Even though combustion engines that use pistons and cylinders have been around for almost a century and a half, inventors and engineers are still coming up with new versions that improve efficiency and burn a wider range of fuels. Some of these new engines may not be practical or economical, but it’s difficult to know that without building one first.
Here are several new approaches, or at least variations on earlier efforts, that offer a twist on conventional internal combustion engines (ICEs). And although it is unlikely they will be embraced by major automotive builders — they have their own engine modification programs and efforts — there are rumors of deals with Asian companies making small cars, scooters, and self-powered equipment such as generators and lawn mowers.
The Cyclone engine
The Cyclone engine from Cyclone Power Technologies, Pompano Beach, Fla., is an external-combustion steam engine that can be powered by heat from practically any source, including biodiesel and syngas, according to the company. It is the basis for a new 10-kW auxiliary power unit being built for the Defense Dept. and the U.S. Army Tank Command, where it could see service on the M1 Abrams tank, IAV Stryker, and Bradley Fighting Vehicle.
The engine uses the Rankine Cycle and regenerative external combustion, a combination the company calls a Schoell Cycle engine.
Four basic processes take place inside the engine:
Heat process: Atomized fuel injected into the centrifugal combustion chamber mixes with air and is ignited. Thermocouples control combustion duration to keep heat in the chamber at a constant temperature. The heat then swirls around the heat coils. Water in those coils becomes superheated steam (up to 1,200°F) and gets piped to the cylinders through an adjustable valve. Valve timing determines how much steam enters the cylinders, which controls torque and acceleration.
Mechanical process: Steam enters each of six radially configured cylinders under pressures as high as 3,200 psi, pushing down each piston in sequence. Water acts as the working fluid and lubricant — there is no engine oil. The pistons’ motion drives a spider bearing to turn the crankshaft. According to the manufacturer, torque is greatest on the first rotation of the shaft, so it can be connected directly to the drivetrain without a transmission. In fact, a 38-in.3 Cyclone engine develops over 850 lb-ft of starting torque.
Cooling process: Steam exits the cylinders through exhaust ports and enters a condenser that turns it back to a liquid, which collects in a sealed pan at the bottom of the condenser. Blowers spin fresh air around the condenser to speed cooling. Because this is a closed-loop subsystem, water need not be replaced.
Regenerative process: Air heated by the condenser travels to a heat exchanger where it preheats air coming into the combustion chamber. A high-pressure pump transfers water from the condenser pan to the heat coils via heat exchangers around each cylinder, then to the center of the coils to begin the heat cycle again.
This design yields several advantages, including:
All-fuel capability: Fuel burns in an external-combustion chamber under atmospheric conditions to create steam and power the engine. This lets the engine burn fuels derived from orange peels, palm and cottonseed oils, algae, used motor oil, and fryer grease, as well as propane, butane, natural gas, gasoline, and even powdered coal. In fact, the engine can even run on waste heat from ovens or furnaces, as well as solar collectors.
Environmentally friendly: The engines burn fuel longer than traditional ICEs, which means fewer carbon emissions. At the same time, burn temperatures are lower, below the point at which harmful NOx gases are created. No oil is used, so there is no oil to change, dispose of, or potentially leak. And the exhaust is virtually silent, unlike ICEs, which emit supersonic sound waves into the air.
Efficiency: By keeping heat losses to a minimum, the Cyclone’s fuel efficiencies are on par with top diesel engines. It also has a power density of about 2.5 hp/in.3, far more than traditional ICEs, which put out about 1.5 hp/in.3
Low cost: The Cyclone engine doesn’t need a catalytic converter or muffler, nor an oil pump or oil, and requires no transmission. With fewer parts, the engines is less expensive to manufacture and assemble. And parts can be made of inexpensive, nonexotic materials. The company predicts, therefore, that the engine will cost less than traditional gas or diesel engines of comparable power.
The company is currently developing at least five versions of the Cyclone engine ranging from 5 to 330 hp. They can be used for portable or auxiliary power, automotive or marine propulsion, powering heavy-duty equipment, or scavenging waste heat.
The Grail engine looks much like a traditional two-stroke engine, but incorporates some weight-saving refinements that make it less expensive to manufacture. And its inventors at Grail Engine Technologies, Chapman, Kans., have only been working on it for about two years.
Like other two-stroke designs, this compact engine has a reed-valve intake and alternating combustion and exhaust strokes. The way it runs, however is a bit different.
During operation, the piston travels up and creates negative pressure below it, pulling air in through the carbon-fiber reed valve. When the piston is then forced down by combustion, the reed valve closes. The piston continues down, compressing air in the crankcase chamber and forcing it through an oil-separating loop at the bottom of the piston. Then, when crankcase pressure exceeds the combustion-chamber pressure, the reed valve opens, forcing air through a hole in the center of the piston. This pushes exhaust air out and pulls fresh air in. As the piston moves up, the intake and overhead exhaust valves close, fuel is injected, and the mix is ignited by a spark plug.
With the piston and combustion chamber constantly exposed to cool air moving through the center of their masses, fuel can be injected at anytime without it instantly igniting, and this cuts down on NOx. The engine can burn almost anything as fuel. And it is light for its power output; a 25-lb engine puts out 5 hp, while a 40-lb engine generates 100 hp. The engine is inexpensive to manufacture with many parts being made using simple castings. And the modular design lets it be scaled up by daisy-chaining single-piston engines onto a single crankshaft to make a multicylinder, in-line engine.
Doyle Rotary engine
This engine, the brain child of inventor/engineer Lonny Doyle and owner of Doyle’s Fabrication and Repair in Red Oak, Tex., is a split-cycle engine with one bank of radially configured cylinders handling intake and compression and another similar bank of cylinders for power and exhaust. Both banks encircle the crankshaft. Combustion takes place in a single combustion chamber inside the central crankshaft. This permits engineers to design intake and power cylinders differently for the best performance. The crankshafts also contains air intake and exhaust ports, fuel injection, and a spark plug.
The cylinders, along the cylinder case, spin around the crankshaft when the engine runs, each making one stroke per revolution. Having only one combustion chamber makes for consistent power from each cylinder. So the engine runs smoother and has more consistent wear on components than traditional ICEs.
The engines use far fewer parts — no valve train, for example — and the cylinder case is aluminum, so rotational mass is much less than in a conventional ICE. (A 4.3-liter Doyle engine would have an estimated 75 lb of rotating weight, while a similar ICE would have at least 125.) The Doyle engine is also smaller with less total weight. Inside the engine, fuel burns more completely, which takes place in both the combustion chamber and power cylinders. This cuts down on NOx emissions.
On the downside, the integrity of the ports used to control what goes in and out of the cylinders relies on oil-based seals. This oil inevitably gets burned, creating hydrocarbon emissions. Doyle hopes to develop a better seal that eliminates oil. Still, oil (or possibly water) may be needed to keep the engine cool.
Gerald Kashmerick, after finding out he generates more emissions mowing his lawn then he does on a 2,500-mile road trip, decided to devise a better utility engine, one that could be used for lawn-care equipment, small generators, and other relatively small (10 to 40-hp) machines. While he was at it, he wanted the engine to burn a range of fuels. Eventually he founded Kashmerick Engine Systems in Brookfield, Wis., and came up with the K6, a six-cycle engine.
The key to the K6 is that one cylinder/ piston takes in and compresses the air, which then goes to a combustion chamber in the cylinder head where fuel is injected and the mix is burned. All cylinders in the engine share this chamber, although the current prototype is currently a single-cylinder design. Half of this expanding volume of gas returns to the original cylinder for power and exhaust. Shortly thereafter — after another revolution of the crankshaft — the rest of the pressurized mix goes into the same cylinder for another power and exhaust stroke. This lets the combustion chamber hold several compressed-gas charges, so its size can be adjusted depending on engine size.
Being a six-cycle engine means its should have only two-thirds the power of a four-stroke engine, but the K6 has other potential advantages. With fuel being burned in essentially a high-pressure furnace, there is more time for combustion to take place, which lowers emissions and lets it burn a wide variety of fuels. Kashmerick admits there are still complicated technical problems to be solved, nonetheless, the DoD has shown interest.
Engineers at Pinnacle Engines, San Carlos, Calif., have refined an engine concept first used on World War II aircraft: the opposed-piston engine. The four-cycle engine has a pair of pistons sharing a cylinder. This eliminates half the ignition and injection components, as well as the cylinder head. Instead, sleeve valves let fuel and air in and exhaust gases out. The company says their engines uses the Cleeve Cycle, which lets them run it as an Otto cycle (constant-volume combustion) or Diesel cycle (constant-pressure combustion), depending on conditions and fuel. The engine is said to be 30 to 50% more fuel efficient than traditional ICEs.
The engine can be adjusted, letting pistons in the same cylinders act independently rather than symmetrically. This allows for a range of compression ratios and profiles. The engine can also be directly injected and turbocharged. It can burn a variety of fuels, including gasoline, CNG, LPG, and alcohol fuels. And the engine can be easily scaled up by adding or subtracting cylinders.
Pinnacle has been working with venture capitalists to secure funding for further development. It has also inked a deal with an Asian company to supply engines for scooters that should go into production next year.