A new mode of internal combustion engine – called homogeneous charge compression ignition (HCCI) – has a potential to improve fuel efficiency while producing significantly lower NOx emission. So far, most HCCI engine research has been focused on larger engines suitable for automobiles, and very little research has been conducted on the potential of smaller scale HCCI engines. In a related previous study with a 25cc air-cooled engine, several problems were identified while operating in HCCI mode due to its physical dimension and geometry. This thesis uses a water-cooled, 49cc engine with a higher compression ratio to improve HCCI operation.

In this study an engine test facility is constructed and characterized. The engine’s power output, coolant temperature, fuel consumption rates, and emission characteristics are measured. In addition, the results of the characterization tests provide clear directions for operation of the small engine in HCCI. Along with the experimental effort, a transient finite difference method heat transfer model is implemented to estimate the likely HCCI operation regime with this engine. The model’s prediction agrees well with the experimental data from the 25cc engine. Moreover, the model suggests that increasing the intake temperature is an easier way to operate the engine in HCCI than increasing the engine wall temperature. This small scale HCCI research will contribute to improved thermal efficiency and better emission control in small engine applications, where no stringent regulation is in place.