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The main objective of the paper is to describe the optimization work performed to adjust direct injection (DI)-technology to SI-engines running at high (8000 to 10000 rpm.) and extremely high speeds (more than 18000 rpm). In the first category are located a certain number of small and middle displacement two-stroke series produced engines. In the second category are the typical high power racing engines used for competitions like the formula 1. The first part of the paper describes the particular requirements that an in-cylinder fuelling and mixture preparation will have to fulfill with the extremely short period available for introduction and vaporization of the fuel. The paper continues with a description of the different spray shapes, spray penetration velocities and atomization capabilities, which are optimal for the different combustion chamber architectures.

The performance of a small cross-scavenged two stroke spark ingition engines have been analysed by means of a displacement-mixing model for the intake gases, a two-zones combustion model, and one-dimensional numerical technique for the gas flow in the exhaust system. Numerical studies have shown that two stroke engine performance can be optimized by using a resonant chamber connected by means of a valve to the exhaust manifold. The configuration of the exhaust system C the resonant chamber's volume, the geometry of the pipe) may be determined as function of the required engine applications by the implemented code.