Numerical and experimental investigation of synthetic biogas pulse combustion

Abstract

The pulse combustion propagation of a synthetic biogas mixture was numerically and experimentally studied. The gaseous fuel used in this study was a mixture of natural gas with 97% methane and CO2. Three equivalence ratios; 0.75 (lean), 1 (stochiometric) and 1.2 (rich) were used in the experiments. An experimental setup that consists of a stainless steel pulse detonation tube with 100mm inner diameter and 1700mm length, ignition control system and filling station was installed to measure the characteristics of pulse combustion such as pressure and velocity. The effect of different equivalence ratio and different percentage of dilution on the performance of pulse combustion detonation was investigated by using Chapman-Jouguet theory. Two modes of pulse combustion propagation wave were observed: deflagration, detonation and in some cases deflagration to detonation transition (DDT). Results showed that the sensitivity of the mixture toward the detonation decreased with the increase of carbon dioxide dilution and increased with the increment of the equivalence ratio. In this study, for the mixture with 50% dilution, DDT and high speed deflagration with the velocity of around 700m/s were observed. The results were compared with calculated data using Chemical Equilibrium with Application (CEA) code and it was considered that CEA is useful software for calculating Chapman-Jougeut detonation parameters such as detonation velocity and pressure. From the analysis of detonation cell width in the soot foil technique, it was observed that the stochiometric mixture produces bigger cell width compared to rich mixture. So this indicates that the detonation wave of rich mixture can propagate through a smaller tube compared to lean and stochiometric mixtures.