Technology of the year : BMW Turbosteamer

To reduce greenhouse gas, automotive engineers are working very hard to improve the efficiency of our cars. So far, much of the work has been concentrated on improving combustion efficiency (e.g. direct injection), reducing mechanical loss (e.g. turbocharging), reducing energy consumption of peripherals (e.g. electric power steering and on-demand oil/water pumps) and recapturing energy during braking (e.g. hybrid). But there is one area few people notice: a lot of energy lost through exhaust gas and engine cooling. Last year, BMW unveiled the Turbosteamer technology to recapture this energy.

According to the test results obtained on test bench, the Turbosteamer system can recapture 80% of the energy in exhaust gas and engine cooling system. The energy is then used to drive a steam engine to assist the petrol engine. This boosted 13 horsepower and 15 lbft of torque for the 1.8-liter four-cylinder engine while fuel consumption is reduced by 15 percent. While the development of other green technologies are approaching bottleneck, Turbosteamer previews a very promising future. Moreover, it is compatible with other technologies.

The Turbosteamer employs two close-loop hybraulic circuits to drive the steam engine, one is filled with distilled water and another is filled with Ethanol. The water circuit is the primary, high-temperature circuit (the red loop in picture). It is heated up by exhaust gas at two heat exchangers, boiled to high temperature steam and drive the piston steam engine, which is connected to the crankshaft via belt. The steam is then cooled back to water by the Ethanol circuit at another heat exchanger.

The lower temperature Ethanol circuit (the blue loop) is heated by engine coolant (the green loop) as well as the water circuit (red loop). The lower boiling point of Ethanol enables it to vaporize and drive the second piston of the steam engine. It is then cooled back to liquid state by the radiator. In this way, BMW makes use of the energy which would otherwise lost through exhaust gas and engine cooling to assist the engine. In other words, it is a free lunch.

The Turbosteamer has been designed to fit BMW's production cars. At this stage the hardware is still too heavy (100kg) and too costly for mass production. However, BMW forecasted it can improve the system and reach mass production within the next 10 years.

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