Moller International, the developer of the Skycar aircraft, the Rotapower line of Wankel-type rotary engines and the Aerobot line of Unmanned Aerial Vehicles (UAV), has achieved emission levels below California SULEV standards in recent tests of the Rotapower engine fueled by ethanol without exhaust aftertreatment.
The 530cc engine tested produced 22 hp at 4500 rpm with an air/fuel ratio of 20 and lambda of 1.35. The fuel was E95 with 5% acetone added plus a synthetic lubricant together with some castor bean oil. The toxic emission levels with ethanol were as follows:
- Unburned hydrocarbons (HC) = .5 ppm or .0043 gm/hp-hr
- Carbon monoxide (CO) = 9 ppm or .03 gm/hp-hr
- Nitrous oxide (NOx) = 3 ppm or .016 gm/hp-hr
The carbon dioxide produced was 11%—25% lower than with gasoline.
Previous tests of the Rotapower engine using gasoline were witnessed by Dr. Andy Burke from the Institute of Transportation Studies (ITS) at the University of California in Davis. These tests showed that with gasoline the Rotapower engine produced toxic emissions below the ultra low emission vehicle level (ULEV) without using an exhaust aftertreatment (no catalytic converter required).
Moller developed an early version of the Rotapower engine some 20 years ago—based on the rotary snowmobile engine acquired in 1985 from Outboard Marine Corporation—for the Skycar aircraft, a four-person Personal Air Vehicle (PAV) designed for both Vertical Takeoff and Landing Vehicle (VTOL) and high-speed (350 mph) forward flight.
Moller developed a number of enhancements, including a new intake and porting arrangement, a new fuel-injection system, and a proprietary composite coating that reduces fuel consumption and cooling load.
The Rotapower engine is a multi-fuel compatible engine and in testing various fuels including gasoline, diesel, natural gas, and various types of alcohol, Moller found that the engine ran coolest and cleanest on ethanol. Moller has developed a variety of rotary engines from 1.5 to 300 horsepower, and now recommends that they all be run on ethanol when available.
By compounding this engine we are able to supercharge the engine and also add to the power output directly. The effective compression ratio can therefore be increased while the geometric compression ratio is reduced.
NASA has stated after an extensive experimental study of the rotary engine that a compound version of this engine should achieve specific fuel consumption to between .3 and .32 lb/hp hr. This would make the rotary competitive with a turbo-charged diesel, which is the gold standard of engine performance. The high octane rating of ethanol makes it possible to operate at effective compression ratios of 12+ to 1, which tends to offset the lower energy per pound of fuel from ethanol versus gasoline or diesel.
Typically with our Rotapower engine where the rotor is cooled by the incoming fuel/air charge, ethanol gives a 25% boost in power due to the lower charge temperature versus gasoline. Non-compounded versions of our Rotapower engine have fuel consumption about 10 to 15% higher than the best 4-stroke piston when using gasoline. Non-compounded ethanol fueled versions are approximately 5% poorer compared to the best 4-stroke piston engine using ethanol.
Testing is just beginning on our compound engine. We have seen a significant reduction in fuel consumption and exhaust temperature, but it is too early to quote this data without further tests and documentation, which should be available within the next 30 days.—Paul Moller