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AVL's development of a semi-direct injected two-stroke engine employed a carburetted 250cc production motorcycle engine as a baseline. Special emphasis vas placed on the investigation of fuel jet and scavenge flow interactions. To evaluate the scavenge flow pattern, a steady flow test procedure was developed and applied. The results of scavenging system optimization were confirmed by subsequent engine tests which showed significant gains in power output. Completion of the first phase of the research program resulted in the development of a semi-direct injection system using currently available automotive low pressure manifold injection system components. Compared to the original carburetted engine, significant improvanents were demonstrated, including a 30% reduction of fuel consumption, a reduction of up to 60% in hydrocarbon emissions and up to 70% in carbon monoxide emission, averaged over the engine's speed and load range.

AVL's research program on highly fuel efficient low emission two-stroke engines initiated the development of an advanced cycle simulation program to optimize the intake and exhaust systems and the port timing, as well as the investigation of various fuel or mixture injection systems. The current paper covers the application of the engine simulation program to multi-cylinder engines and presents a summary of the latest test results with the AVL-Direct Mixture Injection System on a 250cc single-cylinder research engine. An analysis of the gas dynamics in the exhaust system of a crankcase scavenged automotive three-cylinder engine is presented and the influence of important dimensions of the exhaust manifold on the pressure wave propagation and on the torque characteristic of the engine is discussed in detail.