Last year a collaborative effort in Britain of Lotus Engineering, Jaguar and Queen’s University Belfast began developing a two-stroke engine called Omnivore, for its ability to run on a variety of fuels. The direct-injection engine has the ability to vary its compression ratio from 8:1 to 40:1 by changing the volume of the combustion chamber. On Dec. 9, Lotus released test results that it termed successful for fuel economy and exhaust emissions.

Image A two-stroke engine designed by EcoMotors.

And in Chapman, Kan., impressively credentialed scientists, engineers and investors are developing what they call the Grail Engine, a reference to their quest for a power plant beyond current levels of efficiency and greenness.

The Grail Engine differs from two-stroke convention in the use of an intake valve positioned in the top of the piston to admit the fresh charge of air for combustion. It also has an overhead exhaust valve, surrounded by three spark plugs, and a fuel injector at the top of the combustion chamber. The project’s goals are to exceed 100 miles per gallon and 100 horsepower from a clean-burning 1-liter engine. While there is no running prototype, interest in its approach has brought a visit by research engineers from Honda Motor.

In simplest terms, the strength of the two-stroke engine lies in its delivery of a power pulse with every revolution of the crankshaft; the familiar four-stroke piston engine in today’s cars fires each cylinder on every other revolution.

Both types of engines use a four-step combustion cycle that converts fuel and air to power: intake, compression, ignition and exhaust. But the two-stroke does it all with just two sweeps of the piston through the cylinder, one up and one down. The four-stroke design takes twice as many trips of the piston up and down the cylinder, allowing more time for each step and placing less stress on the engine.