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Mazda is set to buck the trend toward higher octane fuel with its next-generation SkyActiv petrol engines, but will the federal government thwart its effectiveness?
Set to appear first with the fourth-generation Mazda3 in 2019, the new SkyActiv-X engine's effectiveness actually depends on pre-detonation or knocking, which higher octane petrols like 94 RON E10, 105 RON E85 and 95 RON and 98 RON Premium have been designed to resist.
Speaking with CarsGuide at Mazda's 2017 Global Tech Forum in Germany last week, SkyActiv-X technical research and control system boss Mitsuo Hitomi confirmed that in its ideal guise, the engine's ability to combust petrol through compression ignition will require Regular 91 RON fuel, and any higher octane rating will force the engine to revert to pure spark plug ignition like a conventional engine.
In this ideal guise, the new engine will use a combination of spark plugs, compression ignition and supercharging to deliver claimed real-world efficiency comparable to a conventional diesel engine - or 20-30 per cent better than an existing Mazda petrol engine, with torque boosted by 10-30 per cent.
Asked whether the new engine will be able to handle towing as well as current models, Hitomi-san confidently suggested there will be no compromise.
Branded by Mazda as SPCCI, or Spark Controlled Compression Ignition, the world-first technology bucks the recent trend toward lower-capacity turbocharged petrol engines which tend to use higher octane fuel to deliver impressive fuel consumption and emissions figures - as stated via windscreen stickers on every new car sold in Australia.
Such engines can stray significantly from their claimed efficiency figures in the real world however, while Mazda claims SkyActiv-X is more stable through load and climate variations. So highway driving vs city, winter driving vs summer for example.
Regular 91 RON fuel has traditionally been the standard petrol option in Australia, but the emergence of cheaper E10 ethanol-blended fuel, two different grades of Premium and the predominantly ethanol E85 has meant that good old 91 RON is often hard to find at the pump.
Prices can vary considerably among the petrol types, with the average cost in Sydney this week of E10 at $1.30.4, Regular 91 at $1.30.9, Premium 95 and 98 at $1.44.6 and $1.51.6 respectively, and E85 at $1.36.5 according to fuelcheck.nsw.gov.au app.
Considering the average distance travelled by Australian motorists of 13,716km per year (according to abs.gov.au), and based on the current Mazda3 2.0-litre auto hatch's 5.8L/100km official combined figure, coupled with the fact that the new engine is tipped to be up to 30 per cent more efficient and less susceptible to fluctuations in heavy traffic, SkyActiv-X tech should deliver genuine savings.
Based on these figures, choosing between a 91 RON Regular Mazda and the 95 RON Premium required by many other current models could mean a difference of over $400 each year.
So Mazda's 91-preferring SkyActiv-X sounds like a big win for Australia, but such a victory could be stymied by a federal governmment proposal to ban the sale of 91 RON by 2020. This was one of five scenarios proposed to update existing fuel standards in a discussion paper in December 2016.
Hitomi-san suggested a partial solution is planned for markets like Europe where 91 RON fuel is scarce or unavailable, which would be supplied with engines using a higher 16:1 compression ratio to enable both compression and spark ignition functions to operate. This spec won't deliver quite the same efficiency gains as the 15:1 compression ratio version delivered to 91 RON-using markets such as Australia, however. For context, international versions of the existing SkyActiv petrol engine feature world-leading 14:1 compression ratio, while Australian and US models come with a still-impressive 13:1 ratio.
Hitomi-san explained that the ability to measure near-infinite parameters through advances in computer technology is the number one factor that will enable Mazda to produce such a system, with the SkyActiv-X ECU using dual-core processing and a 24 Volt electrical system instead of the usual 12 Volt setup. Also key is the pressure sensor required to accurately measure cylinder pressure during the compression cycle and quickly respond to changing conditions in what is a highly volatile combustion process.
Despite the accuracy required for the SPCCI process, Hitomi-san explained the SkyActiv-X engine will use conventional spark plugs in lieu of expensive bespoke parts, and that recommended service intervals will be no more frequent than existing models. The suggested oil will be no more exotic than that specified for conventional turbos, and the engine will continue to use a timing chain instead of a belt requiring regular replacement.
Asked whether the new engine will be able to handle towing as well as current models, Hitomi-san confidently suggested there will be no compromise and efficiency will not taper as sharply under load as with existing petrols.
He also assured that the system has been designed to start reliably from temperatures as low as -30 degrees Celsius, but the engine will use spark ignition until it reaches operating temperature.
The SkyActiv-X prototypes we drove were all 2.0-litre units, but Hitomi suggested that a range of capacity options is planned.
The supercharger used is a conventional Roots type, which Hitomi-san said was chosen over other designs - including a turbo and the Miller-cycle supercharger previously used in Eunos models - because of its instantaneous boost delivery and breadth of efficiency.
The announcement of SkyActiv-X tech comes barely a year after Mazda's return to turbocharged petrol technology with the CX-9's 2.5-litre engine, but Hitomi-san assures the brand isn't necessarily moving away from the turbo. Instead, he can see turbos being the solution for high performance models in the future. When asked if this could include the upcoming rotary-engined vehicle, Hitomi responded "of course." Watch that space.
Hitomi-san expects markets with tightening CO2 emissions regulations like Europe to see SkyActiv-X engines phased into their model line-ups soon after the 2019 Mazda3's appearance. Cost-driven markets like Australia will likely see the new engines fitted to top-spec models first, with the mainstream trim levels continuing with updated versions of the existing SkyActiv engines.
The SkyActiv-X prototypes we drove at the Global Tech Forum last week were all 2.0-litre units, but Hitomi suggested a similar range of capacity options to the existing petrol line-up is planned.
Mazda has been working toward a compression ignition solution for petrol engines for some time, and the technology is also expected to appear in the reborn rotary engine for the brand's 100th birthday in 2020.