Experimental and numerical investigation on diluted DME flames: Thermal and chemical kinetic effects on laminar flame speeds

摘要

Experiments and computational simulations were used to study effects of diluents on laminar flame speeds of stoichiometric, laminar, premixed dimethyl ether (DME)/air flames. The experiments were conducted in a constant volume bomb under initial temperature of 298 K and initial pressure of 0.1 MPa. Outwardly propagating spherical flames were used to measure the laminar flame speeds of mixtures with varying concentration of Ar, N_2 or CO_2 addition. Laminar flame speeds were also computed using the steady, one-dimensional laminar premixed flame code PREMIX with detailed chemical kinetics. Predictions showed a good agreement with experiments. For all the three diluting agents invested in this work, laminar flame speed decreases with the increase of dilution ratio, while for a given dilution ratio, the significance of suppression effect on laminar flame speed is in the order of CO_2, N_2 and Ar. The suppression effects of N_2 and Ar on flame propagation are mainly caused by reduced reactant concentration and modified heat capacity, both of which result in a decreased flame temperature, while besides that, CO_2 further influences the chemical kinetics because it is a major product of combustion. Further experimental study on flame speed and simulation study on flame structure at fixed adiabatic flame temperature were conducted to evidence this speculation and the possible reaction pathways which contribute to the chemical retarding effect by CO_2 addition were recognized through sensitivity analysis.