By making a petrol work more like a diesel, can the Mazda 3 Skyactiv-X show there’s still life in the internal combustion engine?
This may look like a humble, if rather stylish hatchback, but there’s more to the Mazda 3 Skyactiv-X than meets the eye. Look under its bonnet and you’ll see, well, an awful lot of plastic actually. That’s because its 2.0-litre four-cylinder petrol engine is enclosed in a ‘capsule’ to promote a faster warm-up that improves efficiency.But that’s just the tip of the iceberg, the really clever stuff involves what Mazda calls SPCCI or spark controlled compression ignition. Under light loads, a very lean fuel and air mixture is pushed into the cylinder under a diesel-like 16.3:1 compression ratio on the intake stroke. As the piston squishes everything, a small amount of a richer mixture is squirted near to the spark plug. Igniting this instantly raises pressure so the leaner mixture also ignites, burning cleaner and more efficiently. However, put your foot down and it operates like a regular petrol engine, at least, that’s the theory.To further improve efficiency, there’s also a 24v mild hybrid system that uses a combined starter/generator to harvest energy when you’re slowing down. This can then be used to assist the engine when accelerating from a standstill, for instance. The end result is 178bhp without the use of a turbo, emissions from just 100g/km and official fuel economy of 51.4mpg. That’s rather impressive.Those figures are for the six-speed manual with front wheel drive on 16in wheels. Four-wheel drive and an automatic gearbox are optional, while higher trims receive 18in wheels. Naturally, all these items make the 3 less efficient, with emissions rising to as high as 125g/km.
Source: Autocar
