Mazda is claiming that its new SKYACTIV-X engine can reduce emissions from an internal combustion engine to a level below that of an electric vehicle when measured from ‘well-to-wheel’.

The Japanese automaker says it is bettering the real-world emissions of EVs by maximising the efficiency of the internal combustion engine through its next-generation SKYACTIV-X petrol engine.

In order to more correctly measure CO₂ emissions over the lifecycle of a vehicle, Mazda is moving beyond current 'Tank-to-Wheel' evaluations (which consider only emissions whilst driving), to a 'Well-to-Wheel' method, which also considers fuel extraction, manufacturing and shipping.

How SKYACTIV-X makes it possible?
Mazda’s new SKYACTIV-X engine comes with the world’s first commercial petrol engine to use compression ignition, where the fuel-air mixture ignites spontaneously when compressed by the piston.

The company’s proprietary combustion method – Spark Controlled Compression Ignition (SPCCI) – combines the spark ignition of a petrol engine with the compression ignition of a diesel. This maximises the operating zone in which the compression ignition is possible and achieves a seamless transition between compression ignition and spark ignition.

SPCCI gives the engine the ability to switch from the ideal stoichiometric 14.7:1 air-to-fuel mixture of a conventional petrol engine to the lean-burn mixture of 29.4:1. This also enables the spark plugs to ignite the mixture in a conventional manner even when the engine is cold or running at high revs.

When the engine is in lean-burn mode -- about 80 percent of the time -- the spark plugs ignite a pulse of fuel-rich mixture injected into the centre of the cylinders under ultra-high pressure during the compression stroke. This, in turn, provokes compression ignition in the pressure and even lets it burn, leading to a more powerful piston stroke.  The combustion timing is controlled by the flame from the spark plug.

Credits: Mazda Australia 

Hence, SPCCI combines the advantages of both petrol and diesel engines to achieve outstanding environmental performance, power and acceleration. Combined with a supercharger to boost intake pressure, compression ignition delivers unprecedented engine response and an increase in torque of 10-30 percent over the current SKYACTIV-G petrol engine, whilst the super lean-burn improves engine efficiency by up to 20-30 percent over the current SKYACTYIV-G. Moreover, SKYACTIV-X is said to even equal or exceed the latest SKYACTIV-D diesel engine in fuel efficiency.

Mazda's reasoning for being on par with EVs
A mid-sized electric car consumes around 20 kilowatt-hours of electricity per 100km. Production of this power with coal translates into CO₂ emissions of 200g/km; with petroleum, 156g/km; and with LNG (liquefied petroleum gas), 100g/km. When converted to a 'Well-to-Wheel' figure, then, the average CO₂ emissions of an EV are some 128g/km, depending on the power generation source, whilst that of a Mazda SKYACTIV-G petrol engine of comparable power is 142g/km. This means that with as little as a 10% improvement in efficiency, SKYACTIV-G engine emissions will be on par with those of electric vehicles.

Mazda’s SKYACTIV-X has won multiple awards across the globe, like the Quattroruote Global Tech Award and the FuturAuto 2018 Trophy for Automotive Innovation.

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