This article provides an overview of the combustion and emission characteristics of the low-heat-rejection (LHR) diesel engine, the characteristic feature of which is that its combustion chamber wall components are of ceramic materials. The combustion chamber wall temperature of the LHR engines, which operate without cooling, increases more significantly at the high load condition compared with corresponding temperature of the water-cooled engines. The increased compression air temperature, which is due to the elevated temperatures of the combustion chamber walls, leads to a short ignition delay and increased combustion temperature. Combustion in LHR engines, therefore, is characterized by reduced premixed combustion and increased diffusion combustion. Degradation in combustion at high combustion temperature which results in a lower heat release rate and prolonged combustion duration may be attributed to poor mixing due to increased gas viscosity. The high combustion temperature and the change in the combustion mode are two competing influences that determine either the increase or the decrease in emissions such as NO, HC and particulates.

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When a viscoelastic fluid jet falling vertically encounters a deformation from the horizontal direction, the jet shows an anomalous behavior very different from that of a Newtonian fluid jet. We observe the deformation behavior of the jet in detail and find that the jet behavior is divided into two conditions. Moreover, we derive an empirical formula of the transition point, making use of the dimensional analysis method.

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In supersonic centrifugal compressor or disc MHD power generators, oscillation modes of the circular shock wave can be caused by the static change or the dynamic change of the back pressure. While previous studies, which included only the former effects, were carried out both experimentally and theoretically, the latter effects of forced oscillation are considered here. The excitation of the back pressure fluctuation in a downstream stagnation chamber was accomplished by rotating a butterfly valve. The pressure fluctuation was measured to investigate the resonance of the circular shock wave at concentric positions in the vicinity of the first shock and in the downstream stagnation chamber. A-D converted signals were statistically correlated to extract the spacial oscillation modes. Resonance was confirmed to occur when the excitation frequency was near the natural frequency of mode 0. Furthermore, the small pertubation of the higher harmonic modes in the downstream stagnation chamber influenced the oscillation modes of the circular shock wave.

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A turbulent flow in a two-dimensional channel with fluid injection from one wall has been numerically simulated by large eddy simulation (LES). The Reynolds number based on the channel width and bulk velocity is 4900. The total grid number used in the calculation is about 1.23 million, which allowed a highly resolved turbulent flow simulation. In the flow field, events of production, redistribution and dissipation of turbulent energy are observed in streamwisely separated locations. Therefore the LES data are instrumental in understanding the turbulence structure as well as in investigating turbulence models. The present result shows that the pressure-strain terms in Reynolds stress equations are related to the streamwise vortices with intensified pressure fluctuation, rather than to the direct isotropization.

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Experiments were performed in a two-phase (gas-solid), plane mixing layer to study the behavior of heavy particles in an intermittent shear flow. The high-speed stream inlet velocity was fixed at 10.5m/s and the inlet velocity ratio was 0.377. The low-speed stream was seeded with 30- and 50-μm-diameter particles. Particle and gas velocity statistics were obtained in flows subjected to accelerating, neutral, and adverse pressure gradients. These data support the proposal that particle dispersion is strongly affected by the large-scale vortical structures of the mixing layer. The streamwise pressure gradient effects particle dispersion through changes induced in the behavior of these vortices. In these experiments, lateral transport was favored in the flow in the contraction where the mixing layer expands into the particle feedstream. The relative insensitivity of particle turbulent velocities to pressure gradient may be attributed to the independence of the Stokes number and d<P>/dX. Particle inertia and the anisotropy of the gas turbulence structure result in large differences in streamwise and transverse particle velocity fluctuations. Particle inertia may also account for the observed dependence of particle lag on the streamwise pressure gradient.

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In this paper, the analytical method developed previously for oscillating cascades was refined to deal with cascades with steady aerodynamic loading. The unsteady aerodynamic force acting on the linear oscillating cascades with tip clearance was calculated numerically by means of a vortex lattice method. Tip vortices were assumed to consist of linear vortex segments, and their paths were determined on the basis of experimental results measured using a 5-hole Pitot tube. The calculated damping forces showed good agreement with the corresponding experimental data. The effect of tip clearances on the flutter boundary was also investigated, and it was revealed that the cascade flutter was suppressed owing to the presence of tip clearances. When the blade oscillation was destabilized, it was found that the unsteady aerodynamic force became the exciting force at the blade-tip side sooner than at the hub side.

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Cavitation tests were carried out on a Darrieus-type cross-flow water turbine, which could be put into practical use for small water power. In the present paper, cavitation phenomena occurring on the Darrieus runner with various blade sections are explained and the characteristics of the incident cavitation coefficient for the attack angles in relative flow around the Darrieus blades are also evaluated with theoretical considerations of the difference between the circular motion of the Darrieus blades and the linear motion of those in a uniform steady flow. As the result, a useful method is proposed for estimating the required net positive suction head (NPSH) of a Darrieus-type water turbine.

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An experimental investigation was performed for drypatch characteristics prediction based on the transient heated surface temperature and static pressure characteristics, using a flat-plate-type obstacle in a rectangular channel. A relationship was obtained between the drypatch occurrence and the transient heated surface temperature in the obstacle and its downstream side using a map of the drypatch occurrence around the obstacle. The mechanism and places of drypatch occurrence were investigated using the boiling number Bo, regarding heat transfer, and the steam Weber number We_v, regarding fluid flow, as factors affecting drypatch phenomena. There was a good correlation for drypatch occurrence between the steam Weber number and higher transient heated surface temperatures.

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Entrainment behavior on a density interface of stratified fluids is very important for the design of innovative nuclear reactors. In the present study, the turbulent energy in the upper stratified fluid was supplied by an injection and extraction flow. The turbulent intensity in the upper fluid was proportional to the injection and extraction velocity at the nozzle. The entrainment was done by liftup of filaments from peaks of the interfacial wave. The entrainment velocity was inversely proportional to the overall Richardson number. These results could be obtained when the turbulent energy released from the energy-containing eddy was proportional to the energy consumption by the entrainment.

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A series of experiments was performed that covered the entire range of expansion and collapse of an underwater bubble in the vicinity of a rigid wall. These experiments have been successfully simulated using a new arbitrary Lagrangian Eulerian hydrodynamic computer program which can run numerical simulations of practical bubble problems in 10 to 20 minutes of CPU time on a CRAY-YMP at an overall rate of 80 MFLOPS.

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The distribution of the local void fraction across a section of a conduit was studied experimentally in air-water two-phase flow flowed through a pipe junction with the branching angle of 90°and the area ratio of unity. As in the previous report, the main conduit of the pipe junction was set up vertically, and upward air-water bubbly and slug flows were produced in the main upstream section. If the flow regime, the quality and the ratio of lateral mass flow discharge of water to total mass flow discharge of water are equal, the larger the Reynolds number is, the more violent the variety of the local void fraction distribution adjacent to the branching point in the lateral conduit is. However, the variety in the main downstream section is hardly influenced by the Reynolds number.

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A large-scale stack model of a molten carbonate fuel cell was developed for evaluating the variation of cell performance and temperature in the cell-stacking direction. A numerical method for the performance and three-dimensional temperature distribution in the stack was proposed and examined. For the temperature distribution, calculated results, taking the heat transfer at the end plate surface into account, were compared with the measured temperature distribution of the cell stack with good agreement. For several stacks composed of 12 cells with different gas flow configurations, the total stack performance and the temperature distribution were investigated analytically. The temperature distribution of the cell becomes more uniform due to the effect of heat exchange in the stacking direction.

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Many papers have described heat transfer in a regenerator core. We tried to obtain an approximate solution of original partial differential equations dealing with heat transfer between gas and core. The exact solution of the original equation is so complicated that the equations were converted to simultaneous ordinary differential equations by using the finite difference form. We obtained the approximate solution described here and inspected it for accuracy. We then applied it to the evaluation of the heat transfer rate of a model core. This method was compared to the maximum slope method, and the precision of the calculated results was verified.

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The burning and extinction characteristics of a methane diffusion flame in corotating and counterrotating counterflows are experimentally and theoretically investigated. On the basis of the large activation energy asymptotics and the similarity solutions, theoretical predictions are in favorable agreement with the experimental observations on variations of the flame temperature, the flame position and extinction condition with the angular velocity. Results show that by increasing the angular velocity, the flame temperature of a strong diffusion burning is increased to maximum and then decreased ; however, the methane concentration at flame extinction is decreased to minimum and thereafter increased without regard to either corotating or counterrotating counterflow. On the flame extinction, the linear envelope of the extinction curve is valid only for the injection velocity larger than 25cm/sec in rotating counterflows. The extinction profile for smaller injection velocity is curved for both rotating and nonrotating counterflows. Finally, it is found that the absolute minimum fuel concentration on local extinction for diffusion burning cannot be properly identified by the linear extrapolation of the extinction curve.

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A two-stage entrained-bed coal gasifier has the feature that the entire coal gasifier can be operated at a low air content by controlling the coal and air feed rates to the combustor and the reductor section, respectively, independently. This paper describes the results of computer analysis on the different coal feed ratios to the combustor and the reductor before the test with our 2t/day coal gasifier. The main results are as follows : (1) We can expect a higher cold gas efficiency and calorific value at a lower combustor/reductor coal feed ratio with the temperature of the raw gas at the combustor section kept constant ; (2) In general, it is effective to lower the coal feed rate with the entire air feed ratios kept constant for efficiently gasifying the high-ash-fusion-temperature coal, but we assume that a high temperature cannot be obtained at the combustor section because the heat loss through the 2t/day gasifier wall tends to sharply increase at a lower combustor/reductor feed ratio.

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We examined the possibility that indirect heating by radiant tubes in a continuous annealing process in the steel industry may be replaced with direct flame heating without the oxidation of metal surfaces. Energy and capital savings are expected as a result of this new-concept technology. The possibility of its practical application has been proved although the successful operating conditions are sensitive to the controlling factors. To realize this concept, the residual oxygen concentration in a flame must be lower than 0.1% (v/v), and the volume ratios of CO/CO₂ and H₂/H₂O in the flame should be over 0.4 and 0.09, respectively.

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Department of Applied Physics, The National Defense Academy / Nomura Securities Investment Trust Management Co. Ltd. / Ricoh Co. Ltd. / Department of Mechanical Engineering, Keio University / Department of Mechanical Engineering, Keio UniversityIn order to examine thermophysical properties and cycle analysis for a nonazeotropic mixture of the Refrigerant 22 (CHClF₂) + Refrigerant 114 (CClF₂CClF₂) system, an equation of state coupled with empirical mixing rules was formulated based on the available PVTx measurements taking thermodynamic consistency into consideration. The developed equation of state is expressed by the Helmholtz function as a function of temperature, density and composition, and is effective for a range of temperatures from 250 to 500K and of pressures up to 10MPa, which corresponds to the density range up to the critical value. With the aid of the proposed equation, the cycle analysis on the heat pump and refrigeration systems was theoretically carried out, and it became clear that the Refrigerant 22 + Refrigerant 114 system is promising for industrial heat pumps or air-conditioning and hot-water-supply heat pump systems. It was confirmed that the effect of change in composition on the theoretical coefficient of performance had the same behavior as that reported by experimental testing.

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