Ryuichi Matsumoto

Structure of Turbulent Jet Flames Stabilized in Annular Air Jet

Abstract —Flame features and combustion process of fuel rich double concentric turbulent jet flames were experimentally examined. Flame appearances are very different by the velocity of the annular air jet Uam (or mass velocity ratio λ). The flames of λ = 0.25 and 0.50 for small values of Uam appear to be the conventional wrinkled laminar flames, however, for λ more than 0.74, the crowded flame appears as the result of the unburnt fuels being torn by the strong shear stress of the annular air jet and the torn–unburnt fuel crowds are intermittently ejected from the recirculation wake zone. This fact was verified by the analyses of the motion pictures and also supported by calculations of the combustion process using experimental results. Moreover, from measurements of the temperature fluctuation of the crowded flame in λ = 1.00, it was found that a comparatively high frequency fluctuation of 200∼300 Hz was superimposed on the low frequency fluctuation of 20∼50 Hz. The former corresponds with that of the mo...

State feedback and modular control synthesis in controlled Petri nets

Petri nets are useful models for discrete-event systems, and can be used in the synthesis of control. The authors introduce the concept of the weak interaction of a predicate and show that it is the necessary and sufficient condition for the uniqueness of the maximally permissive feedback. Modular control synthesis problems are represented by conjunction and/or disjunction predicates. It is also shown that the maximally permissive feedback for conjunction of component predicates exists uniquely if each predicate is weakly interactive.<<ETX>>

A compact fibre LDV with a perforated beam expander

The authors describe an optical fibre laser Doppler velocimeter (FLDV) system which consists of a manipulator that is easy to handle and a small probe. The manipulator, with a tilting mechanism of 0.3 mu m resolution, has been developed to achieve a high transmitting efficiency of laser power into a single-mode fibre. A beam expander with a perforated lens is used in the probe in order to improve the quality of the measurement volume and to reject light scattered at the front lens. The performance of the FLDV was examined by measuring the tangential velocity of a rotating disc and the longitudinal velocity of turbulent water in a pipe at three flow rates. The results show an excellent performance of the FLDV.

An Experimental Study on Low Frequency Oscillation and Flame-Generated Turbulence in Premixed/Diffusion Flames

Abstract Experimental studies were carried out on turbulences in open premixed jet flames by using a double coaxial type burner with propane-air mixtures. Shadow and schlieren graphs showed that low frequency oscillations of the flame occur in the vicinity of the boundary between the outer flame and the surrounding air stream. The phenomena are surely caused by the hydrodynamic instability and it was also asserted from the fact that the phenomena could never be seen in the case of the surrounding flow velocity being large enough in measurement by a counter-type laser doppler velocimeter (LDV). Moreover, the organized motion with periodic vortices was entirely common in premixed, rich-premixed, and diffusion flames in the open atmosphere. The normalized frequencies had a tendency similar to the results obtained by some workers On the other hand, from the measurement of velocity fields by LDV, it was found that strong turbulences occurred on the flame front mainly by the velocity gradient, not |∂∪|∂r| but |...

A study on intake flow characteristics in a two-cycle engine by a fiber laser Doppler Velocimeter.

This paper describes measurement and analysis of intake flow characteristics in a two-cycle engine which have an important effect on engine performance. For a two-cycle engine, there is close correlation between gas flow velocity and pressure. Therefore, it is necessary to elucidate these relations. The gas flows in the intake pipe were measured with a fiber laser Doppler velocimeter (FLDV) which has excellent optical properties. Furthermore, we measured the intake pipe pressure, the exhaust pipe pressure and the scavenging port pressure as well as the intake flow velocity using a developed simultaneous measurement system to clarify their mutual relations. From these measurements, the relations between gas flow velocity and pressure became obvious. In addition, the flow characteristics in the intake pipe were investigated by measuring the velocity at several measurement positions for various operating conditions.

Visualizations of flow and temperature of a thermal plume in a stably and thermally stratified fluid.

A swaying motion of thermal air plume arising from a horizontal line heat source in a stably and thermally stratified fluid is investigated experimentally. Flow and temperature visualizations of the plume were carried out. In the condition of an average heat rate from the line heat source, the amplitude of a swaying motion becomes larger and the plume transits laminar from turbulent state in the top region of the plume. In the condition of a large heat rate from the line heat source, a coherent vortex pair exists in a turbulent region of the plume. From the time-averaged temperature and the swaying spectrum of the plume, influences of the thermal stratification on the plume phenomenon were made clear. Temperature wave measurements are performed. A regular wave occurs in measured temperature profiles of laminar region. It is made clear that swaying spectrum gradients in laminar region are equal to -9/2 and -8.0. Turbulent spectrum gradients are equal to -5/3 and -3.0.