Experiments on the effect of exhaust gas recirculation diluent on the laminar burning speed and stability of syngas/air flames

Abstract

The laminar burning speed is one of the most important intrinsic properties of a combustible mixture that adequately characterizes a fuel. It is important to understand the laminar burning speed's dependence on various parameters such as the fuel, pressure and temperature, fuel/oxidizer equivalence ratio and diluent. The laminar burning speed of synthetic gas (syngas), which is a gaseous mixture of H2 and CO, that is diluted with inert exhaust gas recirculation (EGR) is presented in this thesis as well as a study of flame stability. Experiments were performed in a spherical chamber and a cylindrical chamber. The cylindrical chamber is installed in a Schlieren/shadowgraph setup that captures the density variations of a propagating flame using a high-speed CMOS camera, which are used to track any deviations from a smooth, spherical, and laminar flame, such as cellularity or buoyancy. The combustible mixture is centrally ignited in the vessel using extended spark plugs and the pressure rise resulting from combustion is recorded by a pressure transducer fitted to the wall of the chamber, which is the primary input to the thermodynamic model used to calculate the laminar burning speed. The conditions presented in this work are for 5:95, 10:90, and 25:75 H₂ to CO fuel ratios, over equivalence ratios that ranged from 0.6 to 3.0, pressures of 0.5-3 atm, and temperaures of 298-400K, which were diluted by 5% and 10% EGR that has a composition of 14% CO₂ and 86% N₂. A power law correlation is presented for the laminar burning speeds of H₂/CO/air/EDG.