Experimental and theoretical studies of laminar burning speed and flame instability of alternative fuels and refrigerants

Abstract

Alternative fuels and alternative refrigerants have attracted a lot of attention as many are deemed to be environmentally friendly. Consequently, the combustion behavior of fuels such as Syngas, Biogas, Liquified petroleum gas (LPG), and Gas to liquid (GTL) premixed flames were studied. In this investigation, the laminar burning speed and the flame instability of alternative fuels and refrigerants and different diluents (Exhaust gas recirculation (EGR), Helium, CO2) mixtures were evaluated both experimentally and numerically. Experiments were conducted using a spherical vessel to measure laminar burning speed and a cylindrical vessel to investigate flame instability. The cylindrical vessel is set up in a Z-shape Schlieren system, coupled with a high-speed CMOS camera that is used to capture evolutionary behavior of flames at up to 40,000 frames per second (around 2000 frames per second in general case). Upon ignition, the pressure rises as a function of time, during flame propagation in the spherical chamber, is the primary input of a multi-shell thermodynamic model, used to calculate the laminar burning speed for smooth flames. Power law correlations were developed for experimental burning speed results of different combustible mixtures over a wide range of equivalence ratios, temperatures, pressures, and diluent concentrations. For the onset of flame instability, a correlation for the ratio of critical pressure to initial pressure of syngas/air/diluent flames over a wide range of initial temperatures, initial pressures, equivalence ratios, diluent concentrations, and hydrogen percentages were developed. Kinetics simulations calculated by 1-D steady state flame code from CANTERA were compared with various experimental burning speed results--Author's abstract