Oscillatory fuel droplet vaporization: Driving mechanism for combustion instability

Liquid fuels are commonly used in the propulsion of ramjets and rockets, They offer great flexibility in terms of controlling the rate of energy release. However, combustion instability has historically been a major problem in the development of liquid fueled ramjets and rockets, Previous investigations that employed a simplified droplet vaporization model indicated that droplet vaporization is indeed capable of driving an instability. In this study, an established droplet vaporization model has been used to make an exact evaluation of the effects of pressure and velocity oscillations on the vaporization process of a droplet moving through a longitudinal mode standing wave in a combustion chamber. It Is then determined whether droplet vaporization as the burning rate controlling factor is capable of driving combustion instability. In addition, a parametric study has been conducted by using various frequencies of oscillation and amplitudes of fluctuation for the longitudinal mode. Depending on the local relative velocity between the gas and the droplet, it is possible that the wake may be ahead or behind the droplet, with reference to the chamber, This orientation has also been examined in the parametric study, It has been found that droplet vaporization is indeed capable of driving instability in some frequency domains and configurations. Preliminary results show that the amplitude of the oscillation does not have very significant effects on the response factor of the system, Orientation of the relative velocity, frequency of oscillation, and fuel volatility have strong influences on the instability.