Shunichi Ohigashi

Bio: Shunichi Ohigashi is an academic researcher from Kyoto University. The author has contributed to research in topics: Flow velocity & Combustion. The author has an hindex of 7, co-authored 10 publications receiving 106 citations.

Effects of Turbulence on Flame Propagation in Closed Vessel

Abstract: The effects of turbulence on the flame propagation in the propane-air mixture in a closed vessel were investigated by analyzing the high speed motion pictures of flame, the ion-currents due to combustion and the change of the gas compositions in combustion zone. In the combustion chamber, the uniform turbulent conditions were produced by moving suddenly a perforated plate which was driven by the spring and the electro-magnetic control system. The main results are as follows: (1) The combustion zone of turbulent flame may be composed of a lot of flame elements which are similar to laminar flame, and the apparent burning velocity is increased by enlargement of combustion zone due to turbulence. (2) during the early stage following ignition, the flame speed is affected by both factors of mixture strength and intensity of turbulence. with further development of the flame, however, the intensity of turbulence becomes a dominant factor determining thee flame speed.

Vaporization and Combustion of Single Liquid Fuel Droplets in a Turbulent Environment

Abstract: Vaporization and combustion processes of liquid fuel droplets in a fluctuating turbulent gas environment without any time-mean flow velocity are investigated. Such environment simulates adequately the flow field where average flow velocity is nearly equal to the droplet particle velocity. This paper also deals with the methods and instruments used in measuring turbulence quantities such as intensity and scale in this turbulent environment. Steady state empirical equations of heat and mass transfer for liquid sphere are applicable accurately to the evaporation of droplets under the condition of quasi-steady state in this turbulent environment. On the other hand, combustion in the turbulent environment is not like that under the forced convection and the flame shape is not tailed but almost spherico-symmetrical with wrinkled edges. The burning rate increases proportionately with eddy diffusivity and the ratio of this value to that in a stagnant atmosphere is represented by the ratio of eddy diffusivity to thermal diffusivity.

Swirl in a Four-Stroke Cycle Engine Cylinder

Abstract: Air swirl speeds were measured in a motoring and firing run of a direct injection diesel engine, and the results were compared with those in steady flow tests. Experimental results show that, during the combustion period, the swirl speed in the firing condition is almost the same as that in motoring. There is a linear correlation between the swirl speed predicted from the results of the steady flow tests and that measured at top dead center in motoring. Therefore, it is recognized that the steady flow test is available to evaluate a swirl producing ability of inlet system of engine. The reduction in swirl speed during the compression period was estimated by considering the friction force acting at the air-solid interfaces.

Turbulent flame structure and speed in spark-ignition engines

Abstract: Recent exprimental, observations of flame structure and speed in spark-ignition enginesare discussed. Schlieren photographs, shadowgraphs and laser scattering measurements strongly suggest a highly wrinkled structure for the turbulent flame in such engines. Simultaneous pressure measurements and high-speed motion picture records are used to derive two closely related sets of empirical equations for calculating burning rates. One set suggests an eddy entrainment and laminar burn-out model and the other, a laminar flame stretching and wrinkling model. Tentative correlations relating the parameters in the burning equations to engine geometry and operating variables are derived. Statistical variations in the parameters produce cycle-to-cycle dispersions in the pressure, but correlations for predicting the magnitude of the dispersions have not yet been obtained.