Driving Sports

“The rumors of the rotary engine’s demise have been greatly exaggerated,” stated Jeremy Barnes, Director of Communications for Mazda North America, during a recent interview with our sister-publication, Rotary Speed Magazine. 

Why in this time of high gas prices and heightened environmental concern is Mazda so bullish on the future of what is, by modern standards, a not-so-environmentally-friendly engine? In looking at alternate fuels, it discovered that the rotary design works well burning hydrogen. But, where many other companies are looking to hydrogen to power complex and expensive fuel cell electric cars, Mazda is taking a more pragmatic route by focusing on using the gas as an internal combustion application.  

Through its research dating back to the original Concept HR-X in 1991, Mazda discovered that the rotary motor was uniquely suited for burning hydrogen. Why? Whereas traditional piston motors are insanely hot in the shared injection and combustion area, those chambers are separated in a rotary. This keeps the injection area cool – a critical feature when running on hydrogen. Given the low flashpoint of hydrogen (in other words, it blows up at a lower temperature), controlling the timing of the combustion cycle is critical. You simply can’t have it blow up whenever it feels like it, or the motor won’t last very long. 

Since the rotary engine itself wouldn’t need significant changes to its design, the same powerplant could run on dinosaur fuel as well. All that would be needed would be a separate tank for each fuel type – a dual-fuel system – along with a valve so the driver could choose which tank to run from. This is good for the short-term since, according to the National Hydrogen Association, there are currently only 61 hydrogen stations across the entire United States – many only accessible for commercial use only.

Mazda’s Concept RX-8 Hydrogen RE has been running on such a dual-fuel system since it was first introduced in 2004. Commuting? Reduce emissions running on hydrogen. Ready to have some fun on backroads? Switch to petrol for more power. 

We asked Mr. Barnes why, with so many other manufacturers focusing on hydrogen in fuel cell electric systems, Mazda would focus on burning hydrogen instead of developing a fuel cell. “Fuel cells are massively expensive. It’s not just building the cell, it also means building a complete electric vehicle as well, making costs considerably higher.” He continued, “From a cost and benefit perspective we think it’s better to focus on internal combustion hydrogen.”

One reason Toyota, Honda and GM are pursuing fuel cell technology is that, when it works, it ultimately can produce a vehicle that is much more efficient in converting energy into motion. According to the National Hydrogen Association, traditional fuel vehicles are only 20-percent efficient, hydrogen combustion vehicles – such as the type pursued by Mazda – are better, reaching 25-percent efficiency, but fuel cells take the cake, with a whopping 60-percent efficiency. But at what cost? All hydrogen cars, even the ones that combust hydrogen, produce 0g/km of CO2. And that’s important when considering ultimate impact on the planet, but if it requires a second mortgage just to fill up with a tank of the wonder-juice, that will certainly play its part in overall adoption. 

Though it’s not making as much news as the latest advances in fuel cells, Mazda isn’t alone in pursuing the hydrogen combustion model. In 2007 BMW introduced its Hydrogen 7, a hydrogen internal combustion version of – you guessed it – its 7-series executive saloon. But, unlike the diminutive 1.3-liter rotary, the BMW was toting a massive 12-cylinder powerplant adapted to run on liquid hydrogen in an otherwise similar dual-fuel setup as Mazda’s RX-8 Hydrogen RE. The result is a 260-hp car that gets a reported 17 mpg on traditional fuel, and less than 5 mpg running on liquid hydrogen. This is, naturally, a massively complex system that relies on super-cooling the hydrogen in the tank, to keep it in a liquid state.

It’s hard to figure out where Mazda’s latest hydrogen rotary squares against the behemoth Bimmer, since no one at Mazda was able to provide us with apples-to-apples consumption data. Mazda’s latest concept is based on a Mazda5 and sports both the dual-fuel system as well as a new hybrid powertrain. This concept, called the Premacy Hyrogen RE Hybrid, has a maximum range of 124 miles on hydrogen from its pressurized 35-megapascal (MPa) tank (5,000 psi).  This is touted as being a 40-percent improvement over the original RX-8 RE concept. 

Compared to fuel cell cars, such as the Honda FCX Clarity (just now becoming available to lease in Southern California for a limited number of customers, mostly celebrities) the glimmer of internal combustion hydrogen starts to loose its luster. Honda’s “production ready” sedan garners a claimed equivalent of 68 mpg with a similarly pressurized hydrogen tank as the Premacy RE, with a total range of 280 miles. If we take the leap of logic that the Premacy RE has a similarly sized tank (physically, they seem to be about the same size) then we could speculate that the Premacy RE is running – at best – in the territory of 30 mpg on hydrogen. This would be supported by the efficiency data provided to us by the National Hydrogen Association. Now, consider that the new Europe-only MINI Cooper D gets up to 76 European mpg (or 53 mpg when “driven hard” according to a recent review in the London Times) on low-sulfur diesel, and has less than half the emissions (104g/km) of the current RX-8. If such mileage and emissions are do-able with standard fuels, why bother with hydrogen at all?

Considering the pending climate crisis, it’s important to reduce CO2 emissions wherever possible. Though cars aren’t the only contributor to the phenomenon, they certainly are doing their part to wreak havoc on our ecosystem. Take a look at the current 2008 RX-8: it produces up to 284g/km of CO2. For comparison, the Nissan 350Z with its V6 scores a similar 280g/km and the Toyota Prius, when running on its little assist motor, generates 104g/km of CO2. Outright elimination of the CO2 emission would be a great step. But that’s the trade-off at the end of the day: expensive and complex fuel cell versus relatively simple hydrogen combustion. Mazda is placing its current bet on the latter, since it takes advantage of current production technology. Sure, not as whiz-bang as fuel cells, but even burning hydrogen still yields only water vapor as the only relevant emission. 

But all this cheering for hydrogen ignores a very important fact: there is currently no single source for hydrogen large enough to power an entire city of cars, let alone an entire country. It may be the most abundant gas in the universe, and it certainly has done a great job keeping our Sun lit, but it’s not like we can drill it out of the ground. Actor Jamie Lee Curtis can be happy that she’s not contributing to global warming by driving her Honda FCX Clarity, but what she’s really done is merely moved the “problem” from her own back yard to someone else’s. Yes, Virginia, fossil fuels are used to produce hydrogen. Currently the most common way to produce hydrogen is by fancy processing of different forms of fossil energy sources: natural gas and coal being two of them. Some companies are working with electrolysis of water, which doesn’t produce harmful emissions in the process, but this is extremely expensive and takes far more energy to produce than what is stored in the hydrogen it creates.

That doesn’t put the hydrogen economy at a complete dead end: Even today, Iceland is already using geothermal power to produce hydrogen. But the fact remains that for mass adoption there will have to be a number of breakthroughs in the near future to bring down the cost and emissions related to its production, storage and use. It’s a classic case of cart before the horse. 

Starting in the spring of 2009, Mazda is making a couple hundred of its Premacy RE Hydrogen vehicles available through dealers in Japan, as development of the hydrogen rotary continues. Is a hydrogen-powered rotary the future of transportation or a dead-end? Only time will tell, but Mazda is optimistic about its future as part of the “hydrogen economy.” Until that utopia arrives, and hydrogen can be produced efficiently and cheaply, it seems as though these wonder cars will be relegated to limited-production R&D vehicles and the driveways of image-conscious movie stars.

Photos courtesy of Mazda and Honda.