The mixing properties of a two-dimensional reacting shear layer have been studied numerically. Effects of heat release by combustion on the mixing properties have been discussed based on the viewpoint of the transport of vorticity. The numerical simulation is concerned with an unstable, two-dimensional, two-stream, spatially developing, confined reacting shear layer. The numerical method is based on the modified HSMAC method which can handle the change in temperature. The chemical model is a one-step irreversible methane-oxygen reaction with a finite reaction rate defined by the Arrhenius law. The numerical results have revealed that in the reacting mixing layer the vorticity thickness and the carbon element mixing layer thickness defined by the difference in the carbon element mixture fraction of 99% between the fuel and the oxidizer flows, increase in comparison to the cold mixing layer. The baroclinic torque suppresses the vorticity and the viscous term to increase the vorticity thickness.

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The present study has been performed to examine the transport mechanism at the local reaction zone of turbulent premixed flames in a regime in which the Kolmogorov scale is smaller than laminar premixed flame thickness. Even in this regime, the wrinkle scale of the flame was found to depend on the characteristics of the mixture. The wrinkle scale of a propane-air turbulent premixed flame is smaller than that of a methane-air flame. Comparing the wrinkle scales under the condition of the same laminar burning velocity, the wrinkle scale of a lean methane-air and rich propane-air turbulent premixed flame was found to be smaller than the average value. These results show the effect of preferential diffusion between fuel and oxygen molecules on the wrinkle scale. Therefore, it is concluded that even in the regime in which the Kolmogorov scale is smaller than the laminar premixed flame thickness, the molecular transport mechanism still plays an important role at the local reaction zone. This conclusion contradicts the results of a previous discussion on the structure of turbulent premixed flames based on the turbulence characteristics in non-reacting flows. We should abandon such discussion.

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Combustion behaviors of pulverized coal particles suspended in a laminar upwind flow. A single pulsed YAG laser was used to heat coal particles at heating rates of l0⁵-10⁶ K/s. The rate constant of devolatilization of the bituminous coal was obtained by observing the light emission from the volatile matter combustion flame in a temperature range between l000 and 1200 K. The light intensity profiles of coal particles had two peaks and that of activated carbon showed only one peak. This indicated that two types of reaction proceeded in the devolatilization process of coal particles. The rate constant of devolatilization determined in this study agreed with the higher value among the published values determined using furnaces designed to yield heating rates of lO⁴-1O⁵ K/s.

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Fuel droplet characteristics in a flame holding region of an oil furnace (0.1MW) were investigated both in experiments and simulations. The size and shape of the recirculation flow under different conditions were examined and it was found that the simulation underestimated the size of the recirculation zone due to a κ-ε turbulent model. The size classification technique of fuel droplets was implemented in order to understand the followable characteristics of droplet in a high-turbulence region. A droplet under 30μm can follow the recirculating flow, but that over 50μm penetrates the recirculation zone due to large momentum. A conceptual flow illustration was demonstrated.

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Combusting flow simulations in an oil furnace (0.1MW) were carried out in order to investigate droplet behavior and the flame-holding mechanism. Measurements made by a phase Doppler anemometer were also examined to elucidate the followability characteristics in recirculation flow, The results show that a droplet under 30 microns can follow the flow but a droplet over 50 microns penetrates. The use of connective flux of O₂ and CO₂ both in the flame and the entire furnace was examined and the results demonstrated that it was very useful to show the self-recirculating flow in furnaces.

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The structure of a luminous, laminar, methane-air premixed flame has been investigated using gas chromatograph-mass spectrometer (GC-MS) ; a luminous flame is realized owing to energy recirculation by radiation transferred from the luminous flame to a porous medium at the upstream side of the combustion space. The results show that in the early stage of reaction the methane breaks down to C₂H₂ through a pathway similar to that of the conventional methane-oxygen premixed flame, i.e., CH₄→CH₃→C₂H₆→C₂H₄→C₂H₂ Many species, such as C₂H₂, C₄H₂ and C₆H₆, appear in the upstream region of the luminous zone ; these species play an important role in soot nucleation. Furthermore, when the concentration of these species exceeds a critical point, that is, for an equivalence ratio larger than 1.8, a luminous flame is observed.

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Laser-induced fluorescence from nitrogen dioxide (NO₂) as gas fuel tracer was applied to determine mixture stratification in a pancake type constant-volume combustion chamber using propane and hydrogen fuels. The second-harmonic output of a pulsed Nd : YAG laser was used as a light source for fluorescence excitation. the fluorescence images were corrected by a gated image-intensified CCD camera. The quantitative analysis of fuel concentration was made possible by the application of linearity between fluorescence intensity and NO₂ concentration at a low trace level. The stratified mixture (center-rich or center-lean) was concentrically formed in the central region of the chamber by a jet flow from a tangentially oriented port. The concentration difference in the radial direction of the chamber decreased with time from the start of injection. The rate of decrease was faster for hydrogen than for propane. After 300ms from start of injection, however, the time histories of the concentration (difference were nearly constant for both fuels regardless of overall concentration.

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A theoretical basis for the application of a "two-wire thermocouple" comprised of two fine thermocouples of different diameters to fluctuating temperature measurements is established with the aid of the least squares method. Based on this theory, the simultaneous in situ reconstruction of thermocouple time constants and compensated temperatures is realized without using any geometrical features of the two thermocouples such as wire diameters. Thus, introduction of a 'time-constant ratio' into the reconstruction scheme is unnecessary. Consequently, problems in two-wire thermocouple techniques proposed so far can be overcome. In addition, a simple and reliable method for correcting heat loss due to thermal radiation from the thermocouples is devised, which can be incorporated into the reconstruction scheme with little modification. The developed scheme is tested in a fluctuating temperature field with a diffusion flame formed in a two-dimensional wind tunnel, It is shown that the present technique is successful and allows us to investigate the characteristics of time-constant fluctuations in high-temperature turbulent flows.

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This study was aimed at reducing soot and nitrogen oxides by uniform and lean distribution of fuel in diesel spray using high-pressure fuel injection and a micro hole nozzle. Using a rapid compression machine with this injection system and a high-speed photographic system, we investigated the KL factor, which indicates the soot concentration and flame temperature, using the two color method. In addition to combustion analysis, we examined radical radiation which has a band spectrum in a particular wavelength range.

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For determining the optimum combination of combustion control techniques to reduce NO_x emission from diesel engines, it is important to clarify the effects of each technique not only on the NO_x emission but also on its time history during combustion. In this paper, NO_x concentration in the combustion chamber of a rapid compression machine has been measured by using a total gas sampling method. In order to elucidate the relation between NO_x history and heat release rate, air temperature, nozzle hole size and air motion are varied to control the heat release process. The results show that NO_x emission is not solely dependent upon initial combustion. Air utilization in the main diffusive combustion phase has great influence on NO_x formation and its decay. NO_x formation is accelerated by activation of the initial stage of the main combustion when using a nozzle with small holes.

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To realize clean diesel exhaust, it is very important to clarify the atomization phenomena of the fuel spray. In this study, the initial stage of the atomization process of a diesel injection fuel spray was analyzed with a high-speed image converter camera under the conditions of atmospheric gas pressure and room temperature. As a result, it was found that the initial spray formation was greatly affected by the condition inside the nozzle sac. In the case in which fuel existed in the sac, pin-like structure spray formation was observed at the initial injection stage. This phenomenon was not observed in the case in which no fuel was present in the sac, and a widely spread fuel spray formation was observed at the initial injection stage. The relatively low speed fuel spray injected in the initial low-sac-pressure condition was pushed away by the subsequent fuel spray injected in the high-sac-pressure condition.

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In order to reduce NO_x emission from a stationary diesel engine, a new prechamber, which is placed at the center of a cylinder head with a smaller volume, was installed in a single cylinder diesel engine with 170mm bore and 180mm stroke, a fundamental test apparatus was constructed, and it was tested to investigate its potential. As a result, the reduction of prechamber volume which realized rich mixture combustion in the prechamber, enlargement of jet passage area, control of fuel injection timing and reduction of intake air temperature which reduced combustion temperature, were proven to reduce NO_x emission.

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