This 10-kW auxiliary power unit is a Wankel rotary engine that is 20 in. long and weighs 77 lb. Smaller versions are being developed for use in luxury cars and heavy-duty trucks, while this unit may see use in miniature residential or commercial power grids.
As this cutaway shows, feed water comes in from the upper left, travels through the outlet heat exchanger, and across to the exhaust gas heat exchanger. It then travels through the steam generator, up over the heat cell, and into the injector. The steam is then injected through the superheater unit into the cylinder. Condensed, it returns to the water tank.
The CPSC can burn gasoline, diesel, kerosene, natural gas, alcohol, methane, hydrogen, or other renewable fuels. It does not use an open flame, which drastically reduces emissions of NOx and CO. If any hydrocarbon emissions are produced, they are beyond measurement, says Enginion.
The steam generator is made of thin-wall austenitic steel tubing, and delivers its 500º C charge to the dome-like superheater unit. This element gathers heat from one of the CPSC units, and keeps the steam from cooling during the expansion cycle.
When fuel cell supporters tout the technology's efficiency and cleanliness, they can't help but mention that the only "byproduct" produced is water. Big deal. There's a new engine out there that runs on water. If you haven't guessed by now, it's a steam engine. The company that created this technology is Enginion, a wholly owned subsidiary of IAV, a German engine research and development firm located in Berlin. The engine is called "Ezee", for "Equal Zero Emission Engine." And, says company president Michael Hoetger, "its production price is expected to be equal to or lower than current powertrains."
If this isn't the stuff of fairy tales, consider this: The three cylinder test engine is a two-stroke displacing 1.0 liters, and capable of producing up to 500 NM (400 lb.-ft.) of torque. Oh, and it weighs about 265 lb., can fit under the hood of a compact car, and the combustion technology is adaptable to most any piston or rotary engine architecture.
Central to the Ezee is the Caloric Porous Structure Cell (CPSC), an aluminum oxide-based ceramic heat cell that can theoretically process any fuel that can be vaporized and pre-mixed with air while producing extremely low emissions. The pores of the cell structure are designed in such a way that the fuel is prevented from flaming up, which would produce spikes in emissions of hydrocarbons (HC), carbon monoxide (CO), and nitrous oxides (NOx). Enginion claims HC emissions can't be detected, CO and NOx emissions are well below 10 parts per million, and that the latest cell designs cut these levels by 50%. Adding exhaust gas recirculation reduces them even further.
The even combustion process also keeps the cell at a "moderate" 1200°º C. Enginion says the cell's power output can be varied from 5%-100% of its rated output of 30 MW/m3, and has a response time of just 5 milliseconds. A glow plug is used to start the cell.
However, the thermal cell is only part of the picture. The Ezee test engine uses a modified piston engine design to convert thermal energy into kinetic energy. And, like just about everything else about the Ezee, there's nothing standard about the test engine.
"Ultra vaporized steam" replaces the exploding air/fuel mixture as the work medium in the Ezee engine. Water is fed from a small onboard tank through a heat exchanger, where it picks up waste heat on its way into the steam generator. The steam generator is heated by the exhaust gas from two CPSC heat cells, it turns the water into steam with a temperature of 500°º C and pressure up to 500 bar.
Tightly packed austenitic steel tubes make up the steam generator unit. A total tube length of 200 ft. per cylinder is used, which translates into a heat transfer surface area of 10 ft2. Because the water content of the steam is just 25%, the total mass of the steam is relatively low. This permits the use of thin-wall tubing, which also helps keep engine weight down.
An electronically controlled injection system introduces a precise amount of steam into each of the tubes of the superheater; a dome of nickel-alloy tubes is heated directly by one of the two CPSC cells. This transfers heat to the incoming steam. As the piston travels down, the superheater unit introduces more heat into the cylinder to keep the steam from cooling during the expansion cycle, thus increasing the engine's thermal efficiency.
The injectors are similar to those used in common-rail diesel engines, and are controlled by an electronic module using off-the-shelf components. Says Hoetger, "The Ezee has electronic processing needs similar to a modern internal combustion engine, and injection volume is critical because the engine can generate extremely high torque very quickly." The adaptive electronic control unit's main task is matching injection volume to demand to prevent the delivery of too much power.
No Oil? No Problem!
Oil can't stand up to the temperatures found inside this motor, plus Enginion researchers wanted to avoid the risk of contaminating the engine's sealed water supply. So the decision was made early on to use the steam to both drive and lubricate the engine, and four years were spent researching cylinder liner and piston materials that would match these varying requirements.
The steel cylinder liner is coated with a proprietary composite material, and the piston and its rings are made from carbon composites. Enginion claims the combination has very low friction and wear characteristics, can operate under very hot conditions whether wet or dry, and are recyclable and non-toxic.
The crankcase, on the other hand, sits in a bath of water and polyethylene glycol. The glycol lubricates the main bearings, prevents the water from freezing, and can be separated from the water through heating. Thus any excess water in the crankcase can be fed back into the steam cycle as necessary.
The Defrost Cycle
When the engine is shut off, steam pressure pushes the water out of the engine and back into the insulated water tank. Once the freezing point is reached, a small flame is ignited to keep the temperature in the tank at 5ºº C. This heating mechanism is shut down after several weeks have passed in order to conserve energy, and the water tank has been designed to take the pressure exerted by the freezing water without cracking.
Enginion says it takes an engine 30 seconds to reach maximum power from a cold start, though the car can drive away before then. This compares favorably with the time needed to accomplish a similar task with a diesel engine, though it is far longer than needed to start a cold gasoline engine. The company didn't elaborate on the time necessary to start a "frozen" Ezee engine.
Don't expect the first Ezee engines off the assembly line to go directly into the engine bays of future vehicles, however. Though the concept probably is easier for the uninitiated to understand than fuel cells, there is still much work to be done before it is ready to power automobiles.
"Unquestionably, the Ezee technology would be ideal for vehicle propulsion," says Hoetger, "but it would take about six years before it was application ready." Automakers are keeping tabs on the engine, and developing countries would like to use it to power low-cost commercial vehicles due to its broad fuel requirements and low emission production. However, the company wants to demonstrate the engine's capabilities through extensive static operation first.
More (auxiliary) power!
"Auxiliary power units (APUs) could go into production much earlier than vehicle powertrains," says Enginion vice president Herbert Clemens. "We hope to develop a marketable product by 2004, and have shown a compact unit about the size of 5-gallon water jug that can meet the heat and electrical needs of a large household." A prototype is already running in the company's lab.
This Wankel rotary design weighs approximately 77 lb. and is about 20 in long. Enginion claims it has a maximum noise output of 54dB, and would cost $850 to produce at a production level of 100,000 units per year. Its 10-kW output could heat and light several homes, and by adding networking capabilities to its electronic control unit, Ezee could be joined together to create miniature power grids for residential or commercial use.
A similar unit is under development for use as an APU in automobiles and heavy-duty trucks. "An S-Class Mercedes draws four kilowatts at idle," says Clemens, "but traditional alternators can only produce a maximum of two kW. Even integrated starter-alternators have difficulties satisfying these energy demands due to their size restrictions and dependency on engine speed. A tiny Ezee APU would be sufficient to meet all of these needs."
There is, however, one catch. Enginion doesn't want to build the engine. It would rather stay focused on R&D, and leave the production to someone else. "We would develop Ezee products that are ready for application," says Hoetger. "The production partners would pay a few dollars per unit for the production license, which would allow them to determine their profit margins and distribution channels without any interference from us." Hoetger thinks it will take more than a handful of manufacturers to meet the demand. "All of the studies we have found indicate the potential markets for this technology have a combined volume above $200 billion."