You could be forgiven for thinking all cars in the future will be electric. But chances are there will still be diversity when it comes to automotive propulsion systems. That's because engineers are constantly tweaking the efficiency of the internal combustion engine; turbochargers, superchargers, variable valve timing, direct fuel injection and other tricks all increase efficiency and power by a few percentage points each.

But what manufacturers really want is to increase efficiency by double digits. One technology that offers this promise, and that manufacturers have been chasing for a while is HCCI, or Homogeneous Charge Compression Ignition. GM, Mercedes, Nissan, Lotus and others have all been working on it, but none have perfected it enough to get it to market. Mazda, however, has just announced that they have.

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HCCI is a technology by which fuel and air are compressed in an engine's cylinders to such a high density that the mixture spontaneously combusts--no spark plug necessary--driving the piston into its power stroke. Diesel engines work this way, and the higher compression ratio of diesel is what literally gives it more bang for the buck. (Higher compression = more power when the fuel mixture ignites.) The downside with diesel is that it creates dirty fumes, requiring expensive post-exhaust systems to prevent the car behind it from being covered in soot.

To achieve HCCI with conventional fuel is a tricky matter. First off the engine has to be beefed up, as with a diesel engine, to ensure the greater power expended in each power stroke doesn't blow the darn thing apart. Secondly you need a way to, amidst changing conditions, consistently control the compression and combustion so that it occurs precisely when you want it to, absent the precision of a spark plug.

Mazda says they have figured this out with their new Skyactiv-X engines. Unsurprisingly they're not saying how they did it, but they reckon the new technology increases efficiency by a staggering 20% to 30%, while increasing torque by 10% to 30%. They're also saying that the Skyactiv-X, which is supercharged, "even equals or exceeds the latest SKYACTIV-D diesel engine in fuel efficiency."

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The Skyactiv-X technology, which they're calling "Spark Controlled Compression Ignition" (the engine will still contain spark plugs, to be used in certain conditions) is due to be rolled out with Mazda's model-year 2019 cars. 

Internal combustion engines, it seems, are going to hang around for a while.