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Honda Reheats The Steam Hybrid Concept

February 27, 2008

BMW Turbosteamer EngineHonda is examining ways to capture and recycle waste heat energy. The company is currently examining the potential of the Rankine cycle, a closed thermodynamic cycle that converts external heat to work. According to the company’s preliminary results, the Rankine cycle can regenerate three times as much energy as a regenerative braking system can.

The Honda Rankine system uses the vehicle’s waste heat to generate steam. A high-pressure water pump forces water into a modified catalytic converter with an integrated evaporator. Using heat from the catalytic converter, the evaporator turns the water into steam. The steam is shunted to a volumetric expander, where it powers a generator, and the resulting electricity is stored in the vehicle’s on-board battery pack.

To test the impact of the Rankine cycle, Honda modified a production Stream crossover, which is sold in Japan and Europe. The unmodified vehicle uses a 2.0L direct injection gasoline engine. The company outfitted the test vehicle with the Rankine system, and added a steam control system to regulate the temperature and pressure of the steam. The control system enables the Rankine system to respond to changes in the load on the engine, and can optimize the performance of the system based on driving conditions.

Overall, the modifications on the test vehicle showed that the volumetric expander can generate as much as 43 hp, although the maximum thermal efficiency of the unit is 13% at 30 hp.

Honda isn’t ready to commit to the technology for production vehicles yet. The company wants to see higher efficiencies before considering this for the mass market.

In 2005, BMW developed the Turbosteamer, a steam-based power generation system, which recaptures waste heat from the vehicle’s coolant system and engine exhaust to heat water in a closed reservoir to 550°C. An expander converts the pressure into mechanical energy and transfers the power to the crankshaft. According to BMW, about 80 percent of a vehicle’s waste heat energy could be recycled into usable power.

BMW’s version of the “Turbosteamer” steam hybrid provided an additional 14-hp and an overall improvement in efficiency of 15 percent. The Turbosteamer includes a second heat capture system that uses ethanol in place of water and operates at a temperature of 100° C- 150° C. The second system also dumps its recaptured energy into the vehicle’s powertrain and adds a modest 10 kW of power. The Turbosteamer works best with gasoline engines. Reduced emissions from diesel engines means that less heat can be recaptured and recycled.

At the time of its development, BMW planned to make the modifications universally available on all of its existing and future models, but did not expect to have a production version of the technology ready until about 2015. Additionally, the prototype system added 220 pounds to the test vehicle, which was unacceptable when considering the measured efficiency gains.

Written by Hybrid Car Chat · Filed Under Hybrid Technology 

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