The thermoacoustic refrigerator consists of a speaker, a tube resonator and a stack of thin plates aligned paralled to the tube axis. Heat is transferred from one end of the stack to the other due to heat exchange between the oscillating gas and the plates. This refrigerator is analyzed using transfer matrices, which are based on an existing thermoacoustic theory, and a heat conduction equation including an equivalent source term. Results of this analytical method are compared with both computational and experimental ones. In addition, effects of various geometrical parameters on the coefficients of performance are calculated.

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As a result of the problem of ecological destruction due to the use of CFC, HCFC, HFC, the use of absorption refrigerators has been attracting greater attention, and improvement in the quality of these refrigerators is in demand. There are three types of solution flow for the double-effect absorption refrigerator. They are series flow, parallel flow, and the reverse flow ; each has its own characteristics. As yet little research into the differences in performance according to solution flow type has been conducted. Therefore, definitive comparison of the performances has not been made yet. This study aims to clarify the differences in the double-effect absorption refrigerator which result from the solution flow type. The differences in characteristics of double-effect absorption refrigerators driven by gas depending on the three types of solution flow were developed and compared using a simulation model As a result we were able to identify the merit of each flow type.

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The 3.39μm He-Ne infrared laser absorption technique is useful for measuring hydrocarbon concentration. To measure the concentration of propane or methane in hydrocarbon fuels, molar absorption coefficients for 3.39μm wavelength were investigated in the temperature range 285∼420K and in the pressure range l00∼800 kPa. It was found that the absorption coefficient εis independent of temperature, and the pressure has little effect on εin propane, but a strong effect on εin methane. By means of this technique, the fuel concentration in the vicinity of a spark plug and HC concentration in an exhaust pipe of a spark ignition engine were measured under the condition of no residual gas and homogeneous mixture. For the lean mixture operating condition, although cycle-to-cycle fluctuation of the fuel concentration was very small, the fluctuation of pressure in the cylinder was large.

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An advanced diffusion combustor combinig branced air nozzles and branched fuel nozzles is proposed. This type of combustor is expected to be more effective for improvig fuel/air mixing in the combustion chamber than a single-hole air-nozzle diffusion combustor. In this study, nozzle diameter is kept constant, while the angles of fuel nozzles are varied. Three kinds of combustors having fuel nozzle angles of 30°, 45°and 60°are used. For each combustor, deviation angle between air and fuel nozzles is set to be 0°, 15°and 45°, respectively. The results show that the optimum flamestability is obtained for a fuel/air nozzle deviation angle of 45°and it is unrelated to fuel nozzle angle. Furthermore, flame stability limits are much higher than those of coaxial burners.

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The flame instability induced by large vortices has been studied numerically. The numerical simulation is concerned with an unstable, two-dimensional, two-stream, spatially developing, confined, reacting shear layer. The behavior just after ignition is related to the flame instability which is affected strongly by large vortices in the mixing layer. Although flames are basically stable due to the balance between the burning velocity and the stream velocity, it is revealed that the leading edge is exposed under the strain in the mixing layer, and the flame becomes instable. Moreover, a method is also proposed to improve the flame stability by increasing the oxygen concentration in the oxidizer.

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Numerical computations are carried out for laminar jet diffusion flames taking detailed chemical kinetics and multicomponent diffusion into consideration. Attention is paid to the effects of the preferential diffusion of heat and species. The results obtained are as follows.(l) The computations predict well the experimental profiles of temperature, major species and OH radical concentration. (2) Significantly different temperatures in usual and reversed flames are predicted and verified by experiments. The excess of enthalpy and concentration of H₂ species induced by the preferential diffusion are responsible for the different temperature characteristics. (3) The preferential diffusion effects are analyzed, based on the transport equations of enthalpy and the parameter controlling the H₂ concentration, to identify the important species for the preferential diffusion. (4)The accumulation of the preferential diffusion effect along the flow affects the flame temperature significantly together with the effects of the flame curvature.

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A numerical study on the transition from laminar to turbulent flow of two-dimensional fuel jet flames developed in a co-flowing air stream was made by adopting the flame surface model with infinite chemical reaction rate and unit Lewis number. The time-dependent compressible Navier-Stokes equation was solved numerically with the equation for mixture fraction using a finite difference method. The numerical calculation was performed for the pure methane fuel jet, diluted methane fuel jet and hydrogen fuel jet, with Reynolds numbers 2 000 and 4 000. The effect of fuel containing an inert gas on the structure and the stability of the flame jet was studied. It was found that the transition length of hydrogen fuel jet was longer than that of methane fuel jet. In the downstream turbulent region, the axial velocity decreased due to the density increase, resulting in shorter flame length. Moreover, the lateral expansion of fluctuating flame surface was suppressed due to the low density inside the flame.

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Improving fuel economy and reducing emissions in gasoline engines require fine fuel atomization. This report discusses atomization characteristics of a newly developed air-assisted atomization method in which air is blown radially from an outside circumference onto the liquid film of the fuel sprayed from the upstream-swirl-type injector. This method achieves fine fuel atomization even if the air passage area is increased and air flow velocity is decreased. Moreover, air flow under the mixture spray nozzle suppresses fuel particle diffusion.

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A novel concept is proposed to realize "Ultralean Premixed Compression-Ignition Operation". Compression ignition of lean mixtures has allowed us to overcome the lean limit of flame propagation. Operating mixture strength can be decreased to an equivalence ratio of less than 0.2. Premixed fuel and air, introduced into a cylinder and compressed by piston upstroke motion, will ignite very near the top dead center. A combination of two-component fuel, namely : a low-octane liquid fuel injected into a very homogeneous high octane gaseous fuel/ air mixture just before the intake valve, enabled us to control the self-ignition timing and pressure rise rate at the onset of hot ignition. For an operating condition of engine speed and load expected in practice an optimal combination of fuel amounts can be found, i. e. the optimal octane value of the total charge and the total amount of both fuels should be selected separately for the best performance. Pure propane and n-heptane are utilized to demonstrate the feasibility of this concept. Lower fuel consumption and lower CO and NO emissions are also accomplished compared to those of spark-ignition engines.

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The optimization of regenerator performance, that is, the choice of an optimum matrix, is a key factor in the methods to raise the thermal efficiency of Stirling engines. Regenerator matrices often comprise of stacks of similar mesh size gauzes. In a fixed regenerator configuration, the size of the mesh and diameter only influence the matrix characteristics and greatly restrict the choice of the optimum matrix. In this paper, combined mesh matrices, which are composed of two stacked wire gauzes with different mesh sizes, are suggested. An approach to the design of combined mesh matrices is investigated by a simple analysis. In order to certify the matrix performance, the characteristics of three single mesh matrices and four combined mesh matrices are examined using a prototype of the semifree piston Stirling engine generator.

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In this paper, behaviors of diesel spray injected along a wall were experimentally investigated. In order to clarify the wall effect on spray structure, the geometry of the wall and its relative position to the spray axis were varied. Structures of spray injected into a high-pressure atmosphere were recorded by high-speed photographs. Results shows that the asymmetrically large vortexes in the spray were induced by the wall effect, and the spray penetrating along the wall was deviated to the wall surface. This phenomenon is called the Coanda effect in the field of fluid dynamics. The growth orientation of spray was defined by image analysis. Maldistribution ratio of spray area was defined for the quantitative estimation of the spray deviation behavior. The spray deviating conditions such as the geometry of the wall and its relative position to the spray axis were fined.

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To study the characteristics of velocity in a large-angle conical spray proposed for a premixed combustion type Diesel engine, steady and unsteady conical sprays were analyzed using a laser Doppler anemometer (LDA). The injection pressure for the steady conical spray was varied in three steps. For the unsteady conical spray, it was 19.6MPa, where the amount of injected fuel was 25.6mg per cycle, and the injection frequency was 20.7Hz. As a result, the radial distributions of mean axial-velocity for both conical sprays were similar to the Goertler distribution. The Shapes of the turbulence intensity distributions of the conical sprays and a radial gas jet were similar. Their values for the steady conical spray were smaller than that for the radial gas jet, and those for the unsteady conical spray were almost the same as that for the radial gas jet in the whole experimental region. The Reynolds stress distributions for the steady conical spray and the radial gas jet were similar but the maximum value of steady conical spray was half that of the radial gas jet. The unsteady conical spray had a value of the same order of magnitude as that of radial gas jet in the whole experimental region. The rate of decrease of the unsteady conical spray velocity was 3 times that of the steady conical spray velocity but 1/6 that of the radial gas jet velocity. The rate of air entrainment into the unsteady conical spray was half that for the steady conical spray.

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The performance of a six stroke diesel engine which has been proposed by the authors was experimentally investigated using a cyclical rapid-compression-expansion machine. The ignition delay and the maximum heat release rate in the first and second combustion processes were measured under the various conditions of wall temperature of the engine cylinder. An optical fiber probe connected to a photo sensor was installed into a combustion chamber to measure the ignition delay and to obtain the luminosity of soot exidation in the second compression process. The experimental data were compared with the numerical predictions from the 1st report. As a result, the soot oxidation phenomenon in the second compression process was numerically and experimentally confirmed. It was clarified that the experimental data of the wall temperature effect on ignition delay qualitatively agreed with the numerical prediction.

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We present that PM, which is produced in the combustion chamber of a direct-injection diesel engine, is transferred to the crankcase lubricant through the cylinder liner due to condensation of vapor. The concentration of PM in lubricant degrades lubricant in the crankcase and increases fuel consumption and corrosion and decrease the life of sliding parts of the engine. In order to minimize these disadvantages, PM purification equipment is set independent of the crankcase. As a result, the following advantages were obtained. (1) Decrease of specific fuel consumption dependent on time could be controlled. (2) Decrease of the wear on sliding parts of the engine was achieved. (3) Lubricant life was prolonged to approximately twice that of regular lubricant. (4) Improvement of specific fuel consumption of the diesel engine could be achieved.

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