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A prediction model of the cycle-to-cycle variation of the in-cylinder flow in IC engines which employs the time averaged k-ε turbulence model is proposed. The concept is based on an assumption that the power spectrum of the cycle-to-cycle variation can be deduced from the power spectra of both the mean velocity and turbulence intensity. To validate this model, in-cylinder velocity measurement in a transparent cylinder engine with a 2-valve cylinder-head is made using an LDV system. Comparisons of in-cylinder flow fields between the calculation and measurement show a good agreement in the cycle-to-cycle variation as well as the turbulence intensity. Finally, this model is applied to three kinds of flow fields to examine how the cycle-to-cycle variation may be effected. As a result, it is found that the swirl flow is effective to reduce the cycle-to-cycle variation, while the tumbling flow enhances the turbulence generation around the compression TDC.

To understand further the mixing process between the injected fuel and air in the combustion chamber of a diesel engine, the turbulent mixing process in a one-phase, two-dimensional transient jet was theoretically studied using the discrete vortex simulation. First, the simulation model was evaluated by comparisons between calculated and experimental data on two-dimensional turbulent jets. Second, the trajectories of the injected fluid elements marked with different colors were graphically demonstrated. Also the process of entrainment of the surrounding fluid into the jet was visually presented using colored tracers.

To measure the fuel vapor concentration in an unsteady evaporating spray injected into nitrogen atmosphere, the exciplex-forming method, which produces spectrally separated fluorescence from the liquid and vapor phase, was applied in this study. Two experiments were conducted to investigate the qualitative and quantitative applicability of the technique in a high temperature and high pressure atmosphere during the fuel injection period. One is to examine the thermal decomposition of TMPD dopant at a high temperature and a high pressure nitrogen atmosphere during a short period of time. The other is to calibrate the relationship between fluorescence intensity and vapor concentration of TMPD at different vapor temperatures. And then, the qualitative measurement of fuel vapor concentration distributions in diesel sprays was made by applying the technique.

The cross-sectional distribution of fuel vapor concentration in an evaporating spray was measured quantitatively by a new scattering imaging technique, silicone particle scattering imaging method, which was proposed in a previous paper[1]. When fuel containing silicone oil injected into a nitrogen environment at high temperature, the volatile base fuel in the droplets vaporized rapidly, leaving behind small droplets of silicone oil suspended in the vapor-gas mixture. The silicone oil droplets were illuminated by a thin laser sheet, and the scattered light was imaged by a CCD camera. The cross-sectional distribution of vapor concentration was estimated from the scattering image of the silicone oil droplets by Mie scattering theory. The results demonstrated clearly the inhomogeneity of the fuel vapor concentration. The distribution of vapor concentration was discontinuous, and islands of rich mixture with a scale of several millimeters existed in the center region of the spray.

Local heat flux from the flame to the combustion chamber wall, q̇, was measured the wall surfaces of a rapid compression-expansion machine which can simulate diesel combustion. Temperature of the flame zone, T1, was calculated by a thermodynamic two-zone model using measured values of cylinder pressure and flame volume. A local heat transfer coefficient was proposed which is defined as q̇/(T1-Tw). Experiments showed that the local heat transfer coefficient depends slightly on the temperature difference, T1-Tw, but depends significantly on the velocity of the flame which contacts the wall surface.

Soot concentration is very high in the periphery near the head of an unsteady spray flame which is achieved in a quiescent atmosphere in a rapid compression machine. To reduce soot concentration in this region, it was intended to improve fuel-air mixing by letting the flame impinge on a turbulence-generating plate. Two types of turbulence-generating plates, one donut-type, the other cross-type, were tested. Soot concentration in the flame was imaged using the laser shadow technique. The effect of injection pressure on soot reduction by the flame impingement was also investigated. The overall soot concentration is reduced significantly in the case when the flame impinges on the cross-type turbulence-generating plate at 50 mm (333 nozzle diameters) from the nozzle exit. The flame impingement on the cross-type turbulence-generating plate at 333 nozzle diameters makes soot reduction little dependent on injection pressures.

Air-entrainment characteristics of non-evaporating sprays and flames were measured by means of high-speed photography including ordinary shadowgraphy of sprays, back diffused light illumination photography and laser shadow photography of flames. Effects of injection pressure and nozzle orifice diameter on air-entrainment characteristics were investigated parametrically. The amount of air entrained into a flame was calculated by a two-zone thermodynamic model with data obtained from the photographs and the pressure measurement in the combustion chamber. The air-entrainment characteristics of flames were compared with those of the corresponding sprays. It showed that immediately after the start of ignition, the air entrainment into a flame increased more rapidly as compared with the corresponding spray and then, with the development of diffusion combustion, the air entrainment gradually approached that of the spray.

A new method to determine simultaneously the temperature and the fuel vapor concentration inside an evaporating spray was described by using a laser-induced fluorescence technique. A TMPD doped base fuel composed of C12H26: 22%, C13H28: 54% and C14H30: 30% was injected into the combustion chamber of a rapid compression machine which is filled with a high temperature and high pressure nitrogen. The laser sheet was used for incident light, which was reflected by a prism located inside the combustion chamber and propagated through the center of an evaporating spray. The laser induced fluorescence intensity was imaged by a high speed-gated intensifier from a direction perpendicular to the incident light. The results shows that mixtures with high equivalence ratio are observed in the central region, while low equivalence ratio mixtures are observed in the periphery of the spray. It is also observed that the temperature of richest mixture is 50 K as low as the surrounding gas temperature.

A rapid compression-expansion machine was developed, which can simulate intake, compression, expansion and exhaust strokes in a single Diesel cycle by an electrically controlled and hydraulically actuated driving system. The whole system which is composed of a hydraulic actuator, fuel injector and a valve driving device, is sequentially controlled by a micro-computer. The machine features; 1) accurate control of piston position at TDC, 2) no effect of lubricant on HC emission due to the use of dry piston rings; 3) independent control of local wall temperature; and 4) high power output to drive heavy piston at high frequency. The single cycle operation permits Diesel combustion experiments under a wide range of operating conditions and easy access of optical diagnostics with minimized amount of test fuel. The performance test showed that the machine can drive a DI Diesel type piston with a 100 mm bore at a maximum frequency of 16.7 Hz at a maximum compression pressure of 15 MPa.

In an attempt to achieve lean combustion in Diesel engines which has a potential for simultaneous reduction in no and soot, the authors developed a micro-hole nozzle which has orifices with a diameter as small as 0.06 mm. Combustion tests were carried out using a rapid compression-expansion machine which has a DI Diesel type combustion chamber equipped with the micro-hole nozzle. A comparison with the result of a conventional nozzle experiment revealed that the ignition delay was shortened by 30 %, and in spite of that, both peaks of initial premixed combustion and diffusion combustion increased significantly. The combustion in the case of the micro-hole nozzle experiment was accompanied with a decrease in soot emission, whereas an increase in NO emission.

The turbulent dispersion of particles in an unsteady two dimensional particle-laden jet was simulated by a discrete vortex method coupling with a model of gas/particles interaction. Numerical analysis of a spray yielded the distributions of vorticity, fuel mass concentration and local Sauter mean diameter (SMD) of droplets in a spray. The predicted distribution of local SMD of droplets in a spray demonstrated that the size of droplets in the spray periphery is larger than that of droplets in the center region of spray. This trend of distribution of drop size coincided with that of measured one. The predicted distributions of drop size and vorticity revealed that the larger droplets are easily centrifuged to the periphery of the spray. The effects of the pattern of injection rate on the mixing process in a transient spray were also investigated.

Two kinds of planar soot imaging techniques, laser induced incandescence (LII) and laser induced scattering (LIS) techniques were applied simultaneously to an unsteady free spray flame achieved in a rapid compression machine. An analysis of LII and LIS images yielded three kinds of qualitative images of soot concentration, size of soot particles, and number density of soot in the flame. These images revealed the fact that the soot is formed mainly in the center region of a flame resulting in an appearance of soot cloud with high number density and small particle size in this region, and then the soot size increases and the number density decreases while soot is conveyed downstream.

Local inhomogeneity of mixture concentration affects combustion characteristics in the lean burn system and also in the stratified charge combustion system. To investigate such combustion systems, the effects of inhomogeneous mixtures were examined using a carefully controlled experimental system. In this study, a constant-volume chamber, which can simulate an idealized stratified charge by using a removable partition inside the chamber, was developed. Flow and combustion characteristics were examined by indicated pressure analysis, Schlieren photography, ion probe measurements and local equivalence ratios measurements while varying the combination of initial equivalence ratios on each side of the partition. As a result, combustion characteristics of charge stratified, very lean propane-air mixture were clarified.

The local heat fluxes from impinging combusting and evaporating diesel sprays to the wall of a square combustion chamber were measured in a rapid compression machine. It was revealed that the ratio of local heat flux between the combusting and evaporating spray, q̇c/q̇e, is of the same order of magnitude as (Tc-Tw)/(Te-Tw) and its values estimated by a two-zone model agree roughly with the measured ones. The time-mean local heat flux during the spray impingement was found to be approximately proportional to the 0.8th power of the injection velocity and the heat-transfer phenomenon depends largely on whether the ignition starts before or after the impingement.

In order to investigate early soot formation process in diesel combustion, spectral analysis and optical thermometry of early soot formation region in a transient spray flame under diesel-like conditions (Pg2.8 MPa, Tg620-820K) was attempted via laser-induced fluorescence (LIF) from pyrene (C16H10) doped in the fuel. Pyrene is known to exhibit a temperature\-dependent variation of LIF spectrum; the ratio of S2/S1 fluorescence yields, from the lowest excited singlet state S1 and the second excited singlet state S2, depends on temperature. In the present study, pyrene was doped (1%wt) in a model diesel fuel (0-solvent) and the variation of LIF spectra from the pyrene in the spray flame in a rapid compression machine were examined at different ambient temperatures, ambient oxygen concentrations, measurement positions and timings after start of fuel injection.

As a basic tool for fundamental studies on combustion and heat transfer in diesel engines, a new rapid compression machine with a cylinder bore of 200 mm was developed which can realize in it a free diesel flame in a quiescent atmosphere, a diesel flame in a swirl, and a diesel flame impinging on the wall. The piston of this machine is driven by high pressure nitrogen, and its speed is controlled by a sophisticated hydraulic system. This paper describes the details of the mechanism and performances of the machine, and presents some examples of studies conducted with this machine.

A new technique was proposed for measuring instantaneous distributions of flame temperature and KL factor of luminous flames. Here the principle of the two-color method was used to calculate flame temperature and KL factor from the two-color densities of a film image taken on a nega-color film. We applied this technique to the high speed nega-color photographs of flames in a D. I. diesel engine operated with varying swirl ratios, and discussed the measured results of instantaneous distributions of flame temperature and KL factors.

A diesel spray and flame in a quiescent atmosphere were realized without interference with combustion chamber walls in a newly constructed rapid compression machine. High speed shadow photography and pressure measurement were employed to obtain data for calculating the amount of air entrainment into the the flame and spray. From a comparison of air entrainment between the flame and spray, it turned out that when ignition delay becomes longer air entrainment into flames is promoted by the thermal expansion of multi-points ignition sources in the central region of the spray.

Some problems associated with applying LDA to the measurement of air motion in the engine’s cylinder are studied experimentally for both the forward and the back scattering technique in a motored diesel engine. The effects of the doppler broadening caused by the velocity gradient and the diameters of the scattering particles are discossed. The decaying process and the structure of the in-cylinder flow field are studied using the measurements of the main flow velocity, the turbulent intensity and macro scales and normalised power spectrum of the turbulence. A comparison measurement is also made between the forward scattering and the back scattering techniques.

Flame temperature and KL factor in a DI diesel engine are measured optically by the two-color method. Some differences are observed between the measure values at visible and infrared wavelengths. These differences are caused by: (1) effect of change of index α in time at infrared wavelength during combustion period; (2) effect of distributions of temperature and soot concentration along optical path; and (3) effect of reflection at the walls. The optical characteristics and some other problems on the instrumentation of the two-color method at both wavelengths are also discussed.