An experimental investigation into enhancing pulsejet performance through inlet redesign

Abstract

The objective of this research was to enhance the performance of a small scale pulsejet through the introduction of diffusion to the inlet geometry. In order to achieve this goal, two different inlets were designed, constructed and tested. These two inlets were designed using the concepts of internal and external diffusion (diffuser and cowl configurations respectively). The performance of these inlets was evaluated relative to the baseline inlet. The baseline inlet was defined as the inlet configuration currently operated by hobbyists on their pulsejet engines. The pulsejet operates the most efficiently at static conditions and the performance characteristics for a static run do not correlate to a dynamic operation. In order to simulate a dynamic operation, the engine was tested in a moving flow of air. The experimental data consisted of combustion chamber pressure measurements, inlet pressure measurements and thrust measurements. The diffuser configuration successfully achieved the research objective. The diffuser inlet was designed with the concept of internal diffusion and elevated the static pressure at the rear of the inlet. The increased static pressure facilitated the delivery of a larger air/fuel charge to the combustion chamber during each combustion cycle. This larger air/fuel mass was responsible for the higher peak combustion chamber pressure. Since the operational tests were conducted at a relatively constant cycle frequency, the higher peak combustion pressure produced more thrust for the pulsejet engine with the diffuser configuration. The cowl configuration was unsuccessful in achieving the research objective. The thrust and peak combustion chamber pressure results were the lowest for the pulsejet with the cowl inlet. These poor results were attributed to the air supply system. The air supply system was a simple free jet of air, thus could not provide a large cross-sectional area of uniform, steady flow. During engine operation, the large entrance for the cowl was ingesting a substantial amount of turbulent air. The consequences of this turbulent air were observed experimentally. Reed valve failure was more frequent and the pulsejet engine never ran smoothly with the cowl configuration.