David Motton
Tow Car Editor

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The future's not just about electric: Mazda has a new engine that combines the best of petrol and diesel power.

The internal combustion engine is on borrowed time. Come 2040, sales of new petrol and diesels will be banned, and the rapid development of electric alternatives means the clock could wind down even sooner.

So many think, at least. Mazda has other ideas. It's not against the electric car - it has just unveiled its first electric model, the MX-30. But it believes the internal combustion engine shouldn't be written off too soon.

The best of petrol and diesel

To prove its point, Mazda has developed a new engine that promises to combine the best of petrol and diesel power. Called the Skyactiv-X, it burns petrol but uses compression ignition like a diesel.

Or more precisely, it uses what Mazda describes as Spark Controlled Compression Ignition (SPCCI). If you don't mind a brief technical explanation, the engine injects a lean air-fuel mixture, compressing it up to 16:1, which is just below the level required to achieve compression ignition. To ignite the mixture at the right time, a small injection of atomised fuel directly around the spark plug builds a richer core. When fired, this small core creates a pressure wave that runs through the combustion chamber, increasing the compression and temperature to the critical point where the main body of fuel combusts.

Got that? Good. The upshot of all this clever tech is that the engine produces tiny levels of NOx, pollutants that are harmful to local air quality, while emitting low levels of carbon dioxide - just 96g/km in the Mazda 3.

Mazda also claims the engine delivers the free-revving performance of a petrol with the mid-range response of a diesel. That should, you would hope, make it well suited to towing a caravan.

To start with, the Skyactiv-X engine is available in the Mazda 3 small family car. Early next year it will be available in the new CX30 SUV.

We've had a chance to try the engine in the new 3. There was some diesel-like clatter and grumble from the engine at low revs, but the engine was quiet once cruising. And while accelerating, it sounded more like a petrol than a diesel.

Does it really offer the best of both worlds?

Well, peak torque doesn't arrive until 3000rpm, whereas a diesel typically generates maximum pulling power at around 2000rpm. So the engine needs to be worked a bit harder before it really starts to shift. Maximum torque is 165lb ft, where a typical 2.0-litre diesel might produce closer to 240lb ft.

Compare the Skyactiv-X to other petrol engines, and it's by no means the strongest in terms of mid-range pull. For example, the Volkswagen Group's 150hp 1.5-litre TSI petrol produces 184lb ft, although it doesn't match the Mazda's 180hp top end. VW's 2.0-litre TSI has 190hp and 236lb ft.

So, if one of the benefits of the Skyactiv-X engine over a conventional petrol is supposed to be a diesel-like mid-range, there are already other petrol engines that do a better job. However, in fairness to Mazda these engines don't come close to the SkyActiv's exceptionally low emissions.

Mazda's M Hybrid technology also contributes to the car's economy, using a 24V mild-hybrid system to recover energy when slowing down and using it to assist the engine.

Matching tow car with caravan

The Skyactiv-X engine is available in the saloon and hatchback, with a choice of manual or automatic gearboxes. The hatchback's kerbweight is 1542kg with the manual 'box, rising to 1574kg with the auto. That gives an 85% matching figure of at least 1311kg. However, the towing limits is 1300kg, so a caravan weighting 85% of the Mazda's kerbweight doesn't make a legal match.

Judging by our solo drive, the engine should be strong enough to cope with a 1300kg caravan, although it will need to be worked harder than a diesel (and some petrols).

The only way to reliably judge a car's towing stability is to tow with it, but the 3's firm and controlled ride suggests the Mazda should make a secure tow car. It's certainly one of the most entertaining small family cars, with alert handling and precise and well weighted steering.

What's it like inside?

Build quality is good, with a sporty looking interior design. There's enough leg and headroom up front but rear-seat space could be more generous. A Škoda Scala has a lot more rear legroom.

The boot is a reasonable size whether you opt for the hatchback (351 litres) or the saloon (444 litres) although there is a big load lip to lift items over.

Prices for the 3 start from £20,595. That's for the 122hp petrol, without the clever tech of the Skyactiv-X. If you want the more advanced and powerful engine, prices begin from £23,555. Those are reasonable prices when you consider how well equipped the 3 is. All models have Bluetooth connectivity, a digital radio, and Apple CarPlay and Android Auto. Sat-nav and air conditioning are also standard across the board.

To look at and to drive, the 3 is very appealing. But some rivals are more roomy, and most have a much wider choice of engines. For tow car drivers, we can't help thinking a diesel would be a better bet than petrol, even when that petrol engine is as advanced as the Skyactiv-X.