Mitsuhiro Tsue

Observation of sooting behavior in an emulsion droplet flame by planar laser light scattering in microgravity

Two-dimensional visualization of the soot concentration profile in a flame formed around a suspended droplet was carried out under microgravity conditions using the planar laser light scattering technique. The 500-in drop shaft in Japan was used for microgravity experiments, which offers the effective time of the microgravity of 10 s and the relatively large space of the falling assembly for constructing the optical measurement system. The soot concentration and the instantaneous amount of soot were estimated approximately from the intensity of the scattered light using the image analysis system. The fuels employed were water-in-oil emulsions composed of base fuel, water, and surfactant. The base fuel was n -dodecane. The sooting region can be observed spherically around the droplet by using the apparatus developed in the present work. The results showed the unsteadiness of the sooting behavior and the flame behavior. Most of the soot concentration is located in the vicinity of the inner edge of the sooting region, which corresponds to the soot shell observed previously. The maximum of soot concentration does not vary with the water content, whereas the maximum amount of soot decreases significantly with water emulsification.

Statistical analysis of onset of microexplosion for an emulsion droplet

A experimental study has been carried out on the burning behavior of an emulsion droplet suspended on a quartz fiber. Attention was paid mainly to the coccurrence of microexplosion, which may be caused by the bubble nucleation at temperatures below the superheat limit. The oil-in-water emulsion consisting of the base fuel and water was employed after degasification. The base fuels used were n -tetradecane and n -hevadecane. The water content varied from 0.1 to 0.3 by volume. The waiting time for the onset of microexplosion was measured for about 30 runs. The microexplosion is assumed to be a random process, and the onset probability of microexplosion was discussed from the statistical point of view. The Weibull distribution, which is derived mathematically from the weakest link destruction model, was adopted for this purpose. The results showed that the distribution function of the waiting time correlated with the Weibull distribution. The distribution function is classified the wearout type at the initial heating period and as the chance failure type at the constant-temperature period. Thus, the type of Weibull distribution of the waiting time is dependent on the variation of the droplet temperature with time. The onset rate of microexplosion increases exponentially as the superheating of water increases. The reliance of the onset rate on the superheating of water is independent of the base fuel.

Numerical Analysis on Flame Kernel in Spark Ignition Methane/Air Mixtures

A flame kernel initiation of methane/air combustible mixtures in the spark ignition process was investigated using a two-dimensional theoretical model including a detailed description of gas-phase chemical kinetics, shock capturing scheme and diffusive molecular transport. Interactions of chemical reactions and diffusive transports of radicals in the process of the flame kernel initiation were investigated. Although the model of plasma might be oversimplified, the qualitative behavior of OH for hydrogen/air mixture agreed well with experimental one. The influences of diffusive molecular transport and ignition energy on the flame kernel initiation were discussed. As a result, in the early stage of the flame kernel development for methane/air mixture, the hot gas expansion was dominated by a flow whichwas inducedby the blastwave and the thermal gas at the electrode gapwas self-sustainedwith anapplication of minimum ignition energy. The induction time of the flame kernel initiation strongly depended on the ignition energy and effects of preferential diffusion of lighter molecules in the early phase of the flame kernel development are outstanding especially in the case of low ignition energy near the minimum.

Optical Measurements of Ethanol/Liquid Oxygen Rocket Engine Combustor with Planar Pintle Injector

The pintle injector is a promising candidate of the propellant injection systems for a rocket engine with deep throttling capability which is essential for future space transportation missions. However, studies focusing on combustion phenomena in a rocket engine with a pintle injector is rather limited. In this study, optical measurements inside an ethanol/liquid oxygen rocket engine combustor with a planar pintle injector are conducted to clarify spray and flame structures in the pintle injector. Combustion tests where the chamber pressure is 0.36 to 0.40MPa and O/F is 1.15 to 1.40 are conducted. Effects of the injection configuration on spray structures are also evaluated. High speed imaging techniques are used to observe the flame and spray structures under hot fire conditions. Strong chemiluminescence of CH is observed in the vicinity of the impinging point of two propellants. Luminous flame is observed intermittently in the vicinity of the faceplate and the upper wall of the combustor with the direct observation of the flame. Characteristic exhaust velocity efficiency with oxidizercentered configuration is lower than fuel-centered configuration due to the large amount of propellant impinging on the upper wall of the combustor. Periodical phenomena with the frequency of approximately 300Hz which can be related to atomization processes are also observed.