Experimental And Numerical Study Of Premixed Superadiabatic Combustion In Porous Media With Reciprocating Flow

Superadiabatic combustion of premixed combustible gases in porous media with reciprocating flow (RSCP), which is known as one of the most advanced combustion technologies, possesses a number of advantages over conventional combustion technology. In this paper, experimental study, numerical simulation and theoretical analysis are carried out on the combustion and emission characteristics of RSCP. The main works are as follows:1. An experiment facility is set up, which consisted of a ceramic foam (A1₂O₃) combustor, a gas flow system controlled by two pairs of solenoid valves for switching alternatingly the flow directions, and a measurement system. The temperature distributions in porous ceramic combustor are measured by using thermocouples and an infrared radiation technique. Using a combustion efficiency analyzer, the measurements of CO and NO components in the exhaust gas of RSCP are carried out. The temperature distribution inside the porous medium combustor and the levels of NO and CO emissions are measured at various working parameters. Based on the experimental results, the working mechanisms of extending flammable limits and lower NO and CO emissions are discussed and the influences of the major parameters on the combustion and emission characteristics of RSCP are clarified.2. The temperature distributions in combustion chamber are considered one-dimensional. Both two-temperature model based on the local thermal non-equilibrium and one-temperature model based on the local thermal equilibrium between the solid and gas are established, and numerical calculations are fulfilled to simulate the temperature distribution in porous media at various working parameters. The calculation results are compared with the experiments. The cause for the discrepancies between calculations and experiments are discussed.3. Based on a simplified model, a theoretical analysis was carried out on the temperature distributions characteristics of RSCP system. A approximated solution for the temperature distribution in RSCP at finite half cycles is obtained by properly combining the theoretical solutions in the filtration combustion for two limit cases, i.e. reciprocating flows with infinite large and infinite small (zero) half cycles.The conclusions obtained by the experiment study, numerical simulation and theoretical analysis results are as follows:1. The periodic configuration of the temperature profile in the RSCP system is basically trapezoid shape with steep gradients at both inlet and outlet sides. During combustion process, reversing the flow direction at regular time interval, the catching fire occurs after the flame in last half cycle quenches, and the high-temperature plateau travels from the upstream side of the porous media towards the downstream as the half cycle goes on. The combustion is a periodic evolution process. At various working parameters, the periodic evolution processes show different characteristics; the double wave structures of the hot-spot structure can be observed under some conditions.2. The temperature distribution and the maximum temperature inside the porous medium combustor, the combustion efficiency and the levels of NO and CO emissions dependstrongly on the major parameters (gas flow velocity, fuel-air equivalence ratio and half cycle period). With increasing flow velocity, the maximum temperature markedly increases, the high temperature region widens, the combustion efficiency decreases, while the NO and the CO emissions increase. With increasing fuel-air equivalence ratio, the maximum temperature markedly increases, high temperature region widens, the combustion efficiency increases, and the NO emissions increase while the CO emissions decrease. With decreasing half cycle period, the maximum temperature slightly increases, high temperature region widens, the combustion efficiency increases, and the NO emissions increase while the CO emissions decrease. There is a qualitative agreement between numerical simulation and experiment results. The discrepancy is at...