Benefits of the D-Cycle Engine
The Differential-Stroke Cycle Engine (D-Cycle) can double engine driving power, substantially increase gas mileage, and reduce engine-out emissions - all for only a small investment. Unlike the 4-Cycle, the D-Cycle frees the piston from the crank pin, operating it by a separate mechanism to execute the exhaust and intake strokes. This enables independent stroke lengths and timing.
Existing engines can be easily retrofitted with D-cycle pistons and associated modifications. The retrofit willl enable the following:Doubled driving power
By having producing one combustion per revolution in every cylinder, which doubles the torque and power output in the driving range. This is accomplished by freeing the crank/conrod during the Exhaust/Intake stokes. Effectively, the each cylinder in the D-Cycle engine works full-time instead of half the time like in the Traditional 4-cycle. This makes a 4-cylinder D-Cycle drive like a Traditional 8-cylinder.
Substantially improved efficiency
- By assigning intake strokes to the engine's duty cycle,
Current day engines are oversized for typical duty cycle demands, which are only about 1/3 or lower of engine capacity. Traditional engines choke the intake in order to fulfil this power requirement, making it operate away from the performance sweet spot. D-cycle intake strokes are designed to operate the duty cycle at/near the sweet spot, optimizing typical engine operation. The D-cycle retains the original 4-cycle crank arm, producing similar torque per combustion. When needed, the D-Cycle is then supercharged to recover the full load capacity.- By enhancing the gas mileage further by more extended power strokes
The D-cycle power stokes are designed to allow an expansion ratio at around double the compression ratio, producing substantially more power from the same fuel. Combined with sweet-spot operation the gas mileage improvement is estimated as greater than 30%.- By operating at a lower engine speed and/or with fewer cylinders
A traditional engine that has been retrofitted with D-Cycle technology can acheive the same drving power output at only half the RPMs. Lower engine speed yields improved gas mileage due to less frictional losses. Alternatively, a smaller D-Cycle engine operating at a lower speed can also produce the same driving performance with better gas mileage.For example, a D-cycle I-4 running at 2,250 rpm will have the same number of combustions per minute as a traditional 4-cycle V-6 running at 3,000 rpm, while having better gas mileage (frictional losses are approximately proportional to speed squared).
Better engine-out emissions
- Exhaust Gas Retention (EGR)
The D-cycle exhaust stroke can stop short of the TDC to retain some exhaust for emission improvement. The burnt-gas retention reduces or eliminates the troublesome EGR system. BGR cooling can be provided by cooled charge air.- Optimal combustion speed
Optimal combustion speed is about 1000 ft/min while optimal induction speed is approximately double that. Because the piston is tied to the crankshaft in Traditional engines, all strokes must have equal speed, forcing a compromise between these. By freeing the piston from the crank pin, the D-Cycle engine allows differentiated stroke speeds for both combustion and induction, optimizing them for better turbulence and more complete combustion of fuel mixture. This results in better performance and lower emissions.Small investment
The D-Cycle leverages existing traditional 4-cycle engine technology, hardware, and tooling. The only design difference from traditional engines is the piston-train, which is based upon existing valve-train technology. A traditional engine can be easily retrofitted to D-Cycle by replacing its piston with D-Cycle piston-train and gear ratio change (from 2:1 to 1:1). Furthermore, no major changes in tooling or packaging will be required.
For more information, see SAE Paper 970837 - Variable Piston Timing or contact us by mail, email, or in person if you have questions.
