The concept that the combustion is the chemically reacting gaseous flow has successfully been applied in the development of laminar flame theory. The accompanied reaction provides two important distinctions to be noticed in the flow behavior. First of all, the effect of heat release is so predominant that the flow becomes quite different from the flow without reactions. Secondly, the nonlinear response of reaction rate to the temperature increase plays a crucial role in the laminar flame behavior, leading to the emergence of multiple steady state solutions. The origin of this unique characteristics is the Arrhenius rate expression. In the present description, the approximate method to apply to this expression is introduced and explained.
Reminiscences of the activation energy asymptotic analysis developed and used to explain combustion phenomena theoretically are presented. The difference between theory and numerics, and the characteristics of the asymptotic analysis are described along with the history of the analysis and the spirits of theoreticians.
Several small talks on combustion I encountered in my career are introduced. These are solid propellant research, an instability problem on cellular H2 flames, flame extinction by powder, an asymptotic solution on plasma jet igniter, my sexual harassment with CHEMKIN code, an accident in a super sonic engine wind tunnel (RJTF), flame structure found in scramjet combustor and thermal choking encountered in engine tests, et al. I enjoyed these studies during my healthy, bright days. These days passing-by are always beautiful. The driving force stimulated my combustion research is my trivia accumulated in my younger ages.
Explosions of reactor buildings were recorded by a TV crew monitoring Fukushima-Daiichi Nuclear Power Plant after the large earth quake on March 11, 2011. Two series of images are analyzed with image processing. X-t diagrams constructed from these images are used to estimate the velocities of moving objects. The spatial length are determined from the heights of buildings in these images. The time interval of images is also determined from the video frame rate. Based on the obtained velocities, the flame propagation velocities, decompression wave velocity, and fragment initial velocities are estimated. The overpressures of two explosions are estimated based on the fragment initial velocities. The obtained flame propagation velocities are lower than the speed of sound. The estimated overpressures are 27 kPa for Unit 1, and 149 kPa and 193 kPa for Unit 3.
The present study aims to clarify the mechanism of cellular pattern formation on soot foil records in gaseous detonation propagation by applying other materials and to find alternative tools for visualization of the cellular structure. The experimental results show that the magnified images around the lighter soot track by SEM and EPMA well demonstrate local removal of soot deposit along the trajectory of the triple points. In addition, it is possible to obtain cellular patterns using CaCO3 particles, fly ash, and heat sensitive paper, instead of soot particles coated on metal foils, while applying Al2O3 particles gives no characteristic pattern. The symmetrical cellular pattern with the soot foil record is shown for CaCO3 particles and fly ash, which suggests that hydrodynamic effects are responsible for cellular pattern formation because of nonflammability of these particles. The quantitative estimation of sheer stress and tensile strength of agglomerated particles explains the critical particle diameter required for particle detachment, although the sheer stress is not strong enough for particle removal in cellular pattern formation. As for the heat sensitive paper, it is deduced that relatively large amount of heat is transferred to the paper near the trajectory of the triple points. The present results indicate that the soot foil technique is superior to the other methods in recording the cellular structure under wide variety of experimental conditions.
The effects of flame curvature on the fuel consumption rate has been studied by means of 2-D numerical calculation with detailed chemical kinetics and accurate transport properties for a rich hydrogen-air mixture. It has been found that the local fuel consumption rate increases at the low-temperature side of flame portion where the flame develops curvature. The full use of the numerical data has been made to understand the cause of this increase. It has been found that the supply rate of H by molecular diffusion to the reaction zone is accelerated, which eventually produces the increase in OH concentration leading to this increase. The same trend of increase of fuel consumption rate with the flame curvature has been observed in the detailed 3-D simulation of a hydrogen jet lifted flame, and then the mechanism discussed in this study is one of the key mechanisms to understand the structures of turbulent premixed flames.
Pulsed Flame Jet (PFJ) ignition system has a great potential to improve ignition reliability of lean fuel/air mixtures. The PFJ igniter used here has the same size as conventional spark plugs equipped with a small cavity of 170 mm3 in volume and an orifice of 2.5 mm in diameter. A rich methane/air mixture was introduced into the cavity and it was ignited by a spark discharge. In this paper, the orifice was opened into the air of an atmospheric pressure and a room temperature to obtain the pure characteristics of the jet with varying the spark discharge mode in the cavity of the PFJ igniter. Four different spark discharge modes in the cavity were used. Actions of OH radicals in the jet were captured based on the Planar Laser Induced Fluorescence (PLIF) technique, and temporal variations of OH fluorescence area, its mean intensity, and total intensity were evaluated from the images of OH fluorescence. Then the effects of spark discharge modes on the production of active radicals such as OH in the PFJ were revealed.