In the midst of recent announcements on “dieselgate” and car companies racing to announce an embrace of engine electrification, Mazda has just done something seemingly rather odd. Its engineers – no strangers to trying novel approaches (rotary engine, anyone?) – have revealed a new powertrain, the Skyactiv-X, which is all about petrol.
Yes, good (or bad) old petrol. Not hybrid, electric, LPG, or even hydrogen. The new engine, coming in 2019, is the “world’s first” to copy diesel motors by using compression to start the combustion process. The “Spark Controlled Compression Ignition” actually operates some of the time as a charge compression ignition engine, but switches to a regular spark-ignition engine when conditions allow it to do so.
What does this mean? In short, diesel fuel economy from a petrol engine. According to Mazda, that means ten to 30 per cent more torque than the current Skyactiv-G engines and, crucially, 20 to 30 per cent more efficiency thanks to the new engine’s “super lean burn”.
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So confident and gung-ho is Mazda, that it claims the Skyactiv-X’s fuel efficiency equals or betters that of its latest Skyactiv-D turbodiesel engine. Now, isn’t that good timing? Just as our love affair with diesel comes to a close, Mazda is coming to the rescue with a petrol option that is supposedly just as economical.
The UK public went diesel mad when they saw how much they could save on fuel costs – secondhand cars with diesel powertrains traditionally commanded £2,000 more than their petrol counterparts, for example – but now things are very different. In January, UK diesel registrations were 4.3 per cent below the year before, while petrol cars were up 8.9 per cent. That once rock-solid price premium commanded by used diesel cars has reduced considerably in the last 12 months, too. All this would have been unthinkable only three years ago.
The reason this compression-ignition approach hasn’t been seen in petrol form before? It’s fiendishly difficult to control exactly when combustion occurs. In regular petrol engines, spark plugs light the fuel at precise intervals; with diesels, injection is used to set the controlled explosion off at the right time.
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With homogeneous charge compression ignition (HCCI), there is no single thing, such as a spark plug, that can control autoignition. Ambient air temperature, air pressure, fuel quality, air-fuel ratio, turbocharger boost, engine speed, engine load and valve timing all come into play and each could affect exactly when combustion happens.
This also explains the “hybrid” nature of the Skyactiv-X, because when Mazda’s new engine can’t keep up with adjusting for all these various parameters, it will have to shun the new-fangled compression ignition system and use traditional spark plugs. This could also mean you only get that “diesel efficiency” on motorways or low-load journeys.
Regardless, this is an interesting development for the internal combustion engine. Throw in the possibility of this technology being linked with hybrid electric systems and fuel efficiency could increase further still. When more car companies follow Volvo’s announcement to commit to electrification of all powertrains (and all will likely have to once the Euro 6D emissions regulations hit in 2019), then the automotive industry will experience a major shift. After all, we’re still in Model T Ford territory when it comes to battery technology, and, in particular, charging technology.
Until we can get to a state where it no longer takes hours to recharge electric cars, there will be a place for internal combustion. That’s obviously good news for the automotive industry, which for myriad legacy, familiarity and economical reasons is unwilling to give up its petrol addiction for some while yet. And, like it or not, Mazda may have just extended its life a little longer.