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Mazda’s HCCI engine is a cross between standard gas and diesel systems.

Mazda's HCCI engine blends the best of the standard internal combustion model and a diesel one into a product could revolutionize the auto industry

The engine under the hood of the little Mazda3 is a holy grail of engineering: a gas engine that uses compression, not ignition, to drive the car. That's why there are still only six of them in the world and why it's hurtling me down the autobahn at 175 km/h.

Okay, so the autobahn thing is more for the fun of it, but it's part of the demonstration that Mazda's new Skyactiv-X technology is both practical and realistic. It will be several steps ahead of its current Skyactiv-G technology when it's released in a year or so.

Put simply, a regular gas engine squirts tiny and exact amounts of gasoline into the top of its cylinders, then the pistons compress the air in the area above them and, when the spark plug sparks, the explosion forces the piston down. This is internal combustion – and that downward stroke turns the crankshaft and drives the car.

A diesel engine operates differently: the fuel will ignite with just sheer pressure if you squeeze it hard enough and it doesn't need or use a spark plug. It can be dirty, though and creates additional emissions that must be neutralized with expensive additives.

Mazda’s new SkyActiv-X technology is several steps ahead of its current Skyactiv-G technology.

Mazda's new Homogeneous Charge Compression Ignition (HCCI) engine, however, is a cross between the two. It compresses the air and fuel together so hard that, most of the time, the spark plug is not needed. The gasoline explodes in a fireball when it's squeezed with a 15:1 compression ratio – and the piston is forced down and turns the crank.

Why should you care? Because the HCCI operation is considerably more fuel-efficient while also creating more useable power and fewer emissions. Mazda says the new, cleaner engine will be about 20 per cent more fuel-efficient than the current Skyactiv-G, and will create 10 per cent to 30 per cent more power.

It will be more expensive than a regular engine, though.

Among other things, it needs a costly supercharger to force that much air into the cylinders and additional sensors to monitor the combustion. When it's introduced in 2019, it will be an option at the higher end of the model lineup.

The system is not a true HCCI engine, because it still uses spark plugs that are always sparking. The difference is that the spark is there to make sure the already-ignited fireball is burned as effectively as possible. With this shift in priorities, the explosions taking place above the pistons are far more efficient, needing less fuel – the air-fuel mix can be as lean as 50:1, compared with the usual 14.7:1 ratio of conventional engines.

Confused yet? This is why Mazda let me loose on the city and country roads around its European Research and Development Centre in Germany, to prove the engine will run smoothly, responsively and comparatively cheaply. It did.

Other auto makers, notably General Motors and Nissan, have been noodling away on HCCI engines for years but nobody's got them to work properly yet. The key problems are that the compressed explosions are unpredictable when the engine is too cold or too hot, which is why Mazda kept the spark plugs to regulate everything.

Mazda’s system, while not a true HCCI engine, uses the spark to ensure the ignited fireball is burned as effectively as possible.

The plugs will also ignite the fuel in the conventional way when the engine is too cold or hot to operate properly. On my test drive, a technical readout showed this happened less than 10 per cent of the time – and that included hurtling on the autobahn. My fuel consumption was also improved about 15 per cent over a drive in a current Mazda3 earlier in the day.

None of these solutions to the engineering challenges came easily. Mazda's been working on the new technology for the past two years and hasn't started extreme weather testing yet. Mitsuo Hitomi, Mazda's managing officer in charge of the Technical Research Centre, recalls that he would take a walk every morning to clear his head, and then when he'd return, he'd fire off e-mails of ideas to his general manager, probably 2,000 in all.

He sees this innovation as the logical evolution of the internal combustion engine, perhaps powered eventually by renewable microalgae biofuel, and a viable alternative to electric vehicles. Not every country or region has the hydro supply or clean hydro production to make EVs worthwhile, after all.

"The latest engines, compliant with the latest regulations, don't affect the environment so much. Tokyo, for example, is one of the biggest cities in the world, but it has no air pollution problems," he says.

"All we can do is come up with engines that satisfy regulations and meet people's demands. But when we come up with a new internal combustion engine, some people say, 'Why now? Why bother?' But I believe IC engines can also be effective and we want to get them to be even better."

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