Thermodynamic Analysis and Optimization of Two-Stroke Gasoline Engines

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. For an alternative blower scavenged engine configuration the influence of the blower match on the engine performance is investigated as wall as the effect of a variable port timing on the torque curve.

In case that direct injection systems employing compressed cylinder gas to premix and evaporate the fuel are considered, the high pressure cycle is obviously influenced by the characteristics of the injection system. Some important results of a detailed parametric study on this problem are presented and interpreted. Finally, the paper presents a summary of engine test results with the AVL-Direct Mixture Injection System, which demonstrate the anticipated advantages of this system with respect to low hydrocarbon emissions, stable engine operation and excellent fuel consumption.