Miniature-scale liquid-fuel-film combustor

Abstract

A new concept is explained for the miniaturization of cylindrical direct-injection liquid-fueled combustors wherein the fuel is flowed in a wall film that reduces heat losses, optimizes vaporization rate, and inhibits quenching. A simple analysis indicates that if a combustor of this type were part of a miniature engine, power levels from 10 W to 10 kW would be achievable with combustor volumes varying from a few hundred cubic millimeters to a few cubic centimeters and fuel flow rates varying from about 1 mg/s to 1 g/s. The combustor takes advantage of the fact that a surface area advantage of film combustion over spray combustion occurs for small volumes as the surface-to-volume ratio of the combustor increases. In addition, the wall film of fuel prevents heat losses while cooling the combustor surfaces. Photographs of a laboratory demonstration of the miniature film combustor concept with methanol and hepatane fuel and a mechanically swirled airflow are presented. The methanol flame required some methane gaseous fuel for stability, but the heptane fuel burned successfully alone. The experiments demonstrated externally and internally anchored flame modes, and a transition between them. The stability of internal burning was affected by internal fluid, dynamics and film dryout.