Gaseous-Propellant Microthrusters. II. Venting Prior to Completion of Burn

Abstract

We present results from an inviscid one-dimensional model of the quasi-steady adiabatic dame propagation within a closed cylindrical container, as a consequence of a localized ignition in an initially homogeneous and quiescent mixture of reactive ideal gases. We continue the description after the instantaneous removal of an effectively massless diaphragm permits discharge from a sonic orifice, located at either the ignition end or the opposite end of the container. In a companion study (part I, published separately), the efflux begins only after the burn of the contents is complete; here, in contrast, the diaphragm is instantaneously removed when a pressure is achieved which is less than the adiabatic pressure for complete combustion of the contents. Key results include the temporal histories of the fraction of the initial mass that is burned within the container, the fraction of the initial mass that has exited the container, and the flux of momentum associated with the efflux of mass (for the case in which the container itself does not move). For cases of interest, involving a single simple hydrocarbon vapor in a fuel-lean mixture with oxygen and a diluent, at an initial pressure in excess of one atmosphere, the pressure increases mono-tonically (and appreciably) until diaphragm rupture; thereafter, the pressure typically decreases with efflux, and the flame speed across the mixture typically increases with the decreasing pressure. Thus, flameout (so the combustion within the container of the initial contents is incomplete) is neither coincident with diaphragm rupture nor owing to a chemical-kinetic consequence of the decrease of the (spatially virtually uniform) pressure. Rather, flameout is owing to the efflux of all hot burned gas from the container, so there is no preheating of residual cold unburned mixture to sustain propagation of the deflagration within the container.

Keywords:

• Automotive-airbag inflation
• auxiliary rockets
• gaseous-propellant rocket motors
• microthrusters
• minirockets

Additional information

Notes on contributors

F. E. FENDELL

Corresponding author, e-mail: [email protected]