A ‘greener,’ cleaner two-stroke engine

Researchers from the Idaho National Engineering and Environmental Laboratory have created a small separator that removes unburned oil and gas from two-cycle engine exhausts without compromising engine performance.

Small gasoline-powered two-stroke engines are used in many applications from recreational motorcraft to hand-held power tools, mopeds, street motorcycles, and even low-cost cars. The engine is popular because it is lightweight, low cost, powerful and exhibits quick throttle response.

An unavoidable feature of the engine is that it requires oil mixed with gas for internal lubrication. During operation, the intake and exhaust ports are momentarily open at the same time, thereby pulling some of the intake stream containing fuel and oil to leak out into the exhaust port, resulting in inefficiency and smoky exhaust emissions.

Typically, 25 percent to 35 percent of the fuel that enters the two-stroke engine leaves unburned. The solution to both problems, according to INEEL researcher and lead engineer Terry Turner, is a technology that can be implemented in new vehicles and retrofitted to existing ones.

The separator takes the exhaust gas and spins it at a high rate, thereby centrifugally separating the heavy oil, fuel and particulates from the lighter gaseous combustion products.

The heavy constituents are burned in an afterburner or captured and removed for recycling or disposal. Turner feels confident that a significant hydrocarbon emission reduction for standard engines, and per unit retail cost under $400, are realistic.

The separator also may reduce noise. Installing the separator inside the existing muffler or exhaust system would be equivalent to adding additional baffling.

‘It’s possible to build an engine with less exhaust, but it will be more expensive and, therefore, less marketable than current designs,’ said Turner. ‘Current manufacturers of two-cycle engines have begun aggressive research in cleaner engines in order to meet the new EPA [US Environmental Protection Agency] guidelines; however, in most cases, the simplicity of the engines is being lost, and in some applications being replaced by lower performance, heavier four-cycle engines.’

The best solution, said Turner, is a separator that can be put to use in new engines and retrofitted to existing ones.

‘The two-stroke engine is a great product with vast applications because of its simplicity and light weight,’ said Tuner. ‘With achievable targets for emission reductions provided by the EPA, it’s now time to provide a workable solution to the emission problems that have plagued the two-stroke engine since it was developed in the 1940s. We feel we have that solution and look forward to moving to the next level of its development.’