For the purpose of establishing reduced kinetic mechanism applicable to high-temperature air combustion technology (HiCOT), numerical simulations of the methane-air diffusion flame were performed especially at air temperature of 1300 K and low oxygen concentration of 4 vol %. First, numerical simulations for the one-dimensional counterflow diffusion flame were performed to find suitable reduced kinetic mechanism for HiCOT. Based on the comparison of the numerical results and improvements of steady-state expressions, improved Peters 4-step reduced mechanism (IP4M) was chosen. Secondly, numerical simulations for axisymmetric jet diffusion flame were performed mainly using the IP4M. Because of the numerical instability for the reduced kinetic mechanism peculiar to calculations of multi-dimensional problems, the rapid increase in H radical in non-reacting regions was found. It was also found that certain distinctions between the reaction region and the other region and restrictions of some elemental reactions were better way to overcome the numerical instability. Finally, converged solutions could be obtained and the results using IP4M agreed well with those using the starting full chemistry. Cost of calculation was also compared and it was shown that CPU time using IP4M was about one-third compared to that using the starting full chemistry.
In this study, we have numerically investigated flame spread over solid fuel in partially premixed atmospheres, which may occur under poorly ventilated conditions, forming the combustible mixtures of oxygen and fuel vapors. For simplicity, only gas phase is considered to simulate the flame spread, by moving the area of fuel injection at the solid surface. To confirm the validity of our numerical model, we have experimentally examined a non-premixed flame in the laminar boundary layer over a porous flat plate, from the surface of which fuel gas is injected uniformly. The plate of fuel injection is placed parallel to the ambient air flow. Methane is added in this ambient air to form the partially premixed mixture. Temperature measurement has been conducted. Results show that, the flame structure over the porous flat plate is well simulated, although the flame temperature is much overpredicted. In partially premixed atmospheres, the flame spread rate is increased, with the expanded high temperature region. This is because the fuel already exits in the upstream region to support the flame propagation. These results are very similar to our previous experiments using filter paper sheet as solid fuel.
A high emphasis is placed on disposal of waste gas from various plants because of rise of environmental consciousness. A catalytic combustion deodorizer that has an advantage of low running cost is getting a lot of attention. Honeycomb is commonly used for catalytic combustion deodorizer. But, the measurement of temperature and concentration in the honeycomb is very difficult, because honeycomb is assembled with a lot of millimeter-sized channels. So, it is necessary to investigate the physical quantity by the numerical simulation and to understand the phenomenon in the honeycomb. This paper describes the results obtained by the numerical simulation for catalytic combustion of CH4/air mixtures on palladium catalyst in honeycomb used in deodorizer. The numerical model has the elementary reaction kinetics considering nine surface chemical species. The details of catalytic combustion in a channel, such as temperature and mole fraction in the gas phase, surface temperature, heat release rate and coverage at the catalyst, are obtained. Especially, the effects of inlet conditions such as inlet velocity, inlet temperature and fuel equivalence ratio on characteristics of catalytic combustion are examined, and the catalytic reaction mechanisms are made clear.