The objective of this paper is to discuss the practical needs and research challenges in representing electrochemical processes in fuel cells, especially solid-oxide fuel cells. Most present-day fuel-cell modeling relies on significant approximations such as equilibrium chemistry or single-step global chemical kinetics. Charge transfer is usually handled in a Butler-Volmer setting, assuming a single rate-limiting step. This paper discusses elementary approaches to thermal and charge-transfer chemistry and their interactions. It also discusses approaches for coupling elementary chemistry with fluid flow and porous-media transport.
Instantaneous, 2-D-sliced flame visualization scheme based on acetone-OH simultaneous PLIF (Planar Laser-Induced Fluorescence) concept is proposed and its applicability to flame diagnostics on premixed combustion is addressed. Acetone seeded in the fuel flow and flame-generated OH are visualized simultaneously via PLIF with one line (which corresponds to OH Q1(7) (1,0) band absorption line: 283.2 nm) and fluorescence signals from acetone/OH are corrected by one detector; thus only conventional PLIF set (one laser and one detector combination) is required. In the present system, acetone and OH act as marker of unburned and burned zone, respectively. Qualitative behaviors of "no-signal zone (dark zone)" formed between these fluorescence signals are examined in methane-air flames (both laminar and turbulent conditions). Results show that the thickness of the dark zone varies depending on the equivalence ratio and the flame thickness experimentally defined as fuel 50 % -OH 50 % distance is well correlated to corresponding theoretical results (distance from starting point of preheated zone to heat release zone) in wide range of mixture conditions, indicating the validity of the present-proposed visualization scheme. Distinct dark zone can be clearly observed even in turbulentcases and some images show unburned 'island' flame structures, suggesting the applicability of this scheme to the complex turbulent combustion diagnostics. Under the condition of unity Le (Lewis number), this scheme may show thethree-dimensional flame configuration through the difference of the dark zone thickness. Advantage and disadvantage of the present-proposed scheme are addressed and milestones for further study are pointed.
Burned gas properties of the rapidly mixed type combustion in a tubular flame burner have been experimentally investigated. Results show that the flammable range for the rapidly mixed type combustion is almost the same as that for premixed type combustion except that the rich limit is slightly narrowed, the burned gas compositions and temperature at the burner exit are also almost the same as those of the premixed type combustion, while the NOx emission are 10-15 % less than that of premixed type combustion for lean and the stoichiometric mixtures. These results demonstrate the potentialities of the rapidly mixed type combustion in a tubular flame burner, which is free from flame flash-back accident.
The effects of the low air-ratio combustion on a waste incineration process have a reputation for reducing environmental pollutants such as dioxins or nitric oxides and improving the waste heat recovery. However, it was difficult to incinerate appropriately under a low excess air condition due to the combustion instability caused by heterogeneity of waste materials. Although the High-temperature air combustion technology opened the way for the realization of stable low air-ratio combustion at a stoichiometry of 1.3, it required amount of fuel for heating the high-temperature mixed gas -that is controlled oxygen concentration and preheated- up to 400°C which is injected above the fuel bed of the furnace specifically. From the point of view of the energy-saving issue, it is desirable to minimize the fuel consumption. A practical low air-ratio combustion test is conducted on an actual MSW incineration plant 105 tons per day capacity with the temperature of the high-temperature mixed gas up to 250°C that can be increased by using waste energy recovery system yields the same result as the 400°C condition. Therefore, the low air-ratio combustion can be achieved in a stoker-typed incinerator system without using an external energy. Also it deemed to have a relation between the toxic product emission and primary combustion process.