Is Mazda’s SKYACTIV-X petrol engine cleaner than current EVs?


As car manufacturers of the world focus on hybrid and electric solutions, Mazda has opted to further develop their SKYACTIV-X petrol and diesel strategies.

The motor world is at a major crossroads. Globally, governments are looking at the possibility of banning diesel engines in their cities. Ireland recently announced that from 2030 no more diesel or petrol cars would be sold in our country. Even the media has bought into the whole “diesel is dead” campaign. All of a sudden we all think that we are experts in CO2 emissions and NOx, and many think that the only answer to these problems is the mass production of electric vehicles.

For the most part I do think that this makes sense. I mean, drive an electric vehicle and while you’re at the wheel going through cities and fidgeting with range anxiety, you are at that moment creating zero CO2 or NOx emissions.

Mazda are asking us to start thinking in a “well-to-wheel” way.  But what does “well-to-wheel” mean?

Here’s my way of explaining it. When you physically drive a petrol or diesel car, this is the only time that your vehicle burns CO2 and NOx emissions. When you physically drive an electric vehicle, you burn zero emissions. “Well-to-wheel” asks you to think about the amount of CO2 and NOx emissions burned while you are actually charging your electric car.

You see, you have to think about what’s creating the power that drives an electric vehicle. Where does that energy come from? In many instances, that power comes from fossil fuels being burned at the power plant, and therefore, while you may not actually be burning CO2 while you are driving, your car is actually responsible for some of these gases in our atmosphere.

“Well-to-wheel” is a great way to think if you are currently considering an electric vehicle purchase – especially if the reason for an EV purchase is on account of environmental benefits. For some reason, a lot of us have bought into only half of the reasoning behind EVs. We look at the fact that you can drive one and burn no CO2 or NOx. The other half of it is to ask ourselves from where the energy that powers our cars comes. If the power that charges into our cars comes from wind energy or hydro energy, then yes, your EV probably makes more environmental sense than a petrol or diesel engine, but if that energy comes from fossil fuels, then you should do a little more homework.

Mazda have done their own math on this subject and by their reckoning, EVs are nearly as toxic as traditional combustion engines. Here’s the breakdown according to Mazda;

  • Two thirds of the world’s electricity is currently produced using fossil fuels
  • A mid-sized EV consumes circa 20kw of power per 100km
  • Production of this power with coal emits CO2 emissions of circa 200g/km
  • Including the use of non-fossil fuel energy sources, the “well to wheel” average emissions of an EV can be worked out as 128g/km.
  • Mazda’s SKYACTIV-G petrol engine currently emits 142g/km from tank to wheel.

Based on these figures, an electric vehicle burns an average of 128g/CO2 using the “well-to-wheel” theory. A SKYACTIV-G Mazda petrol engine currently burns 142g/km. In theory, if Mazda could lower that figure by as much as 10%, then they would technically be as “green” as an electric vehicle. This is what Mazda has decided to focus on.

Here’s where their newest technologies come in. Mazda are currently working on what’s called SKYACTIV-X engines. Yep, it’s a fancy name and it sounds like a superhero from the Avengers – but even at this stage (they’re still developing it), it produces improved efficiency over the current SKYACTIV-G engines by between 20-30%. In fact, test results show that SKYACTIV-X matches or exceeds Mazda’s diesel engines (SKYACTIV-D) for fuel efficiency. These engines aren’t in production yet, in fact they are currently working off six prototype engines in Mazda3 models. We’ve been told that they should be ready to hit the market in 2019.

SKYACTIV-X petrol engines are different to traditional petrol engines in the way that they seem to have borrowed some of the workings of conventional diesel engines. Mazda has designed a new method for delivering fuel to a car’s engine. They call this method “Spark-Controlled Compression Ignition” or SPCCI for short. It combines the spark ignition of a traditional petrol engine with the compression ignition of a diesel. Without going into the science of it, which is available to read here, it effectively changes the air-to-fuel ratio which is used in normal petrol engines. This means that it uses leaner amounts of petrol and more air to power the engine. When the car is cold or running at high revs, it ignites the spark plugs in a conventional manner. However, when the engine is warmed up (which is about 80% of the time) it goes into lean-burn mode. Counter to what I was expecting, this actually increases performance and torque delivery to the vehicle – but at the same time it is more fuel efficient and burns less CO2.

Mazda’s SKYACTIV-X technology is exceptionally good. However, I think Mazda are facing an uphill battle here. A lot of the world has bought into the theory that EVs are far cleaner than petrol or diesel cars. If you use the “well-to-wheel” theory, this won’t be entirely true until the world starts using less fossil fuels to create the electricity that powers our cars. Mazda’s battle is to convince punters that this is the case – but they’ll have to get the message through all of the noise that is being made by media and global governments regarding the switch to EVs.

While I was test driving the new engine in Portugal last week, Mazda Europe’s CEO, Jeff Guyton, introduced another elephant into the room. He announced that by 2020 they will be introducing a new generation of their SKYACTIV-D diesel engines to the fold. This is going to have be a very green engine to put a halt to governments like our own contemplating bans on diesel. Governments don’t like back-tracking, and they hate the taste of humble pie.

Recently the Irish Government unveiled their Project Ireland 2040 strategy and in it they tell us that by 2030 no more diesel or petrol engines will be sold in Ireland, and by 2045 no NCT is to be carried out on internal combustion engine cars. While Project Ireland does have a focus on renewable energy, will the ratio of sustainable energy sourced be enough to mean that the use of electric vehicles actually makes more sense?

Mazda hasn’t completely given up on electric vehicles. In fact, the company has said that they will introduce mild hybrid technology or microhybridisation in 2019. In 2020, they will have models with built-in batteries and a plug-in hybrid for 2021. They’ve formed an Alliance with Toyota, Subaru, Daihatsu, Hino and battery manufacturer Denso, to explore the development of EVs. So SKYACTIV-X and their second generation SKYACTIV-D engines appear to be a stop gap until the world figures out how to completely reduce or eradicate “well-to-wheel” emissions.


About Author

Daragh Ó Tuama

Daragh is Contributing Editor and founder of Past and present motoring ventures include presenting MotorMouth on Newstalk 106-108FM and MPH on TG4. Daragh was also editor for Car Buyers Guide and contributor for He set up the motors section on and can be heard regularly on Rónán Beo @3 on Raidió na Gaeltachta. He’s a regular contributor to The Sunday World’s Motor Mouth pages and he also regularly contributes motoring content for the Irish language online magazine,

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