Mavinahally, N., Veerathappa, J., Rajgiri, S., and Mavinahalli, V., "Multi-Layer Stratified (MuLS) Two-Stroke Engine," SAE Technical Paper 2012-32-0119, 2012, doi:10.4271/2012-32-0119.
The mandatory emission regulations coupled with market demands have resulted in the development of innovative engine technologies at lower costs for consumer applications. For example, the low cost two-stroke engines for hand-held applications have evolved from high specific output, high emission designs to lower emission engine architectures that meet today's EPA and CARB emission standards. Emissions and fuel consumption have reduced significantly, particularly in non-catalyzed engines. This paper highlights the design features of a Multi-Layered Stratified (MuLS) engine that has demonstrated the ability to meet the current emission standards without the catalyst. The Multi-Layer scavenging system consists of stratified layers of pure air, lean air-fuel mixture, and rich air-fuel mixture that are inducted separately and delivered in sequence into the combustion chamber through ports for minimizing the scavenging loss of the unburned fuel. A 25.4cc production two-stroke engine was modified to demonstrate the proof of the concept.