Experimental investigation of lean premixed pre-vaporized liquid-fuel combustion in porous media burners at elevated pressures up to 20 bar

Abstract

Combustion in porous media has been identified as a promising technology for achieving higher burning rates, extending flammability limits, and reducing emissions. To assess the viability of this technology for application to aviation gas-turbine engines, the performance of a Porous Media Burner (PMB) operated with pre-vaporized liquid fuel at high pressures is experimentally examined. The PMB was operated at fuel-lean equivalence ratios between 0.4 and 0.55 at pressures up to 20 bar with fully pre-vaporized and preheated n-heptane as well as gaseous methane at 8 bar for performance comparison. Combustion stability maps are reported along with temperature profiles, pressure drops, and emissions of CO and NOx at stable operating conditions. Results from these experiments show excellent performance of PMBs at high-pressure conditions. Additionally, numerical simulations using the volume-averaged, one-dimensional reacting flow-equations complement the experimental measurements to provide further insight into the effects of the pressure and fuel mixture on the flame structure. Lastly, high-resolution es X-ray Computed Tomography (XCT) is used to examine the structural integrity of the porous matrix during the high-pressure combustion operation, showing evidence of micro-fissures and an increase in the surface roughness due to SiC-oxidation. Large-scale defects were not observed after four days of cyclic high-pressure testing over a wide range of pressures, heating rates, and equivalence ratios.