Combustion Analysis with Residual Gas as a Design Parameter for Two-Stroke Engines

In a variaty of applications, two-stroke engines assert their usage as a propulsion unit, for examples in off-road vehicles, scooters, hand-held power tools and others. The outstanding power to weight ratio is the key advantage for two-stroke engines. Furthermore, two-stroke engines convince with high durability and low maintenance demand. However, an increasing environmental awareness, the protection of health and the shortage of fossil resources are the driving factors to further enhance the internal combustion process of two- stroke engines. The reduction of emissions and fuel consump- tion with a constant power level is focused on.
Developments deal with the optimization of the combus- tion process itself or the enhancement of the exhaust gas after- treatment. Especially in very small two-stroke engines an exhaust gas aftertreatment system is rarely applied, due to disadvantages regarding component temperatures and product costs. Beside different parameters, the exhaust gas back pressure mainly influences the residual gas content as well as the gas exchange in two stroke engines. Both are essen- tial for the combustion process quality, which can be deter- mined by values of 50% MFB, COV, glow ignition and knock behavior. Additionally, scavenging losses and the volumetric efficiency vary in dependency of exhaust gas back pressure. The emission level is significantly affected by these values. To gain deeper insights into these engine specific connections, a wide operation range concerning equivalence ratio (rich and lean) as well as ignition timing of a two-stroke engine is analyzed. The aim of research is to declare the limits of the combustion and gas exchange process with respect to the residual gas content. From this, possible optimizations can be derived. To gain knowledge about the combustion specific relations with the focus on residual gas, an approach is presented, which gives an opportunity to estimate the residual gas content inside the combustion chamber for two- stroke engines.