Experimental and Theoretical Study of Combustion under Elevated Pressure within Porous Inert Media

Abstract

Gas combustion occurring within porous inert media (PIM) results in intensified heat and mass transfer in comparison to free laminar combustion. This leads to considerably lower emissions of pollutant species, that is, NOx and CO, larger flame stability range, lower thermo‐acoustic instabilities, gradual response to operative changes, and geometric flexibility of design. In this work, experiments were carried out to describe the influence of flow rate, pressure, temperature, and air‐to‐fuel ratio on the flame stability within PIM at nearly adiabatic conditions. The macroscopic thermal flame thickness and the burning velocity were calculated from measured temperature profiles and flow rates. As the main result, it was observed that the pressure effect on the burning velocity can differ considerably from that of laminar free flames, that is, the increase of pressure can positively affect the burning velocity. The obtained results were supported by theoretical modeling. A new model to average the species production rates in a volume‐averaged numerical model was proposed. The model considered spatial deviations of temperature and mass fractions along the cross‐sectional area using presumed probability density functions. Using this new model, results of burning velocities and profiles of average temperature were satisfactorily predicted when compared to experimental results shown here. Furthermore, easy‐to‐use tools for porous burner design were formulated and validated.

Experimental Characterization of a Novel Foam Burner Design for the Low-Excess-Enthalpy Combustion of Very Lean Syngas Mixtures

“…Accordingly, an estimation of the burning velocities for the given mixtures was performed. In the present work, a simplified engineering approach is utilized in order to calculate the burning velocity of the examined mixtures according to a semi-empirical correlation based on the work of Bedoya et al, 2017 [6]. The correlation is based on the similarity between the Peclet numbers of free flames and flames stabilized in an inert porous media (i.e., the ceramic foam).…”

“…Adiabatic laminar flame speeds for freely-propagating mixtures with the same composition as those used in the current campaign are calculated using the CHEMKIN suite of the ANSYS software [16] and the detailed kinetic mechanism proposed by Malliotakis et al [17]. The correlation in [6] is then used in order to obtain the corresponding burning velocities inside the foam burner. Volumetric flowrates are then derived, assuming that the flow velocity equals the burning velocity.…”

“…Further, a more homogeneous reaction zone is established with generally lower temperatures than the corresponding gas-phase flame. As a result, the flame stability is increased, and emissions are reduced [6,7]. Further, the low enthalpy rises and the homogeneous temperature field inside the burner results in very low NO x emissions.…”

Experimental study on the combustion of low‐calorific NG/N2 in a porous burner

“…The difficulty of utilizing such gases with conventional combustion technology means that they are often discharged directly to the environment, 3,4 resulting in a lot of energy wastage and environmental pollution 5 . Therefore, novel technologies, such as regenerative thermal oxidation (RTO), 6 exhaust gas recirculation (EGR), 7,8 and porous media combustion, 9‐11 have been developed to handle LCFGs. However, in both EGR and RTO, large volume regenerators are required to preheat the fresh air, and the corrosivity of exhaust gases is also a major problem for the former.…”

“…Therefore, novel technologies, such as regenerative thermal oxidation (RTO), 6 exhaust gas recirculation (EGR), 7,8 and porous media combustion, [9][10][11] have been developed to handle LCFGs. However, in both EGR and RTO, large volume regenerators are required to preheat the fresh air, and the corrosivity of exhaust gases is also a major problem for the former.…”