Mazda is embarking upon what might be its most ambitious modern day engineering change in the Japanese automaker’s history, though it may be easy to dismiss it as any typical and incremental development. It’s SkyActiv-X range of engines, which will power all their cars in the near future, is the first mass produced petrol motor to be capable of diesel-style compression ignition.
They had first announced the plan and general specifications for these engines at last year’s Frankfurt Motor Show, but only now do we see its more tangible manifestations. Congruent with its previous assertions, Mazda’s powertrain division manager Eiji Nakai confirms via Autocar that the new engines do indeed deliver a 20-30% reduction in fuel consumption over an equivalent 2.0-litre unit.
What’s more is that Mazda can now more safely ensure that the cost of producing these new SkyActiv-X engines, which are capable of both compression ignition (termed Spark Controlled Compressed Ignition) and conventional ignition trigged by a spark plug, will cost similarly to that of a conventional petrol or diesel engine today.
While the additional fuel efficiency and reduction in emissions that stem from using compression ignition in petrol engines has been known to the industry for some time now, Mazda’s success in harnessing this for mass production over the abandoned efforts by Mercedes-Benz and General Motors boils down to combining both conventional and compression ignition.
However, this approach was also not without its hurdles, as deciding when to rely on compression ignition and when to invoke the spark plug becomes a very complex decision, and one that the engine management would need to make several thousand times a minute. Instead of choosing one over the other, Mazda elected to have the engine instead switch between a conventional engine’s air to fuel ratio of 14.7:1 and the more lean-burning 29.4:1.
To enable this transition and have it be seamless while at the same time quick enough to respond to the driver’s input for increased power or more fuel economy, Mazda does in fact invoke the spark plug even during high compression cycles, allowing it to ignite an even richer concentration of oxygen and petrol vapour, resulting in more power while keeping the combustion itself leaner (not leaving excess fuel non-or-partially-combusted).
A bevy of sensors will, of course, measure a variety of factors to determine if a conventional combustion (low compression) is needed or that the high compression mode be safe for activation. According to Nakai, detecting these very subtle changes accurately is “very difficult”.
Complicating the equation is Mazda’s decision to introduce supercharging to their small capacity engines to make the in-cylinder ignition mix even more potent, but could led Mazda leapfrog their competitors in power as well as fuel economy, as the naturally aspirated SkyActiv-G range in their smaller cars has so far lacked the kind of oomph that rivals and their turbocharged engines offered.
In its current form, these new generation of engines produce around 140kW and 195Nm - we’re presuming it to displace to 2.0-litres - and could theoretically be tuned to deliver power power and torque without adversely impacting fuel economy or exhaust emissions. The first Mazda to feature this engine is likely to be the all-new Mazda3 hatch due in 2019.
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