Are You Ready for a Fuel Cell Turbocharger? Here's How It Works

Legacy auto industry suppliers of mechanical parts are rushing to establish their seat at the electrification table, and Garrett Motion—global supplier of turbochargers, e-turbos, traction drives, and cooling compressors of all sorts—has carved out a niche producing the primary mechanical component required to make a hydrogen fuel cell operate: the compressor component that supplies its oxygen. Just as in a turbocharged engine, compressed air entering a fuel cell triggers a reaction that releases heat, after which hot exhaust exits. Garrett's third-generation compressor design taps tap that exhaust energy just as a turbocharger does. We recently sat down with Craig Balis, Garrett's Chief Technology Officer, to better understand the similarities and differences between turbocharging a fuel cell and a combustion engine, so here's the break-down.

Similar Form Factor

Both turbocharging applications involve an impellor through which the hot exhaust expands, imparting rotational energy that helps drive a compressor turbine mounted to the same shaft. Of course, in this case there is also an electric motor attached to this shaft that does most of the work.

The exhaust leaving a highly stressed turbocharged engine can easily top 1,800 degrees Fahrenheit. The air and water vapor leaving a fuel cell tops out around 400 Fahrenheit. That simplifies the materials selection task, eliminating the need for high-nickel or other exotic alloys and allowing use of steel and aluminum alloys. Managing the water vapor presents some challenges with erosion of certain materials and components, but the challenges are well understood by now.

20 Percent Energy Savings, No Lag

With a quarter the temperature, there's considerably less energy to tap into. Then again, a fuel cell's compressor doesn't need to work nearly as hard as those in a highly stressed gas four-cylinder turbo. Of course, the fuel cell's job is to provide electricity, and this compressor is typically the second greatest consumer of electricity in a fuel-cell EV after the traction motor, consuming from 10-12kW for the smallest compressors and 25-30kW for heavy-duty applications.

Minimizing such parasitic losses boosts efficiency and extends range, and Garrett reports that adding an exhaust expander "turbo" can reduce the electrical energy draw of the compressor by 20 percent. A driver could never feel "turbo lag" in any production FCEV, because they are all battery-electric "hybrids," which rely on stored energy for instantaneous response. And in any case, the electric compressor spools up instantly, after which exhaust pressure builds, reducing the compressor's electrical load.

Lower Speeds

A typical ICE turbo may spin at 200,000 rpm or faster, while Garrett's biggest fuel-cell compressors top out at about 150,000 revs. While lower than ICE, that's high for an e-compressor, and such speeds help shrink the package size. One complication of the fuel-cell compressor is that its electric motor, a synchronous permanent-magnet type, must spin at the same speed—there's no reduction geartrain involved. That's about 10 times faster than a traction motor spins, and it's too fast for traditional sensors to measure turbine speed and position. Instead, Garrett's sophisticated software algorithms infer this data ten times per revolution based on voltage and current.

Oil-Free Foil Bearings

Trace amounts of oil would poison a fuel-cell membrane, so compressor shafts must rely on "air bearings" that feature an ultra-thin metallic foil that helps generate and maintain a cushion of air pressure between the shaft and housing. No external pressure is applied, it's all generated by the spinning shaft, which "lifts off" as speed builds from a stop and "lands" upon shutdown as it comes to a stop.

No Turbo Whistle

Much of the endearing whistle that identifies most turbos is aerodynamic noise. Every effort is made to eliminate this and all other noises from these compressors, as nothing else makes much noise in a fuel cell. The foil bearings also help reduce noise, and increase longevity—it's said to be good for 1 million start/stop cycles.

Featured in BMW iX5 Hydrogen and More?

Garrett's first-gen fuel cell compressors powered the limited production Honda Clarity FCEV, the second-gen has regular production duty in the few other production fuel-cell vehicles to hit the market, and this third-gen has been confirmed for production in the BMW iX5 Hydrogen. First announced in 2020, the car was presented in Antwerp in March 2023, boasting a range of around 300 miles (WLTP cycle) and refueling in three to four minutes. BMW is now operating pilot fleets in selected markets to gain customer experience. And it won't stop there. Garrett has ongoing relationships with "tens of OEMs" globally, so BMW may not be the first and certainly won't be the last to production with a Garrett Motion fuel cell turbocharger.