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Mazda wants to perfect the internal combustion engine before we give it up

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The SkyActiv-X engines will set the path for electrification

Image: Mazda

One thing that sticks out about Mazda is their frugality. Their cars are about less being more — less weight, fewer cylinders, more space efficiency inside. Some of this is actually a necessity because, in the great scheme of the global auto industry, Mazda is a small company. They still have the occasional tie-up with Ford or Toyota, but Mazda mostly develops cars by itself. While it sounds like the company is making life difficult for itself, it can at least stick to its core belief that cars are all about driving.

“We love cars and want people to enjoy fulfilling lives through cars,” says Masashi Otsuka, vice president of R&D and design for Mazda North America.

But what does that look like in an increasingly electrified and automated world? Mazda isn’t exactly buying into the rush for plug-ins and self-driving technology. In fact, it’s doubling down on the internal combustion engine. Yes, even after governments spent much of last year pushing for legislation to make all new cars electrified and other automakers gave into the push, Mazda announced its plans to make its gasoline and diesel engines even more efficient than they are today with the release of the SkyActiv-X engine and the promise of diesel-like economy with vastly better emissions.

Even Mazda’s engineers can’t believe they’re on the path to perfecting this for a launch late next year (final tuning for refinement and various global emissions regulations still have to be worked out). But the company is close to solving most of the energy inefficiencies of the combustion engine without diminishing performance or adding the heavy batteries or complex transmissions rivals have introduced.

The story behind the SkyActiv-X engine (it’s “X,” not “ten,” for the record) is the so-called Spark Controlled Compression Ignition. It’s mission is to balance performance and economy in not just sports cars, but an everyday compact hatchback like the Mazda 3. That means it also has to operate smoothly so the driver doesn’t notice what the tech under the hood is doing to achieve that balance.

Gasoline engines have spark plugs to ignite the air and fuel mixture to combust and make the engine operate. Diesels use compression ignition, which forces air and fuel to combust without a spark, improving efficiency but resulting in higher emissions. And compression ignition engines also suffer in terms of refinement compared to spark ignition cars, Mazda engineers say, which they think would turn off prospective drivers who aren’t as swayed by fuel economy claims as others.

“In general, higher compression means higher efficiency and more torque,” says Dave Coleman, manager of vehicle dynamics engineering for Mazda North America. “But tune it to avoid knock and the gains go away. It’s diminishing returns.”

That’s why Mazda’s system essentially has three modes of operation. The first operates much like a conventional gasoline engine with direct injection, using a spark plug to ignite the fuel mix and a little supercharger to more forcefully get air in there. Once the car’s started and warmed up a little, however, the second mode engages a lean-burn strategy in a more efficient mode that can be used when accelerating or in normal driving. But a third, ultra-lean mode kicks in to achieve peak efficiency, with the spark plug managing the compression ignition so the driver doesn’t notice what’s happening under the hood.

And perhaps the most notable thing about the SkyActiv-X engine was that its operation went unnoticed. We drove prototype versions of the engine, paired to manual and automatic transmissions, in modified versions of a current Mazda 3 hatchback around the company’s North American technical center in Irvine, California. While the bodies are based on the current 3, Mazda said largely everything we couldn’t see is off of the new 3, due to go on sale next year.

Engineers stuck an iPad on the dash where the infotainment screen would normally be to show which mode we were in. The most efficient mode was usually achieved around 40 mph and at 3,000 rpm. It’s a narrow band, for sure, but light pressure on the accelerator pedal kept it in that third mode during numerous city driving situations. But the experience was much like driving the already fun-to-drive Mazda 3, but with a more solid, more VW-like feel thanks to the new platform’s stiffer structure and more comfortable seat. And the engine’s changing modes were largely imperceptible, something Mazda’s engineers are no doubt proud of in the pursuit of producing a homogeneous charge compression ignition engine.

“Conventional HCCI combustion has a very limited range of application. A practical engine needs to operate in dual modes which means that it still needs a spark plug,” Mazda powertrain engineer Jay Chen says. “In order to operate in the real world, an HCCI engine needs to smoothly switch to normal gasoline spark ignition combustion.”

And that may have doomed efforts by General Motors and Hyundai to market such technology.

“About two years ago, we finally made the realization ... we need the spark plug inside the engine anyway,” Chen says. “Why don’t we used the spark plug to control when the compression ignition operates?”

This 2.0-liter four-cylinder prototype engine has a 16:1 compression ratio and has been designed to run on 87 octane regular unleaded. Like the current SkyActiv engine in Mazda’s products, it’s meant to be a modular design, although the company wouldn’t give details about future sizes or cylinder counts. At the Frankfurt Motor Show last fall, Mazda estimated the engine would produce 187 horsepower, up considerably from the 155-horsepower figure on the current 2.0-liter SkyActiv engine in the US. The company has targeted a fuel economy bump of between 20 and 30 percent with this new engine, too, which would put it well into the 40-50 highway mpg ballpark compared to a current Mazda 3 2.0’s EPA ratings.

It’s also designed to work with Mazda’s upcoming hybrid and plug-in hybrid models, due early next decade. The company calls the prototype engine a “mild hybrid,” but wouldn’t say whether it had a 48-volt electrical architecture. Engineers did say, however, that it would incorporate a start-stop system. Either way, the SkyActiv-X is designed to work with future electrified efforts and cooperate with Mazda’s pledge to make its semi-autonomous driving system standard on all its vehicles by 2025.

There are still hurdles to get SkyActiv-X certified and refined by the 2019 target, and the company quietly acknowledges it won’t replace the current engines overnight, meaning it will likely be an option on the upcoming Mazda 3, at least at first. There are also some cost considerations weighing on accountants.

But the prototype drive was promising and it accomplishes much of what Mazda vows to do: to get the internal combustion engine as perfected as possible in terms of efficiency and operation before jumping head-first into an electric future.

“In the future, when we electrify cars, all of these improvements go along forward,” Coleman says. “It’s an investment in that future.”