TOKYO -- Toyota Motor Corp. pitches its new Mirai hydrogen fuel cell car as a godsend for the planet. Heat and water are its only byproducts, not climate-altering carbon dioxide.
But just how clean is that exhaust water vapor? After all, there is artesian spring, pristine mountain stream water. Then there’s bottom-of-the-barrel Love Canal water.
Turns out, the Mirai’s exhaust water is safer than milk, Toyota says.
“We tested the health impact of drinking the water in a special lab,” said Seiji Mizuno, general manager in charge of designing the car’s fuel stack power generator. “They said that compared to drinking milk, this drainage water has much fewer organic impurities.”
Still, the company doesn’t recommend drinking it. That’s because the water is created by sucking in oxygen from the surrounding air and bonding it to hydrogen from the fuel tank.
E. coli and astronauts
“Depending on the place you are driving, some parts of the world might have certain issues, such as organisms like E. coli, which could be hazardous to your health,” Mizuno said.
“You never know what the quality of the air intake is,” he added.
Despite the stack’s high-tech chemical process, it neither sterilizes nor distills the water.
Yet in most cases, teetotaling would be an abundance of caution, engineers said. Indeed, astronauts have generated their own drinking water from fuel cells since the days of the Apollo missions, said Yasuhiro Nonobe, general manager of the Mirai’s overall fuel cell system.
There also don’t seem to be issues with metals or other chemicals from the drivetrain itself leaching into the water. Only in extreme cases might some chemicals bond to the fuel cell’s catalyst and leach into the exhaust vapor, Nonobe reckoned.
Case in point: Sulfur discharged during a large volcanic eruption might cling to the catalyst. “But we’re talking about a massive amount of sulfur,” Nonobe said.
The Mirai emits 37 liters (10 gallons) of water if driven its maximum range of 650 kilometers (404 miles). That is 0.05 liters per kilometer (0.08 liters per mile, 0.02 gallons per mile).
It might be tempting to think of these cars as rolling steam baths. Imagine sitting in a traffic jam of these vapor-emitting cars on a humid summer day in a place like Atlanta.
But in reality, conventional gasoline engines emit just as much water vapor in their exhaust, Nonobe said. So there would be little net change to the overall amount of water released into the atmosphere from a wholesale switch to hydrogen from gasoline, he said.
And the vapor from a gasoline engine is much hotter. That’s because the typical combustion engine operates at a higher temperature than the fuel stack.