• Energy Research

Abstract Porous media burners (PMBs) enable enhanced combustion performance by internally recirculating heat released from the combustion products upstream to the reactants via an inert solid matrix. Compared to conventional free-flame systems, PMBs are characterized by higher burning velocities, extended flammability, and lower emissions of NOx. Current PMB implementations utilize a two-zone concept in which the flame stabilizes at the interface between two porous matrices of different topologies. In this work, a PMB design having a spatially graded porous matrix is proposed, supported by theoretical analysis of the governing equations and constitutive relations. Through computations and experiments, it is shown that the proposed physical design of the porous matrix results in a significant enhancement of the power-dynamic range and in excess of 50% higher blow-off limits compared to current designs. This is achieved through gradation in topology (i.e. porosity, pore diameter, cell diameter, etc.), which enables a continuous variation of radiative extinction properties as well as interphase heat exchange, allowing the flame to stabilize dynamically within the porous matrix and for a wider range of operating conditions.

Abstract In aircraft propulsion as well as stationary power generation, gas turbine engines remain a key energy conversion technology due to their high thermal efficiencies and low emissions. However, as emission requirements become increasingly stringent, engine manufacturers have sought to design combustion systems that operate near the fuel-lean limit of flammability. In this study, superadiabatic matrix-stabilized combustion, also known as porous media combustion, is evaluated as an advanced combustion concept for extending the lean flammability limit to achieve improved efficiency and emissions. To this end, a Brayton cycle analysis is developed and key parameters of the porous matrix are identified for maximizing the extension of the lean flammability limit. It is shown that stabilization of combustion below the nominal lean flammability limit allows for the design of engines with significantly higher pressure ratios and lower dilution ratios without increasing turbine inlet temperatures, thus improving cycle thermal efficiency. Combustor flammability limits were shown to be extendable by up to 32% when employing matrix-stabilized combustion, resulting in thermal efficiency gains of up to 11% compared to a nominal design.