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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.

The objective of this study is to develop a practical technique to achieve HCCI operation with wide operation range. To attain this objective, the authors previously proposed the blowdown supercharge (BDSC) system and demonstrated the potential of the BDSC system to extend the high load HCCI operational limit. In this study, experimental works were conducted with focusing on improvement of combustion stability at low load operation and the reduction in cylinder to cylinder variation in ignition timing of multi-cylinder HCCI operation using the BDSC system. The experiments were conducted using a slightly modified production four-cylinder gasoline engine with compression ratio of about 12 at constant engine speed of 1500 rpm. The test fuel used was commercial gasoline which has RON of 91. To improve combustion stability at low load operation, the valve actuation strategy for the BDSC system was newly proposed and experimentally examined.

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.

To clarify the fuel spray formation process for a swirl-type injector, numerical analyses using both VOF (Volume Of Fluid) model and DDM (Discrete Droplet Model) method are carried out. VOF model is used to simulate the two-phase flow inside the injector and also the liquid film formation process outside the nozzle, while DDM is used to simulate a free fuel spray in a constant-volume chamber using initial conditions deduced by empirical equations or calculated results of VOF model. As a result, fairly good agreement of spray characteristics, such as the spray shape and the tip penetration between the experiment and calculation can be obtained by adopting initial conditions calculated by VOF model. However, improvements of droplet breakup models and of two-phase flow calculation method would be required to achieve quantitatively good agreement.

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.

Post-oxidation has been used to enhance the chemical reactions in the exhaust gas pipes, leading to the activations of the turbocharger and catalyst at cold state. In this research, a detailed study of the various mechanisms for post-oxidation is performed. For the post-oxidation activation, the unburned gas species (CO, THC, H2) in the exhaust manifold must be produced by some methodologies, such as scavenging, lambda-split, and post-injection. The required amount of O2 concentration can be either supplied by the scavenging (valve overlap tuning) or the secondary air injection (SAI) system. Mixing the species is also an important key to promoting post- oxidation, and an internal bypass adapter with a modified exhaust adapter shape was developed and evaluated.