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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.

The Two stroke engines have been around for more than a century and have survived so far, primarily in portable applications. From the beginning, two-stroke engines have suffered from poor fuel economy and high fuel emissions compared to the larger, heavier, but more efficient four stroke designs. Over the last 100 years many innovative ideas have been designed and patented with the intent of improving these two critical shortcomings. Stringent emission regulations introduced in the last two decades have now provided an impetus to revive, revise, and apply technologies to meet these new requirements. With this in mind, many engineers and scientists throughout the world have researched stratified scavenging and injection to make low cost two-stroke engines that will compete with the four-stroke engines.