Timothy Marbach

Experimental study of surface and interior combustion using composite porous inert media

Combustion using silicon carbide coated, carbon-carbon composite porous inert media (PIM) was investigated. Two combustion modes, surface and interior, depending upon the location of flame stabilization, were considered. Combustion performance was evaluated by measurements of pressure drop across the PIM, emissions of NO x and CO, and the lean blow-off limit. Data were obtained for the two combustion modes at identical conditions for a range of reactant flowrates, equivalence ratios, and pore sizes of the PIM. Results affirm PIM combustion as an effective method to extend the blow-off limit in lean premixed combustion.

INVESTIGATION OF A MINIATURE COMBUSTOR USING POROUS MEDIA SURFACE STABILIZED FLAME

Abstract In this study, heat recirculation in an annulus around the combustor is utilized together with the flame stabilized on the surface of a porous inert media (PIM) made of silicon-carbide coated carbon foam. The effectiveness of the proposed concept is demonstrated experimentally for methane combustion in chamber volume of 0.364 cm3 and overall system volume of 1.5 cm3. Experiments were conducted for reactant flow velocities varying from 0.25 to 1.0 m/s in the equivalence ratio range of 0.50 to 0.80. Measurements include carbon monoxide and nitric oxides concentrations and product gas temperatures at the combustor exit, and temperature profiles on the exterior surface. A computational fluid dynamics (CFD) model incorporating the physics of conjugate heat transfer, radiation heat transfer, flow and heat transfer in the PIM, and heat release by combustion is developed to predict the thermal performance. Results show excellent agreement between measured and computed temperature profiles at different reactant flow rates. The CFD analysis is used to identify important thermal pathways within the system. Finally, a modified design is presented and analyzed computationally. The modified combustion system design achieves a significant reduction in the heat loss as compared to the baseline design tested experimentally.

Heat-Recirculating Combustor Using Porous Inert Media for Mesoscale Applications

Small-scale power-generation systems offer an alternative to traditional batteries because of the high-energy density of hydrocarbon fuels. Combustion at small scales presents several challenges, including high heat loss and short flow residence times. Heat recirculation is an effective method to limit heat loss and improve combustion performance. However, new methods of achieving heat recirculation in a small volume must be developed for practical devices. To meet this requirement, a heat-recirculating, lean premixed combustion system using porous inert media (PIM) in the combustion chamber and in the preheating annulus around the combustor has been developed. System performance for a range of operating conditions was determined experimentally using methane fuel. Measurements include preheat and product gas temperatures and emissions of CO and NOx. Results show that the reactants were preheated in excess of 600 K by recirculating thermal energy from the reaction zone. Heat loss to the surroundings decreased and heat recirculation to the reactants increased with PIM in the annulus and with insulation of exterior surfaces of the system.

Fuel Vaporization and Combustion with the use of Porous Inert Media

Abstract The effect of vaporization/mixing length on the combustion performance of kerosene fuel using a SiC coated, C-C composite porous inert media was investigated. NOx and CO emissions data were obtained for combustion occurring on the surface and inside of the porous inert media. Increasing the vaporization/mixing length beyond a minimum value had no measurable effect on the combustion performance. However, as the vaporization/mixing length was decreased below a threshold, the CO emissions increased significantly. The increase was associated with poor fuel/air mixing, producing local hot spots in the combustion zone.

Optimization of a Mesoscale Combustor Using Heat Recirculation and Porous Inert Media

Continuous improvement of integrated circuitry has allowed for the development of small, sophisticated portable electronics and microelectromechanical systems (MEMS) for a wide range of applications. Compared to the electronics and other system components, the batteries powering small electronics and MEMS are large and heavy. Thus, smaller and lighter power systems are required to advance future products. Electricity for small systems may be supplied by miniature heat engines, which transform chemical energy of fuel into thermal energy, kinetic energy and electricity with the use of combustors, turbines and generators. Combustion at small scales is challenging because system heat losses to the surroundings are large and flow residence times are short. Heat recirculation can be used to improve combustion performance by reducing these heat losses and preheating reactants prior to ignition. Practical heat recirculation systems must be small to keep the overall system volume and mass small. The objectives of this study were: (a) to investigate heat transfer in miniature combustors, and (b) to identify effective means of reducing heat loss from small combustors. The analyses indicated that axial conduction through the combustor wall and radiation across the preheating annulus were the most significant pathways for heat loss from the system. Several design improvements, including extended surfaces and porous inert media (PIM) were analyzed. A design featuring PIM in the annulus with a gap between the PIM and outer wall was the most effective method of reducing system heat loss.Copyright