When engines burn fossil fuel NOX is generated and it is extraordinarily tricky to reduce at the tailpipe. Older diesels are being demonised for dirty emissions even if their CO2 is relatively low but petrol engines are quite polluting too. Generally petrol engines produce higher CO2 while also generating NOX albeit not as much as diesel combustion. This is why car makers have had to resort to adding Adblue tanks to the current Euro6 crop of diesel engines to make them emissions compliant. European emission regulations are only going to tighten and innovation is needed. Thankfully Mazda is proving to be the bright spark of the industry with the world’s first commercially available spark controlled compression ignition engine or SPCCI for short.
Mazda has developed in the Skyactiv-X engine a more efficient way of controlling how petrol combusts. Ample power is generated in this case 180hp as opposed to the standard 2 litre Mazda Skyactive-G’s 120hp. Mazda says its new engine can be a sporty driver or an everyday thrifty commuter. The Skyactiv-X uses a very high fuel air mixture of 16.3:1 usually it’s 14.7:1. By carefully controlling when the spark ignites the mixture the X produces power with less heat generation – a key component in NOX generation. By running with greater thermal efficiency less harmful emissions are created. Traditionally a petrol engine uses spark plugs to ignite its highly flammable fuel and create power while a diesel engine ignites its less flammable fuel as a result of the high pressure the fuel is injected in to the engine. Petrol engines are often described as spark ignition engines while diesels are referred to as a compression engines. Mazda with Skyactive-X has married both methods.
Earlier in the summer we tested a pre production Mazda3 Skyactiv-X engine on the roads around Frankfurt. Its power and torque impressed but it did make a slightly odd sound. We have just tested the slightly tweaked production version in Bulgaria that now sounds just like a regular petrol engine. The X is lively and pulls very well. On a mix of motorway and rural roads the handsome Mazda3’s Skyactiv-X proved to be a fun machine to hustle along. Mazda says the new engine is not designed for performance driving alone but as a fuel efficient commuter too. The X delivers the best of both driving worlds as required. To enjoy enthusiastic dynamic performance you need to get the revs up.
Power output figures are good with the 2 litre four cylinder engine making 60hp more than the G engine with the same displacement. The torque figure is very good for a petrol unit at 224nm (213nm G). This pulling power is available from quite low down the engine rev range (3,000rpm). The new engine is quite smooth and responsive. It has a free revving feel that you don’t associate with an economical car. The X can be driven through a conventional automatic or six-speed manual gearbox. The manual gearbox reveals more of the engine’s nature. Hold on to the gears up through the rev range and enthusiastic performance is on tap. The trip computer does however remind the driver that this is not the most economical way to drive endorsing Mazda’s everyday use claim. A period of considered driving allowed our fuel consumption figures dip down in to the mid 4l/100km – close to Mazda’s claim.
The Skyactiv-X also features fuel and emissions saving cylinder on demand technology. Under a light load the car will tip along fueling just two of its four cylinders, when power is needed all four cylinders fire up. With Skyactiv-X the throttle is always open and never closed – allowing better intake of air to the cylinders. Both G and X engines used in the Mazda3 use the latest generation 24 volt ‘M hybrid’ mild hybrid system with integrated belt driven starter/generator. When you lift off the throttle energy is recouped to its small 600kJ lithium-ion battery allow the car run very smoothly. Mazda’s NEDC-2 emissions figures for the Euro6d compliant Skyactiv-X engine state a sub 100g CO2 figure of 96g/km with an average fuel consumption figure of 4.3l/100km (65.6mpg) for a Mazda3 saloon on 16 inch wheels. Mazda Ireland Won’t bring the poverty spec model in and so it lowest quoted CO2 figure is 102g/km NEDC-2 (€190 motor tax). Using 2020’s WLTP (2021 in Ireland) emission testing the CO2 figure rises to 127g/km. To put that in context the equivalent diesel saloon produces130g/km of CO2.
Mazda has a history of using engines that are the right size for its cars. If a conventional 2 litre is needed then it won’t build a 1.5 and add a turbocharger to bring the power back up just for the sake of reducing engine displacement. The Skyactiv-X 2 litre engine’s technology is scalable, so larger or smaller engine capacities may get it in the future. Production of the engine will run in parallel with Mazda’s G and others and will be built per customer demand. It has more costly components than the Skyactiv-G’s 2 litre and Mazda says it will be price accordingly. There are no plans to sell the new X engine to other manufacturers.