The most efficient engines in the world are two-stroke diesels. They are used in locomotives and ships where fuel cost is the most important thing. However their peak efficiency (about 50%) is at one power level, which is usually the maximum power. Locomotives solve this problem by having multiple engines and running as many as needed. That way they can have the peak efficiency at any load. Four-stroke diesels are used in trucks and buses. They are not as efficient (about 40%) but have a wide useful power range. Gasoline car engines are less efficient (peak at about 35%) but engineers have improved hybrid car efficiency. Generally hybrids run the engine at its most efficient power level. The Prius operating curve is shown in the first figure. In a hybrid car, the power produced by the engine does not match the power needed by the car. A system of generators, batteries and electric motors accommodate the power mismatch. The gain in using the engine at its peak is greater than the losses in generating, storing and retrieving the electric energy and using it in electric motors. The ideal engine would be efficient over a wide power range. Then the losses in going to/from electric are reduced.
Diesel engines were invented more than 100 years ago. Better designs, materials and manufacturing tolerances have improved efficiency. However these improvements are reaching a point of diminishing return. The YankeeDiesel is a completely new design. The engine extends the peak efficiency over a broad power range by effectively changing size. This is done by changing the size of the combustion chamber while maintaining a constant compression ratio. This is explained in USPTO 8,210,136. A second feature in the YankeeDiesel is a secondary expansion chamber. The combustion gases expand a second time so the engine has higher peak efficiency than today’s best two-stroke engines.
The second figure shows an opposed cylinder arrangement. The crankshaft is between the cylinders and suspended with planetary gears. The crankpins have simultaneous reciprocating and rotary motion. Such a design has nearly continuous net power out from a cylinder pair.
The YankeeDiesel design has stabilized and refinements are becoming small. The third figure shows the eleventh generation model – a four cylinder opposed design with parallel crankshafts. A central shaft is the power takeoff shaft. If the model were a running engine, it would be about 50 hp. The engine will be air cooled and hence lighter than typical diesel engines.
Initial applications would be electric power generation (GenSets) and auxiliary power, such as agricultural pumps. Besides greater efficiency, the engine will be quieter than present diesels. The combustion gases expand a second time within the engine and are released to the environment at a much lower pressure.