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Particulate matter (PM) trapping and oxidation in regeneration on the surface of a diesel particulate catalyst-membrane filter (DPMFs) were investigated in detail using an all-in-focus optical microscope. The DPMF consists of two-layer sintered filters, where a SiC-nanoparticle membrane (made from a mixture of 80 nm and 500 nm powders) covers the surface of a conventional SiC filter. Using a visualization experiment, it was shown that PMs were trapped homogeneously along fine surface pores of the membrane's top surface, whereas in the regeneration process, the particulates in contact with the membrane may have been oxidized with some catalytic effect of the SiC nanoparticles. A soot cake was reacted continuously on the nanoparticles since pushed by a gas flow. The oxidation temperature of particulate trapped on the SiC-nanoparticle membrane was about 75 degrees lower than that on the conventional diesel particulate filters (DPF) without a catalyst.

A newly developed small-sized IES (inductive energy storage) circuit with a semiconductor switch at turn-off action was successfully applied to an ignition system. This IES circuit can generate repetitive nanosecond pulse discharges. An ignition system using repetitive nanosecond pulse discharges was investigated as an alternative to conventional spark ignition systems in the previous papers. Experiments were conducted using constant volume chamber for CH₄ and C₃H₈-air mixtures. The ignition system using repetitive nanosecond pulse discharges was found to improve the inflammability of lean combustible mixtures, such as extended flammability limits, shorted ignition delay time, with increasing the number of pulses for CH₄ and C₃H₈-air mixtures under various conditions. The mechanisms for improving the inflammability were discussed and the effectiveness of IES circuit under EGR condition was also verified.

A simultaneous multi-composition analyzing (SMCA) resonance enhanced multi-photon ionization (REMPI) system was used to investigate gasoline engine exhaust. Observed peaks for exhaust were smaller mass numbers than those from diesel exhaust. However, large species up to three ring aromatics were observed suggesting that soot precursor forms even in the gasoline engine. At low catalyst temperature condition, the reduction efficiencies of a three-way catalyst were higher for higher mass numbers. This result indicates that the larger species accumulate in the catalyst or elsewhere due to their lower vapor pressures. To evaluate the emission of low volatility species, the accumulation should be taken into account. In the hot mode, reduction efficiencies for aromatic species of three-way catalyst were almost 99.5% however, they fall to 70% in the cold start condition.

Real-time analysis of benzene in automobile exhaust gas was performed using the Jet-REMPI (supersonic jet / resonance enhanced multi-photon ionization) method. Real-time benzene concentration of two diesel trucks and one gasoline vehicle driving in Japanese driving modes were observed under ppm level at 1 s intervals. As a result, it became obvious that there were many differences in their emission tendencies, because of their car types, driving conditions, and catalyst conditions. In two diesel vehicle, benzene emission tendencies were opposite. And, in a gasoline vehicle, emission pattern were different between hot and cold conditions due to the catalyst conditions.

In order to investigate the mechanism of heat transfer on the chamber wall of direct-injection diesel engines, 2-D temperature imaging and heat flux measurement in the flame impinging region on the chamber wall were conducted using laser-induced phosphorescence technique. The temperature of the chamber wall surface was measured by the calibrated intensity variation of the 355nm-excited laser-induced phosphorescence from an electrophoretically deposited thin layer of La2O2S:Eu phosphor on a quartz glass plate placed in a rapid compression and expansion machine (RCEM). Instantaneous 2-D images of wall temperature at different timings after start of injection and time-resolved (10kHz) heat flux near the flame impinging region were obtained for combusting and non-combusting diesel sprays with impinging distance of 23.4mm at different injection pressures (80 and 120MPa).

In this study, the combustion characteristics of diesel flame achieved in a rapid compression and expansion machine (RCEM) at various patterns of oxygen distribution in the chamber are investigated in order to clarify the effect of heterogeneity of oxygen distribution in diesel engines induced by EGR on the soot and NOx emissions. To make the heterogeneous distribution of oxygen in a combustion chamber, the mixtures with different oxygen concentrations are injected through the each different port located on the cylinder wall. Results indicate that the amount of oxygen entrained into the spray upstream the luminous flame region affects the NO emission from diesel flame strongly.

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.

In order to investigate the soot formation process in a diesel spray flame, simultaneous imaging of soot precursor and soot particles in a transient spray flame achieved in a rapid compression machine was conducted by laser-induced fluorescence (LIF) and by laser-induced incandescence (LII) techniques. The 3rd harmonic (355nm) and the fundamental (1064nm) laser pulses from an Nd:YAG laser, between which a delay of 44ns was imposed by 13.3m of optical path difference, were used to excite LIF from soot precursor and LII from soot particles in the spray flame. The LIF and the LII were separately imaged by two image-intensified CCD cameras with identical detection wavelength of 400nm and bandwidth of 80nm. The LIF from soot precursor was mainly located in the central region of the spray flame between 40 and 55mm (270 to 370 times nozzle orifice diameter d0) from the nozzle orifice. The LII from soot particles was observed to surround the soot precursor LIF region and to extend downstream.

Multi-step water splitting with Mn-ferrite(MnFe2O4)/sodium carbonate(Na2CO3) system accompanying endothermic reaction was investigated for converting solar energy into chemical energy. This water splitting is caused by the oxidation-reduction of manganese ion in the Mn-ferrite. Multi-water splitting with MnFe2O4/Na2CO3 system was consisted of three steps. The first step was hydrogen generation at 1073K. The second step was oxygen release at 1273K. The third step was Na2CO3 reproduction at 873K. The mechanism of multi-water splitting has been considered by XRD, chemical analysis of colorimetry and back titration. The temperature range 873 to 1273K is quite lower than those studied on the solar furnace reaction (O2 releasing step) in two-step water splitting (1500-2300K). This lower temperature range would permit further progress in converting the direct solar energy into chemical energy.

A thermodynamic two-zone model which assumes a stoichiornetric burned gas region and unburned air region is presented in an attempt to calculate more precise rate of heat release of diesel combustion. A comparison is made of the rate of heat release obtained by the two-zone model with that obtained by the conventional single-zone model. It shows around 10 % increase in the rate of heat release with the two-zone model. The effect of state equation of gas is also examined with the single-zone model and the use of a real gas law in stead of the perfect gas law is found to yield minor difference in the rate of heat release at a high boost operating condition.

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.

A one-dimensional numerical calculation has been performed on a new reciprocating heat engine proposed on the basis of super-adiabatic combustion in porous media. The system consists of two pistons and a thin porous medium in a cylinder; one being a displacer piston and the other a power piston. These create reciprocating motions with a phase relation angle. By means of the reciprocating flow system, the residual combustion gas enthalpy is effectively regenerated to induce enthalpy increase in the mixture through the porous medium. Due to heat recirculation, the thermal efficiency reaches to 58% under the condition of the compression ratio of 2.3.

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.

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.

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.

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.

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.

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.

The relation between the characteristics of a non-evaporating spray and those of a corresponding frame achieved in a rapid compression machine was investigated experimentally. The fuel injection pressure was changed in a range of 55 to 260 MPa and the other injection parameters such as orifice diameter and injection duration were changed systematically. The characteristics of the non-evaporating spray such as the Sauter mean diameter and the mean excess air ratio of the spray were measured by an image analysis technique. The time required for a pressure rise due to combustion was taken as an index to characterize the flame. It was concluded that the mean excess air ratio of a spray is the major factor which controls the burning rate and that the high injection pressure is effective in shortening the combustion duration and reducing soot formation.