We designed a reverse flow burner adopting a rapid mixing nozzle, which enables us to create high-preheat premixed flames. Lean limit of global flame quenching and flame characteristics of turbulent premixed flames formed on this burner were investigated changing preheat temperature, oxygen and fuel concentrations. As a result, the lean limit of global flame quenching extended to extremely low oxygen and fuel concentration conditions with an increase in preheat temperature, and we successfully formed the flame with extremely low density ratio of 1.15 between burnt gas and unburned mixture, hence mild heat release rate. OH-LIPF and temperature measurements showed that the turbulent flames formed with lean and diluted mixture have unique characteristics, such as (1) low mean and fluctuating temperatures, (2) non-continuous and well-stirred like OH distribution, (3) weak optical and sound emissions.
A combustion model for the multi fuel system was proposed based on author's previous model. Recently, customer requirement for dual fuel combustor of gas turbine is increasing. To simulate a combustion phenomena at the switching of fuels, the combustor model which includes the chemical reaction of mixing fuels is required. On the 1st and 2nd report, a united combustion model which is applied to premixed and diffusion flames [1,2] was proposed. The present model is natural expansion of the previous model. As the model includes the laminar flame speed Su and thickness of flame δ, the database of Su and δ on the multi component fuel was built due to CHEMKIN results. Especially, the database was estimated to the CH4-C3H8 fuel systems.
Oxidation characteristics of molecular hydrogen mixed with oxygen diluted with argon (H2/O2/Ar) in an intermittent dielectric barrier discharge (DBD) are investigated to remove hydrogen in an off-gas from fuel cell vehicles. The DBD reactor has coaxial electrode geometry and quartz glass tubes as a dielectric material. The discharge is formed the gap volume between electrodes at an applied peak-to-peak voltage of 31 kV at an atmospheric pressure. It is found that the gas temperature, the equivalence ratio, the gas residence time and the repetition rate corresponding to an energy density contributed strongly to hydrogen oxidation. A 100% hydrogen conversion is obtained at the energy density of 4.4 J/cm3 at the exhaust gas temperature of 80 °C under the equivalence ratio of 0.05. The oxidation mechanism of hydrogen is discussed using gas kinetics with 19 elementary reactions. When using the DBD plasma, the results show that the O- and H-radicals are the most influencing species for hydrogen oxidation in the direct treatment. The temperature effect is also discussed using the same computational method. It is pointed out that more reaction mechanisms and thermal effects in the DBD zone should be incorporated into the analytical technique.
This study investigated the characteristics of an unsteady lifted flame resulting from an instant change in the concentration difference through comparisons with those of a steady lifted flame to change from a premixed flame to a triple flame with a diffusion trailing flame identified in the middle. The instant change was done by an equivalence ratio conversion system using a solenoid valve and the flame photographs taken by an ICCD camera, were used for data extraction from the two lifted flames. The unsteady lifted flame stayed at for 1.6 seconds only and was classified into three regions, a premixed flame region, a critical flame region, and a triple flame region according to the gradients of the flames' curvature radius, width, lift-off height, and luminescence intensity as done in the steady lifted flame. The result was that the unsteady lifted flame made under a specific condition in this paper, showed a similar tendency in the gradients to the steady lifted flame. That is to say, the behavior of the unsteady lifted flame can be predicted based on the behavior of a steady lifted flame.
Deflagration-to-detonation transition (DDT) of methane-acetylene-air and propane-acetylene-air mixtures was experimentally studied to extend availability of pulse detonation engines using liquid fuels. The detonation tube has a total length of 7194 mm and an inner diameter of 50 mm. Volumetric percentage of acetylene in the mixed fuels ranged from 0 % to 100 % under the condition that total equivalence ratio was kept constant of 1.0. The experimental results show that increase in volumetric percentage of acetylene causes faster flame acceleration and earlier detonation transition. DDT was observed for the methane-based mixtures containing acetylene of more than 50 % in fuel and for the propane-based mixtures with acetylene of more than 20 %. Cell size of methane-acetylene-air mixtures and propane-acetylene-air mixtures increased with decrease in volumetric percentage of acetylene in the mixed fuel. Cell size of methane-acetylene-air mixtures was found to be proportional to the calculated reaction induction length in the case that volumetric percentage of acetylene was more than 60 %, whereas the ratio of the calculated reaction induction length to the cell size was dependent on volumetric percentage of acetylene for propane-acetylene-air mixtures.