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In order to extend the HCCI high load operational limit, the effects of the distributions of temperature and fuel concentration on pressure rise rate (dP/dθ) were investigated through theoretical and experimental methods. The Blow-Down Super Charge (BDSC) and the EGR guide parts are employed simultaneously to enhance thermal stratification inside the cylinder. And also, to control the distribution of fuel concentration, direct fuel injection system was used. As a first step, the effect of spatial temperature distribution on maximum pressure rise rate (dP/dθmax) was investigated. The influence of the EGR guide parts on the temperature distribution was investigated using 3-D numerical simulation. Simulation results showed that the temperature difference between high temperature zone and low temperature zone increased by using EGR guide parts together with the BDSC system.

In a motorcycle gasoline engine, the port fuel injection system is rapidly spread. Compared to an automotive engine, the injected fuel does not impinge on the intake valve due to space restriction to install the injector. In addition, as the air flow inside the intake pipe may become very fast and has large cycle-to-cycle variation, it is not well found how the injector should be installed in the intake pipe to prepare “good” fuel-air mixture inside the intake pipe. In this study, the formation process of the fuel-air mixture is measured by using ILIDS system that is a 2-D droplets' size and velocity measurement system with high spatial resolution. Experiments with changing conditions such as flow speed and injection direction are carried out. As a result, the effects of injection direction, ambient flow speed and wall roughness on the fuel-air mixture formation process was examined, considering the three conditions of cold start, light to medium load operation and high load operation.

Control of turbulence during the compression stroke is suggested by both theoretical calculations and experimental results obtained with an LDV measurement in a motored engine. The authors have found experimentally that when an axial distribution of swirl intensity exists, a large-scale annular vortex is formed inside the cylinder during the compression stroke and this vortex generates and transports turbulence energy. A numerical calculation is adopted to elucidate this phenomenon. Then, an axial stratification of swirl intensity is found to generate a large-scale annular vortex during the compression stroke by an interaction between the piston motion and the axial pressure gradient. The initial swirl profile is parametrically varied to assess its effect on the turbulence parameters. Among calculated results, turbulence energy is enhanced strongest when the swirl intensity is highest at the piston top surface and lowest at the bottom surface of the cylinder head.

In this study, the characteristics of diesel spray droplets, such as the velocity and the diameter were simultaneously measured by using an improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method on a 2D plane to evaluate the droplet breakup modeling. In numerical analysis, DDM (Discrete Droplet Model) was employed with sub-models such as droplet breakup, droplet drag force and turbulence. Experiments have been performed with an accumulator type unit-injector system and a constant-volume high-pressure vessel under the condition of quiescent ambient gas. The injection pressure and ambient gas pressure were set up to 100 MPa and 0.1 / 1 MPa, respectively. The nozzle orifice diameter was 0.244 mm with a single hole. The measurement region was chosen at 40 ∼ 60 mm from the nozzle-tip. Numerical analysis of diesel sprays was conducted and the results were compared to the measured results.

In order to measure the spatial distribution of fuel jet concentration quantitatively, a technique combining methods of fluorescence with absorption was developed. LIF method can obtain the spatial fuel distribution qualitatively, but quantitative measurement is difficult. Meanwhile, laser-beam absorption method can quantitatively obtain the integrated jet concentration on the light-path. In addition, scanning the laser-beam allows for a quasi 2-D quantitative measurement of the jet concentration. Firstly, in this study, this measurement system was tested in a homogeneously charged field while varying the dopant NO2 concentration, the laser-beam scanning speed, and the ambient pressure. As a result, some data-correction techniques were developed to produce a quantitative measurement. Secondly, this system was applied to gaseous jet fields in a constant volume bomb.

Because the two-stroke gasoline engine has a feature of high power density, it might become a choice for automobiles' power train if the high HC exhaust emissions and high fuel consumption rate could be improved. As the GDI technology is quite effective for two-stroke engines, a Schnurle-type small engine was modified to a GDI engine, and its performance was tested. Also, numerical analysis of the mixture-formation process was carried out. Results indicated it was possible to reduce both the HC emissions and fuel consumption drastically with the same maximum power as a carbureted engine at WOT condition. However, misfiring in light load condition was left unresolved. Numerical analysis clarified the process of how the mixture formation got affected by the injector location, injection timing, and gas motion.

The purpose of this study is to investigate the turbulent mixing in a diesel spray by large eddy simulation (LES). As the first step for the numerical simulation of diesel spray by LES, the LES of transient circular gas jets and particle laden jets were conducted. The simulation of transient circular jets in cylindrical coordinates has numerical instability near the central axis. To reduce the instability of calculation, azimuthal velocity around the central axis is calculated by the linear interpolation and filter width around the axis is modified to the radial or axial grid scale level. A transient circular gas jet was calculated by the modified code and the computational results were compared with experimental results with a Reynolds number of about 13000. The computational results of mean velocity and turbulent intensity agreed with experimental results for z/D>10. Predicted tip penetration of the jet also agreed to experimental data.

The two-dimensional distribution of a soot cloud in an unsteady spray flame in a rapid compression machine(RCM) was visualized using the laser sheet scattering technique. A 40 mm x 50 mm cross section on the flame axis was illuminated by a thin laser sheet from a single pulsed Nd:YAG laser(wavelength 532 nm). Scattered light from soot particles was taken by a CCD camera via a high speed gated image intensifier. The temporal variation of the scattered light images were presented with the injection pressure as a parameter. The results showed that scattered light was intense near the periphery of the flame tip and that the scattered light becomes weaker significantly and disappears fast after the end of injection as injection pressure is increased. This technique was also applied to the visualization of the two-dimensional distribution of liquid droplets in the non-evaporating spray to correlate it with the soot concentration distribution.

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.

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.

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.

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.

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.

A new method was developed which measures the atomization characteristics of a non-evaporating, axisymmetric diesel spray: The film image density of the high speed focused shadow photographs of a spray was analyzed based on the incident light extinction principle, and the Sauter mean diameter and the fuel concentration distribution were calculated from the image data and the measured injection rate with the help of the onion peeling model. The measured Sauter mean diameter showed good agreement with the diameter measured by the conventional immersion method, and also the measured fuel concentration distribution along the spray axis was proved to coincide well with the predicted result by Che one dimentional quasi-steady jet model except at a region near the spray tip.

A phenomenological model for predicting the rate of heat release of an axisymmetrical diesel flame which was achieved in a rapid compression machine has been proposed: Basing on the experimental observations, authors have introduced a new expression about the effects of abrupt thermal expansion due to the initial combustion on the air entrainment. A simple probability density function was also employed to express the distribution of the local equivalence ratio in the flame. The predicted rate of heat release showed good agreement with the experimental results in the diffusion combustion phase.

The swirl velocity in the combustion bowl of a DI diesel engine was measured by means of laser doppler anemometry, varying the swirl intensity and engine speed. At the same time an axisymmetrical two dimensional laminar model for simulating the in-cylinder air motion was presented. The boundary condition of the flow near the wall was investigated by a comparison of predicted and measured swirl velocity, and as a result the free slip condition was found to be suitable for the present model. A comparison between measured and theoretical swirl velocity revealed that the secondary flow in the combustion bowl induced by an interaction between the squish and swirl flow transfers swirl velocities from points to points, causing a complex time variation of the swirl velocity at an observing point.

The purpose of this paper is to find a way to extend the high load limit of homogeneous charge compression ignition (HCCI) combustion. This paper presents the effect of in-cylinder flow and stratified mixture on HCCI combustion by experiments and three-dimensional computer fluid dynamics coupled with a detailed chemical reaction calculation. The first study was conducted using a rapid compression and expansion machine (RCEM) equipped with a flow generation plate to create in-cylinder turbulent flow and with a control unit of in-cylinder wall temperature to create in-cylinder temperature distribution. The study assesses the effect of the turbulent flow and the temperature distribution on HCCI combustion. In the second study, the numerical simulation of HCCI combustion was conducted using large eddy simulation coupled with a detailed chemical reaction calculation. The study analyzes the interaction between in-cylinder turbulent flow and mixture distribution and HCCI combustion.

Resistive particulate matter sensor (PMS) is a promising solution for the diagnosis of diesel/gasoline particulate filter (DPF/GPF) functionality. Frequently triggered regeneration of their sensing element, for cleaning the soot dendrites deposited on the surface, leads to experience high temperature and thermal stress and pose high risk of developing cracks in the electrodes or sensing substrate. A semiconductor with a dopant concentration of 100 ppm~10000 ppm is applied as a sensing element for PMS self-diagnosis. Upon cooling at air, the polarization doped-insulating layer in a resistive PMS starts to resume the electrical conductivity in the wake of experiencing high regeneration temperature, through the electron and hole directional mobility.

The analysis of spray characteristics is important to examine the combustion characteristics of DI (Direct Injection) gasoline engines because the fuel-air mixture formation is controlled by spray characteristics and in-cylinder gas motion. However, the mixture formation process has not been well clarified yet. In this study, the characteristics of a fan-shaped spray caused from a slit-type injector, such as the droplet size, its velocity and the droplet distribution were simultaneously measured on a 2D plane by using improved ILIDS (Interferometric Laser Imaging for Droplet Sizing) method. ILIDS method is an optical measurement technique using interference fringes by illuminating a transparent spherical particles with a coherent laser light. In the measurement of the wall-impinging spray, effects of the distance to the wall and the wall temperature on the spray characteristics were investigated.