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One issue of Homogeneous Charge Compression Ignition (HCCI) engines that should be addressed is to suppress rapid combustion in the high-load region. Supercharging the intake air so as to form a leaner mixture is one way of moderating HCCI combustion. However, the specific effect of supercharging on moderating HCCI combustion and the mechanism involved are not fully understood yet. Therefore, experiments were conducted in this study that were designed to moderate rapid combustion in a test HCCI engine by supercharging the air inducted into the cylinder. The engine was operated under high-load levels in a supercharged state in order to make clear the effect of supercharging on expanding the stable operating region in the high-load range. HCCI combustion was investigated under these conditions by making in-cylinder spectroscopic measurements and by analyzing the exhaust gas using Fourier transform infrared (FT-IR) spectroscopy.

This study examines the effects of ethanol content on engine performances and the knock characteristics in spark ignition gasoline engine under various compression ratio conditions by cylinder pressure analysis, visualization and numerical simulation. The results confirm that increasing the ethanol content provides for greater engine torque and thermal efficiency as a result of the improvement of knock tolerance. It was also confirmed that increasing the compression ratio together with increasing ethanol content is effective to overcome the shortcomings of poor fuel economy caused by the low calorific value of ethanol. Further, the results of one dimensional flame propagation simulation show that ethanol content increase laminar burning velocity. Moreover, the results of visualization by using a bore scope demonstrate that ethanol affects the increase of initial flame propagation speed and thus helps suppress knock.

From the viewpoint of protection of the global environment, reduction of CO2 emissions are high-priority issues for vehicles, along with the demand for increased power performance. One of the more popular technological developments that can help to resolve such incompatible characteristics is the variable valve lift mechanism. Among them, the three-dimensional cam for continuous variable valve lift and timing mechanism has been developed as a technology applicable to motorcycles, because of its small, compact layout and capability of running under high speed engine conditions. The 3-D cam is provided with numerous cam profiles set in an orderly manner and forming a three dimensional map and at points making contact with a spherical roller tappet. An accelerator actuator slides the cam along the camshaft to continuously vary the power output from idling to maximum.

To suppress knock in small gasoline engines, the coolant flow of a single-cylinder engine was improved by using two methods: a multi-dimensional knock prediction method combining a Flamelet model with a simple chemical kinetics model, and a method for predicting combustion chamber wall temperature based on a thermal fluid calculation that coupled the engine coolant and the engine structure (engine head, cylinder block, and head gasket). Through these calculations as well as the measurement of wall temperatures and the analysis of combustion by experiments, the effects of wall temperature distribution and consequent unburnt gas temperature distribution on knock onset timing and location were examined. Furthermore, a study was made to develop a method for cooling the head side, which was more effective to suppress knock: the head gasket shape was modified to change the coolant flow and thereby improve the distribution of wall temperatures on the head side.

Swirl injector spray at high fuel temperatures has unique characteristics [1][2][3][4] compared to normal fuel temperature spray such as strong penetration and narrow spray width. These characteristics have a possibility for improving fuel consumption and exhaust emission at the cold start condition. Thus, Swirl injector spray at high fuel temperature conditions was modeled in a CFD(Computational Fluid Dynamics) code by using a multi components fuel evaporation model and other spray sub-models to predict the mixture formation process at the cold start condition. Results show that, high temperature fuel decreases wall film amount and increases vapor amount. It can be concluded that high temperature fuel has the possibility for improving fuel consumption and exhaust emission at the cold start condtion.