The concept of a loop scavenged two-stroke engine, controlling the intake and exhaust port by the moving piston, is a proven way to realize a simple and cheap combustion engine. But without any additional control elements for the gas exchange this concept quickly reaches its limits for current emission regulations. In order to fulfil more stringent emission and fuel consumption limits with a two-stroke engine, one of the most important measures is to avoid scavenging losses of fuel and oil. Additionally, it is necessary to follow a lambda = 1 concept for a 3-way exhaust gas after-treatment.
Therefore, using internal mixture preparation systems in combination with different concepts to control the gas exchange process, the two-stroke engine could become a choice for automotive applications, especially as a Range Extender in a Plugin Hybrid Electric Vehicle (PHEV). As various scavenging concepts and several mixture preparation systems can be used for 2-stroke hybrid propulsion, the pros and cons of different concept combinations have to be compared and weighted for an optimum solution.
To get an overview of possible designs for two-stroke engines for automotive applications, this paper presents different concepts for loop- and uniflow-scavenged two-stroke engines with different gas exchange control elements in detail and compares them. Assessment categories for the comparison are, amongst others, the scavenging process, especially the possibility of adjusting the control timing of the intake and exhaust port, the emission and fuel consumption potential, packaging size and so on. Additionally, influencing parameters on the combustion process like charge movement are illustrated. In a final chapter, the system complexity and the thermal and mechanical durability of the different designs are discussed.