Combustion Analysis on Piston Cavity Shape of a Gasoline Direct Injection Engine

This paper describes the analyses to improve both stratified and homogeneous charge combustion of a gasoline direct injection engine. In this study, computational fluid dynamics (CFD) and high-speed hydrocarbon (HC) measurement were employed to observe the mixture formation process. The analysis of the combustion flame propagation was conducted by in-cylinder visualization and ion current measurement. As a result of the analyses, the following conclusions were made:

1. 1
   An oval shaped wall cavity can direct the mixture gas to the vicinity of the spark plug better than a conventional shell-shaped wall cavity. The oval shaped wall cavity can improve fuel consumption and HC emission at stratified charge combustion.
2. 2
   A shallow cavity improves the homogenization of mixture gases and wide open throttle (WOT) performance. In addition, the depth of the piston cavity effects the combustion speed of the homogeneous charge operation.
3. 3
   The cavity depth has an optimized value that balances stratified and homogeneous charge combustion.

As a result of this study, a shallow cavity piston with an oval shaped wall was developed. It achieved low fuel consumption, low HC emission, and high WOT performance.