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The following is from Roundel, BMW's magazine. It is, of course, slanted to all things BMW are good but I found it interesting.
With gasoline prices spiraling through the roof, carmakers around the globe are scrambling to make their cars more efficient. Most of these efforts are focused solely on improving fuel economy with hybrid technology using two power trains, mostly gasoline and electric, usually at some sacrifice of performance. But BMW is taking a different approach by creating ways to reduce fuel consumption-while at the same time increasing performance. That approach called Efficient Dynamics, has led to an innovative concept that uses a car's largest but as yet untapped source of energy: heat.
BMW Turbosteamer technology uses heat from exhaust gasses and engine coolant to generate steam which provides additional horsepower to the engine. Classified as a thermodynamic hybrid, the system slashes fuel consumption by 15% and generates an additional ten horsepower and fifteen foot pounds of torque when installed on a four-cylinder 1.8 liter Valvetronic gasoline-powered engine.
Development on Turbosteamer began in 2000 at BMW Forschung and Technik (Research and Technology), an engineering skunk works established in the '80s best known for the futuristic Z1 roadster, the three-seater Z13 concept car-with a central driver's seat similar to the McLaren F1's seating configuration-and the E1 and E2 electric-powered concept cars.
PUTTING EXHAUST GASSES TO WORK
The high temperature circuit, which harnesses exhaust heat, is the primary source of the steam. A pump pushes water into two reservoirs, one positioned close to the engine and the other taking the place of the primary muffler, producing between 145 and 730 psi, depending on the amount of heat available. Even under partial engine loads, heat from the exhaust warms the water to 1,022F, the resulting steam then flows into an "expander machine" that has a connecting rod directly linked to the crankshaft-similar to a steam locomotive-to provide more power to the engine.
During this process, the steam cools to 300-390F. The residual steam is pumped into a heat exchanger, which works as a compressor, and then into the secondary circuit. The high-temperature circuit captures 80% of the energy contained in the exhaust that otherwise would escape through the tailpipe.
HARVESTING HEAT FROM ENGINE COOLANT
Residual exhaust heat and heat from the engine coolant provide the energy for the low-temperature circuit to create steam by heating ethanol. Ethanol is used here because it has a lower boiling point than water (160F). The ethanol is moved around the circuit by a pump at 44psi and is warmed to 220F; however, this temperature is not enough to drive the second expansion machine , requiring an additional loop to the end of the exhaust heat exchanger, which provides enough energy to heat the ethanol to 300F. The resulting steame is directed into the expander machine. A conventional radiator channels unused heat to the air.
Because Turbosteamer is a closed system, the water and ethanol do not need to be replenished.
THE NEXT STEPS
Current development work is centered on making the components lighter and more efficient (currently each circuit weighs about 110 pounds). The system already fits in a current 3 series with minor modifications.
Turbosteamer is most effective with a gasoline engine (also referred to by engineers as an "Otto-cycle engine" after Nicolas Otto, who, along with Eugen Langen, invented the four-stroke-cycle gasoline engine in 1865), but it is also suitable for use in diesel engines. Howerver, since power losses are not as great in diesel engines, the amount of recaptured energy will be less.
Researchers say that a 20% reduction in fuel consumption is about the limit of the system, and that it is most efficient on long trips. They estimate the Turbosteamer can be ready for production within 10 years.
BMW has not said whether a steam whistle will be part of the package, but it would be a nice touch.
Some days it's hardly worth chewing through the restraints
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