Pulse combustion studies of propane and natural gas mixtures

Abstract

The phenomenon of pulse combustion of hydrocarbon-oxygen mixtures was investigated experimentally. An experimental rig that consists of a stainless steel tube with inner diameter of 100mm and length of 1700mm, data acquisition system, ignition control unit and filling system was built in order to measure the characteristics of pulse combustion such as, pressure, velocity and impulse. Three equivalence ratios of fuel-oxidizer; 0.75, 1 and 1.25 were chosen to investigate the effect of fuel concentration on the pulse combustion wave propagation. It was found that combustion of high fuel concentration mixture propagates as a detonation wave while for low fuel concentration mixture; the combustion wave propagates as deflagration wave. Two types of hydrocarbon fuels were used, i.e, propane and natural gas with 92.7% methane. Results showed that natural gas is not sensitive to detonation propagation compared to propane. It was found that in smooth inner wall tube, combustion wave propagates as a detonation wave if the percent of dilution gas is not more than 35% and it is a function of the equivalence ratio. In order to accelerate the combustion wave into detonation wave within 0.5m of the tube, array of obstacles with identical blockage ratio was placed inside the tube, near to the ignition source. It was observed that the obstacle enhances the transition process within the given length. The ignition source was set at three energy levels, i.e., 25mJ, 5J and 100J. The chosen level of ignition energy did not affect the combustion wave propagation in a smooth inner wall tube but in a rough inner wall tube, it improved the generated impulse force. Impulse measurement using an accelerometer was made to measure the impulse produced by the combustion wave. Generally, the detonation wave produces larger impulse force as compared to deflagration wave.