Raised compression and ultra-lean air:fuel ratios are at the core of an innovative combustion control process set to debut here soon. The new SkyActiv-X petrol engine will power flagship additions to the Mazda3 and CX-30 line-ups.

A small displacement Roots-type supercharger assists with the high volume of air needed for ultra-lean combustion.

‘CROSSOVER’ has become a modern automotive buzzword.

Mazda has developed a crossover engine – one which runs on petrol but has combustion characteristics more closely aligned to diesel.

And to emphasise the achievement it’s applied the X-suffix to its SkyActiv nomenclature.

The new 2.0-litre SkyActiv-X delivers the throttle response and revving characteristics of a petrol engine with the high torque and low consumption attributes of a diesel.

It’s a practical application of the Homogeneous Charge Compression Ignition (HCCI) petrol engine principle in which a very lean air:fuel mixture reacts spontaneously to heat and pressure during the compression stroke.

To-date HCCI has been considered impractical for production vehicles because they work in a narrow range of conditions. Variations in atmospheric pressure, temperature and fuel quality can result in destructive pre-ignition and detonation.

Mazda’s clever solution has been to add spark control to an engine that theoretically shouldn’t require a spark plug along with a world-first application of in-cylinder pressure sensors.

The SkyActiv-X engine achieves both spark ignition and compression ignition and can move between modes.

Mazda calls the technology SPark Controlled Compression Ignition (SPCCI). The new engine has a very high 16.3:1 static compression ratio and operates at extremely lean air:fuel mixtures.

The theoretical ideal for gasoline engines is to burn a 14.7:1 air:fuel ratio - known as stoichiometric - which defines that all fuel is burnt without excess air.

SkyActiv-X can operate at ratios more than twice as lean (higher than 30:1) – a scenario in which a spark plug would be unable to ignite the lean mixture.

SkyActiv engine production is now at full steam

In SkyActiv-X the spark plug is used to initiate and control combustion. As the piston is compressing the ultra-lean mixture the engine control systems are monitoring cylinder pressure and combustion is initiated with a small and precisely timed atomised fuel charge being injected close to the spark plug.

When ignited it creates an expanding fireball (Mazda calls this an air piston) that rapidly raises the pressure and temperature in the combustion chamber to the point where the much leaner mixture is ignited.

Mazda says size and timing of the fireball is being constantly altered. At cold start and under high revs/high load conditions the engine primarily works in spark ignition mode.

Across a range of normal driving conditions, it is estimated the engine operates in SPCCI mode about 90 per cent of time.

The extremely lean mixture burns cooler which in turn reduces temperature differences in the cylinder head, piston and cylinder walls. The cooler combustion also significantly reduces the formation of nitrogen oxides (NOx).

Along with less fuel the engine also requires more air for which the solution is a small displacement, belt-driven ‘‘Roots’’ type supercharger.

Mazda's MZ-D Connect centre display provides confirmation of when the SkyActiv-X engine is running in SPCCI mode.

In common with the familiar SkyActiv-G 2.0-litre direct injection petrol unit, the SkyActiv-X measures 1998cc displacement. The engines share much of their block and bore/stroke architecture but a new cylinder head has been designed for SkyActiv-X.

Peak power is 132kW at 6000rpm (compared to the current 2.0-litre SkyActiv-G developing 114kW) along with 224Nm of torque at 3000rpm (up from 200Nm and arriving 1000rpm earlier than current SkyActiv-G engines).

When its powering a six-speed auto Mazda3 hatch on 18-inch alloy wheels the fuel consumption is rated at 5.8L/100km (WLTP test procedure) and Mazda estimates an overall consumption improvement in the region of 15 to 17 per cent along with corresponding CO2 emission improvements.

There’s also a Mild Hybrid contribution to the SkyActiv-X efficiency equation with a belt-driven 24-volt integrated starter/generator system. It assists with engine starting, initial movement away from stationary and bolsters the lower portion of the torque curve.

Hybrid output is rated at 4.8kW of power at 1000rpm with a 60.5Nm torque boost at just 200rpm.

To support the new engine characteristics the gear ratios have been altered. The SPCCI engine doesn’t conform to a normal pattern of increased fuel usage as engine revs increase so shorter gear ratios allow the engine to rev a little higher and provide improved response and a sportier character.

While Mazda has achieved a petrol engine breakthrough with its SkyActiv-X technology, the company says diesel engine vehicles will continue and there is a second generation SkyActiv-D diesel family expected to be announced in the near future.

the Mazda3 (above) and CX-30 are first candidates for this new engine technology.

As NZ introduction nears, it’s timely to remind what a breakthrough this tech potentially represents.

Mazda is now hinting the SkyActiv-X tech won’t restrict to the 2.0-litre engine likely to provision to NZ drivers soon.

“IT is a combustion technology – and that combustion can work on any size of engine, so it doesn’t need to be a 2.0-litre; it can be in other things…”

As New Zealand ramps up to receive our first Mazda vehicles with the brand’s SkyActiv-X engine technology, this comment from the marque’s marketing director in Australia is a good reminder about the full potential of the world’s first production-ready petrol that uses compression ignition.

For now, two models off a common platform have adopted what Hiroshima formally calls it’s SPCCI – for spark plug controlled compression ignition – tech: The Mazda3 and the CX-30 crossover.

Those cars run together in every market where SkyActiv-X places; including in Australia, though there the introductions are staged. The road car first, from this month, and the CX-30 following in September.

Will that double act also provision in New Zealand? All odds favour that outcome, but the local distributor isn’t yet ready to make an announcement. Media have been notified of a conference dedicated to SkyActiv discussion will occur in four weeks’ time.

Anyway, when Mazda Australia staged its press introduction to the cars last week, marketing head Alistair Doak made a good point by reminding that simply because SPCCI – and the mild hybrid involvement it also delivers (more on this in a bit) dubbed Mazda M Hybrid - only packages for now in a 2.0-litre four cylinder form doesn’t mean it cannot reach into other displacements or cylinder counts in the future.

compact crossovers and SUVs are on a sales roll, so a SkyActiv-X provision in the well-received CX-30 is a logical enhancement.

Doak provided the comment that introduces this story as a response to being asked whether the new 2.0-litre four-cylinder could power a vehicle as large as the Mazda CX-9, as an example.

He went on to suggest hinted that Mazda might choose to upscale SkyActiv-X to an engine of larger displacement. But equally true, he suggested, there was no reason the maker couldn’t develop a smaller engine employing the same process.

Which means? Sorry, Doak – doubtless because he is a former motoring writer – was too canny to fall into letting out any secrets in respect to future rollouts.

However, he hinted that the option likely won’t remain the preserve of flagship models in the Mazda3 and CX-30 ranges for long.

Currently, he said, there were no plans to expand SkyActiv-X in other models, “but it’s certainly available to us in Mazda3 and CX-30. It’s available in Europe in those models, across all grades… or most grades…

“So there is that availability… should the desire from customers be there. But ultimately, it’s up to us, from a marketing and brand point of view to tell the story, and explain what SkyActiv is,” he explained.

“If people like that story, and are curious, then hopefully they’ll come and test-drive, and hopefully they’ll buy.

“If the demand is there, then absolutely, we’ll meet that demand. But we haven’t started yet, so it’s very much a hypothetical at this point.”

SkyActiv-X is certainly a new chapter, in that it marks the start of Mazda’s corporate goal to reduce ‘well-to-wheel’ emissions by 50 percent from 2010 to 2030.

It has been in production since last August, and was first revealed to the world in 2018, so you might wonder why it has taken so long to get here.

reduced emissions are a strong plus point with SPCCI.

Coronavirus likely hasn’t been much help but even before that global calamity Mazda had determined to focus first on servicing western Europe, for simple reason that countries there encourage low CO2 engines. The Mazda3 hits that button, if not quite as effectively as a hybrid, with a claimed emission of 127 grams per kilometre.

Sure enough, the make has seen a brisk take-up of the technology in those initial target markets, to the point where the acceptance rate has been much higher than it anticipated.

"Since we launched the engine, we are seeing a very encouraging feedback: 60 percent of the orders for the Mazda3 are currently for cars equipped with the Skyactiv-X engine, as well as 45 percent of orders for the Mazda CX-30 crossover," Mazda Europe CEO Yasuhiro Aoyama said last August. That rate has not decreased since then and the demand has stretched Mazda’s capabilities.

Still, it seems to have now found ability to service our part of the world. Our neighbour reckons it can achieve good supply of the Mazda3, which it takes in manual and automatic formats, and the CX-30, which it will achieve purely in auto. NZ might be even more selective and take just the auto.

SPCCI’s potential to deliver will be eagerly monitored. For one, everyone will be keen to establish the value aspect; a focus that becomes important because this is a premium priced engine, more expensive than the ‘regular’ four cylinders that provision in the two models in 2.0-litre and 2.5-litre formats.

In our neighbour’s case the SkyActiv-X models cost $NZ3300 more than the priciest 2.5s. It’s expected Mazda NZ will do as other markets have and package the powertrain into its plushest trim level, which in this market is called Takami. That’ll be a new fit out for the CX-30, where the current trim line tops with a Limited provision.

As said, SkyActiv-X uses compression ignition typical of a diesel, but with a petrol engine which the brand says helps blend the high-revving character of a petrol engine with the fuel efficiency and torque of an oiler.

Capable of both spark ignition and compression ignition, the engine can utilise the two types of combustion while operating in tandem.

To further maximise fuel efficiency, the engine features an integrated, belt-driven starter generator and 24-volt lithium-ion battery which assists the engine and recoups lost energy during deceleration.

The addition qualifies this to be considered the first hybrid offering in Mazda’s local line-up. Next year, of course, it seems set to deliver its first electric car, with the MX-30.

As explained in previous stories, the attraction of SkyActiv-X is that it presents an intriguing ‘cake and eat it’ proposal – decent pep and yet also potential to deliver very good parsimony.

European numbers show the new 2.0-litre four-cylinder engine will generate 132kW and 224Nm of torque, while fuel economy of 4.3 litres per 100km from the manual is getting close to Toyota Prius levels of efficiency. Be aware that this figure is the result of Mazda using the NEDC testing regime, a format that has now been largely shelved on grounds it’s results are difficult to achieve in everyday driving. Using the now preferred 'real world' (WLTP) fuel economy formula, the claimed consumption is 5.4L/100km.

Still, that thrift and the power outputs place it above the existing 114kW/200Nm 2.0-litre unit and, while the 2.5-litre engine has more punch, with 139kW/252Nm, it also achieves it by using more fuel, 6.6 litres per 100km in an automatic Mazda3 on the test cycle.