An investigation of the performance of a carbureted, liquid fuelled, valveless, pulsed combustor
Creators: name: Ibrahim, Gawdat Mohamed Saleh
Publisher: name: University of Calgary
Year: 1979
Subjects: subject: TJ 773 I35 1979 Microfiche
subject: Combustion research
subject: Gas flow
subject: Gas-turbines - Combustion

description: Bibliography: p. 143-149.
description: The report opens with a brief historical review of the development of pulsed combustors, from what appears to be the first report on pulsating combustion of about 1800 to contemporary evolution. This investigation examined, primarily by experimental means, methods of improving the performance of a liquid fuelled valveless pulsed combustor incorporating a carburetor. The carburetor was equipped with an automatic non-return valve to prevent inlet backflow. In order to lay the foundation for adequate design and development of the pulsed combustor, some parameters affecting the performance of the combustor were considered briefly. These included; analysis of the non-return valve, influence of the fuel head, the carburetor jet diameter, the temperature of the mixture, droplet size and evaporation, ignition delay and the pressure drop across air-intake. To generate information which would permit improvements to be made to the design of the fuel spraying system, steady flow, flow visualization tests, using water as a substitute for fuel, were carried out. Experiments with different spraying arrangements led to modification of the spraying system with consequent improvements in the performance of the pulsed combustor. To obtain yet further improvements, a lengthy experimental optimization process was conducted with the purpose of establishing the optimum geometry for the combustor consistent with the best achievable performance. Geometric parameters such as the configuration of the fuel nozzle, the size of a cone placed on the fuel nozzle, the size of the orifice restricting the carburetor inlet and the thickness of the combustor wall were investigated. Furthermore, the use of an air swirler and a regenerative intake air heater were explored. Based on the foregoing results, a modified air-intake was developed to reduce the pressure drop across the duct and consequently increase the forward thrust. The modified air-intake featured the use of a streamlined body designed to avoid separation of the boundary layer and to obtain a small drag. To eliminate the automatic non-return valve incorporated into the carburetor, a fluidic device was designed and manufactured. The fluidic carburetor combined, intimately, a vortex diode with an auxiliary-passage flow-rectifier. The influence on performance of the size of the vortex diode underwent experimental study. Coupling of two vortex diodes arranged in series was also investigated. To assess the versatility of operating on different liquid fuels, the pulsed combustor was tested using gasoline, iso-octane, n-heptane, kerosine and diesel fuels. Thrust was considered as the most important performance parameter as it is a measure of how effectively the combustor performs a pumping action. Fuel flow rate and specific fuel consumption were taken as the independent variables against which all the dependent data were presented. To study the performance variation with different fuel flow rates, the characteristics of the optimized combustor were established over its full operating range. The development of a liquid fuelled valveless pulsed combustor incorporating a carburetor along the lines described in the text was shown to appear to be a feasible proposition. It was demonstrated experimentally that the combustor produced, when operating on kerosine, a maximum total thrust of 1.23 lbf/in 2 (8480 N/m 2 ), at 3600 ft (1100 m) altitude, referred to the combustion zone cross-sectional area (corresponding to 3" (76 mm) diameter).