Fresh on the heels of last week's tie-up with Toyota, Mazda announced on Tuesday that it has finally made a breakthrough in gasoline engine technology. Mazda is calling it Skyactive-X; we know it better as homogeneous charge compression ignition, or HCCI. It should mean a 20- to 30-percent boost in efficiency compared to Mazda's current gasoline direct-injection engines, and we may well see it in the next revision to the Mazda 3.

HCCI engines have been one of those "if only" technologies for some time now. Kyle Niemeyer first covered the idea back in 2012 for Ars as part of a deep dive into new engine tech that could help meet looming efficiency requirements for automakers.

In essence, HCCI is an attempt to run a gasoline engine like a diesel instead. Rather than squirt fuel into a cylinder—done directly, at high pressure, in the case of Mazda's current gasoline engines—then ignite it with a spark, the fuel and air are well-mixed and then compressed to achieve the bang in suck, squeeze, bang, blow.

Because the fuel and air are so well-mixed, combustion should happen simultaneously at multiple points within the cylinder's volume, burning more evenly, at a lower temperature, with fewer particulates or nitrogen oxides in the exhaust than a normal spark-ignited gasoline engine or a diesel engine. Making it work is apparently much harder than describing it; at various times, General Motors, Volkswagen, Mercedes-Benz, Ford, Honda, and Bosch have all tried their hand at the technology to little avail.

But Mazda is nothing if not stubborn when it comes to eclectic engine technologies; after all, it bravely persevered with the rotary engine for decades. In January, there were signs that it had made real progress with HCCI, and today we have the confirmation as part of a broader announcement from Mazda about its new long-term sustainability plan. Another element of the plan—given the catchy title "Sustainable Zoom-Zoom 2030"—is to start introducing EVs and hybrids "in regions that use a high ratio of clean energy for power generation or restrict certain vehicles to reduce air pollution."

This engine still has spark plugs!

The new HCCI engines will still use the good-old spark plug; for some operating conditions, it's better to run it as a conventional spark-ignition engine. Mazda says it has perfected the control issues that let the engine know when to transition between spark ignition and when things can be leaned-out enough to use HCCI, and it's calling it "spark controlled compression ignition."

The engines will also be supercharged, so they will be torquier than the current Mazda gasoline-powered engine range, and they'll be cleaner and more efficient. (Mazda's press release says that, volume for volume, they should be comparable to its current turbodiesel range in that regard.)

Reuters reports that Mazda also plans to keep HCCI to itself, although we wonder if that applies to its new best friend Toyota.

We know there is a vocal population who would like to see OEMs like Mazda give up development of new internal combustion engine technology altogether, focusing instead on fully switching over to battery electric vehicles. These days, national governments are throwing out dates like 2030 and 2040 for banning new fossil-fueled vehicles from sale.

But 2040 is a ways off, and if William Gibson has taught us anything, it's that the future is not evenly distributed. Certainly in the mid-term, there will be a use for hydrocarbon-fueled vehicles, particularly outside of dense urban corridors where average journeys are shorter and recharging infrastructure is thicker on the ground. So anything that makes those vehicles cleaner and more efficient ought to be viewed as a good thing.