High-pressure turbulent premixed combustion of biofuels

High-pressure turbulent premixed combustion of the second generation biofuels, i.e., propanol and butanol were experimentally investigated at pressures up to 1.0 MPa. Observations of instantaneous flame structures of Bunsen-type turbulent premixed flames for the fuels were performed using OH-PLIF. The local flame surface density profiles were measured to explore the effects of isomers on flame structure in terms of intrinsic flame instability in turbulent premixed flames for weak turbulence. Numerical analysis of flame instability based a two-step reaction model simulating fuel dissociation reaction in diffusive-convective region, which is a significant feature of fuel isomers, was also performed. The flame surface densities for 2-propanol and iso-butanol flames were greater than those of 1-propanol and 1-butanol flames, indicating that the intrinsic flame instability for high pressure turbulent premixed flames initiated by weak turbulence was enhanced, although thermal properties of the isomers are almost identical. A new mechanism to enhance or restrain flame instability caused by Lewis numbers and chemical enthalpy of intermediate species was presented based on the results of numerical analysis and comparisons with experimental results. Those finding can be used not only for understanding turbulent combustion phenomena in practical combustors for biofuels but also fundamental research of turbulent flame dynamics in a high-pressure environment.