lead to injector damage while too long of a delay can lead to very large pressure spikes and engine failure. The coupling of the physical and chemical processes controlling the ignition delays of hypergolic propellants renders the direct analysis of th e transient ignition process very difficult. Well defined test conditions must therefore be specified to properly study the factors influencing the ignition delays of hypergolic propellants. Of particular interest is the influence of low pressure conditi ons upon ignition delays. Past studies have shown that both the vaporization process and the ignition process of high vapor pressure propellants are strongly altered with decreasing pressure as the role played by liquid -phase reactions is emphasized. The current study focuses on the effects of reduced ambient pressures for propellants with varying vapor pressures. Ignition models are reviewed and these effects are examined within the context of the accepted theory. The results of a series of ignition del ay experiments are used as a basis for the development of a proposed ignition model applicable to low vapor pressure propellants in reduced pressure environments.