FIRST DRIVE: Mazda’s new Skyactiv-X technology

Skyactiv-X brings diesel performance and efficiency to gasoline engines

Published: September 6, 2017, 10:05 AM
Updated: October 11, 2021, 10:02 AM

Mazda Skyactiv-X technology

FRANKFURT, GERMANY – For years, various car companies have been working away at a new kind of internal combustion engine but with little success. The ‘Homogenous Charge Compression Ignition’ (HCCI) engine sounds great in theory but just hasn’t come together in practice.

Mazda, however, believes it has found the elusive solution and plans to include an HCCI engine in its 2019 line-up. The new engine will generate up to 30% more power while using up to 20% less fuel than the brand’s already impressive Skyactiv-G engine. And its tailpipe emissions will also be considerably cleaner.

It will all be part of a new suite of technology that Mazda calls Skyactiv-X.


The theory is fairly simple. A conventional gasoline-powered four-stroke engine uses spark plugs to ignite the fuel in its cylinders, creating explosions that force the pistons downwards, which turn the crankshaft to drive the car. A conventional diesel-powered engine ignites its fuel by sheer force of pressure, but its emissions are dirtier and it needs expensive treatments to clean the gasses that leave through the tailpipe.

An HCCI engine is theoretically the best of both worlds, using higher pressure to ignite the gasoline, like a diesel, but creating fewer emissions. Its major challenge is that it only runs well once it’s reached optimal temperature. If it’s too cold – when first started – it will misfire; if it’s too hot – from driving at high speeds or under heavy load – it will become unstable.

Mazda’s solution is to include a spark plug in the top of each cylinder, but its spark does not ignite the fuel in normal operation. Rather, it produces a fireball within the already-ignited fuel, created by the pressure of the engine’s 15:1 compression ratio, to help it burn more effectively and more cleanly.

In this way, the air-fuel mixture can be as lean as 50:1, which is remarkable compared to the conventional ratio of 14.7:1. When needed, however, the spark can ignite the fuel and the engine can run as a conventional unit.

Sensors in each cylinder monitor the explosions. They constantly adjust the air-fuel ratio and the rate of sparking to ensure the engine runs smoothly, while a supercharger forces extra air into the cylinder to help create the super-lean ratio. This means the engine will be more costly to produce than a conventional unit, and will be offered as an option on Mazda’s higher-end levels of trim.

Does it all work?

I drove a Mazda3 with the new Skyactiv-X technology on the roads here, near the company’s European research and development centre, to put it all to the test. The car was a mule unit, painted flat-black and equipped with few of the comforts of a production vehicle, but it was smooth to drive and responsive to my inputs.

The mule was built on Mazda’s next-generation platform, which is more rigid thanks to a more developed use of “ring structure” at various places of potential flexibility in the frame. It’s quieter, thanks to better insulating materials and understanding of sound, and its seats are more supportive, keeping the spine in the S-shape that’s most effective for comfort. Its suspension is also more sophisticated, constantly adjusting the shock absorbers to smooth out the ride.

I didn’t really notice any of this, of course; I just drove the car around the city and then out into the country, as if I was on a normal drive in Canada. (That similarity was lost on the autobahn, of course, where I floored the throttle and drove at 175 km/h just for the fun of it.) At all times, the little Mazda3 felt like a regular car: it accelerated and braked like any competent compact, and it didn’t throw me around on the curves. Just as well, really – there were no airbags fitted, and there are only six of Mazda’s HCCI engines in existence.

At the end of it all, a readout from the car’s computer compared my drive to a similar drive I made earlier that day in a regular, current Mazda3. It showed my average fuel consumption was improved by about 15% (even though there was no autobahn on the earlier drive), and that the spark plug needed to actually ignite the fuel less than 10% of the time. 

All this has taken Mazda about two years to develop and there’s still further testing needed to fine-tune everything – extreme weather testing in hot and cold climates is next on the calendar – but the company is confident Skyactiv-X will be ready for production in its 2019 model-year vehicles.

Alternative to electric

It’s all part of a larger plan by Mazda to provide the most suitable car to different regions of the world. Its management is cynical of the overall value of electric cars, since many regions create their electricity by burning coal or oil. There are plenty of rural places where the supply just doesn’t exist to keep enough electric cars charged, and the grid will be severely strapped in many towns, too. As well, it’s an enormous challenge to provide practical charging spots for even a small percentage of all the cars in the world.

That said, Mazda is preparing to introduce its first Battery Electric Vehicle in 2019 and a Plug-in Hybrid Electric Vehicle a couple of years after that. Executives here would speak little of them – they see them as no cleaner in the long run for most of the world. In fact, they consider them just a needed response to governments preparing to force the sale of electric cars, and other lawmakers who want to prohibit entirely the future sale of conventionally-powered vehicles. 

Whatever may happen in the next several decades, there’s no doubt the internal combustion engine is still the most practical and least expensive source of power for any car. It’s also possible that future engines may be able to run on another liquid fuel that’s plentiful and renewable: Mazda is working with researchers in Hiroshima to develop a new biofuel made from microalgae that might one day replace gasoline, perhaps as soon as 2040.

For now, Mazda’s betting its new Skyactiv-X vehicles might help persuade both the public and government regulators that internal combustion engines can also be clean and frugal to run. If that includes a little driving fun as well, even keeping pace on the autobahn, then so much the better.