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The several burning models based on the wrinkled laminar flame concept had been proposed and applied to the turbulent premixed flame in a spark ignition engine. Fractal burning model is one of the flamelet burning models. However the formulations of fractal characteristics such as fractal dimension, inner cutoff scale and outer cutoff scale weren't established. These formulations based on the results of the fractal analysis in a constant volume vessel and a spark ignition engine were proposed in this study. The fractal dimension is expressed as a function of non-dimensional turbulence intensity and the density of mixture. Non-dimensional inner cutoff scale is expressed a function of Karlovitz number. Outer cutoff scale is equal to the flame radius. Finally the quasidimensional model for turbulent combustion was performed by using the fractal burning model with our formulations.

Hydrogen is expected to be one of the most prominent fuels in the near future for solving greenhouse problem, protecting environment and saving petroleum. In this study, a dual fuel engine of hydrogen and diesel oil was investigated. Hydrogen was inducted in a intake port with air and diesel oil was injected into the cylinder. The injection timing was changed over extremely wide range. When the injection timing of diesel fuel into the cylinder is advanced, the diesel oil is well mixed with hydrogen-air mixture and the initial combustion becomes mild. NOx emissions decrease because of lean premixed combustion without the region of high temperature of burned gas. When hydrogen is mixed with inlet air, emissions of HC, CO and CO2 decrease without exhausting smoke while brake thermal efficiency is slightly smaller than that in ordinary diesel combustion.

A path line method utilizing a CCD random shutter camera and a laser light sheet was applied for obtaining the air mass entrained into a transient gas jet. Large, light weight particles and fine particles were used for scattering the path lines of the surroundings and visualizing the approximate shape of the jet, respectively The jet configuration and the entrainment process could be visualized simultaneously, and this path line method was found to be very useful for estimating the air mass entrained because of the good agreement with the value obtained using LDA data. The spatial and temporal change of the ambient air entrainment into the jet was approximately clarified.

A turbulent gas jet impinging on a flat wall was visualized by a laser sheet method. Velocity fields were determined from the images with a high speed video system by processing them in terms of the cross correlation method for the jet and particle tracking method for the ambient air from the same images. The vortex flow near the transient jet tip impinging on the wall was visualized and analyzed successfully. The velocity field obtained from the above methods was compared to that determined with a laser Doppler anemometer. The path line of a certain period which was taken with a CCD camera with controlled shutter was analyzed and the mean rate of air entrainment was determined quantitatively. The spatial and temporal change of the entrainment rate was estimated and it was found that the entrainment rate near the upstream part of the jet tip region is larger because of the vortex.

It is necessary to understand the entrainment process of ambient air into diesel sprays for the combustion process. This study focused on the entrainment process of non-combusting and combusting hydrogen jets instead of evaporated fuel sprays because of ease with measurement for fundamental research. Spatial and temporal changes of the air entrainment into the jets were obtained using flow visualization technique. The experimental results showed that the total air mass entrained into the flame jet is nearly equal to that into the cold jet. The rate of entrainment per unit area of the flame jet is smaller than that in the cold jet. When a transient jet is separated into side and front parts, the rate of air mass entrained from the front part of the jet decreases with time while the rate into the side of the jet per unit area is almost the same. The total air mass entrained into the jet can be approximately explained by the momentum theory.

A new measuring technique of gas stream velocity has been developed, based on the phenomenon that the path of an electric discharge moves downstream under the influence of the gas stream. A probe (a thin conductive wire grounded by a resistance) is placed at a fixed distance downstream from the electrodes. When the discharge path arrives at the probe, the probe voltage rises rapidly. By means of measuring the time interval elapsing between the beginning of the spark and the rising of probe voltage, the stream velocity can be determined by the formula, U = Kℓ/τ, where K is a constant. As the result of preliminary tests, it was confirmed that the constant K is independent of distance ℓ, intensity of turbulence, temperature, and pressure of flowing gases, and depends only on the electrode spacing. The digital measurement of the time interval can be made easily.

A turbulent entrainment model is considered to be reasonable for the combustion in a spark-ignition engine. For this kind of model, it is important to estimate the turbulence characteristics, turbulent burning velocity, flame surface area and several empirical constants. Nevertheless, the examination of these values have not been examined sufficiently. In this study, a combustion model was proposed, and initiation of flame propagation, burning process of an eddy, scale of turbulence and turbulent burning velocity were discussed in detail. This model was examined under various conditions of engine speed (600-1200rpm), compression ratio (3.2-4.8) and ignition timing. The calculation results of mass fraction burned, burn rate and burn duration were in good agreement with the experimental ones. It was found that the concept of such a turbulent entrainment model was valid for predicting the combustion in a spark-ignition engine.

In a 2-stroke cycle crankcase-scavenged gasoline engine, the compositions of cylinder gas and exhaust gas were investigated by analysis of the sampled gas extracted from the cylinder and exhaust pipe. As is well known, the combustion process taking place in a 2-stroke cycle gasoline engine has cycle-by-cycle variations. In this study, a new method controlling the operation of the sampling valve was applied, which enabled us to select cycles showing the same peak pressure and to extract a combustion gas produced by the similar combustion process. From these data the following were confirmed: 1. For estimating the composition of combustion gases, simple equations of combustion reactions are available. 2. The most reliable values estimating the scavenging properties may be calculated from the change of O2 concentrations of sampled gases before and after scavenging. 3.

The structures of the turbulent premixed flame in the engine cylinder under lean burn conditions were investigated using ion probe method. The flow fields were measured with an LDA for two tumble ratios and two compression ratios. And ion-current signal was analyzed to discuss the interaction between the turbulence and the flame structure. The effects of turbulence and equivalence ratio on the characteristic values of the turbulent flame, that is to say number of ion-current peaks, thickness of flame front and thickness of burning zone of the flamelet, were investigated. In normal combustion, the structure of the turbulent flame front is almost the same as the laminar flame. In the lean limit, the flamelet is broken and stretched and then the structure may change.

In order to investigate the relation between ion current and combustion characteristics, the ion current signal from a spark plug as an ion probe, pressure history and flame development were measured in a homogeneous propane-air mixture in closed combustion chambers. The flame propagation was measured by Schlieren photography technique. When negative bias is applied to the central electrode of the spark plug, the ion current flows only due to an early flame kernel existing near the spark plug. When positive bias is applied to the central electrode, the ion current flows from the central electrode to the combustion chamber wall and to the ground electrode. Consequently, the ion current is dominated by the contact area between the flame and the combustion chamber wall. The appearance period of ion-current is related to the combustion duration. This method was applied to the combustion analysis of the spark ignition engine.