And the winner is...

With petrol prices tipped to nudge $2 a litre, efficient engines are more important than ever. In an ongoing series, Bill McKinnon looks at current and emerging automotive technologies that will help ease consumption and emissions

Hybrids, electric cars and fuel cells will all play a more prominent role in our driving future, but the petrol-powered internal combustion engine isn’t done with yet.

While many people are going down the diesel road, if you’re thinking of buying a new small- or mid-sized car it’s worth doing some research and a few sums before you join them. Why? There is a price disparity of up to 30 cents per litre, diesel cars usually carry a purchase premium of several thousand dollars over petrol equivalents, and fuel consumption figures around town can be comparable.

A Holden Astra diesel automatic hatchback, for example, averages 7.0L/100km according to Australian standard tests. The petrol automatic averages 7.8L/100km.

However the diesel Astra, at $28,990, costs $1000 more than its comparable petrol counterpart, plus you have the 10 to 30 cents per litre diesel fuel price premium to consider. Averaging 15,000km per year, with diesel priced at $1.80 per litre and petrol at $1.60, you’d actually save more – $18 per year – by filling up with petrol. And that’s on top of the $1000 you saved at retail.

So while diesel usually delivers better outright consumption (and is certainly the smarter choice for large, heavy 4WDs), when it comes to smaller/mid-sized cars, petrol power can still cost less.

Compared to Europe, our petrol is cheap. You think $2 per litre will be painful? Western Europeans on average now pay $3 per litre to fill up.

Petrol, by volume, is one of the most potent and efficient forms of energy storage on the planet. Most alternative fuels don’t even come close – that’s the main problem engineers face making them viable for automotive applications. 

The computerised synchronisation and control of petrol engine drivetrains, along with the use of lightweight, low-friction materials, has allowed more precise and efficient use of this energy even in relatively conventional engines.

The 1.8-litre units in the Toyota Corolla and Honda Civic, and the Mercedes A/B200 2.0-litre, score a top 10 finish in the Green Vehicle Guide – partly because, unlike diesels, they produce far fewer toxic gas emissions and no particulates.

Emerging petrol engine technology, which we’ll soon see on a larger scale, includes multi-stage direct fuel injection at extremely high pressures, complemented by ignition timing that’s adjusted several times during each cylinder cycle. This means the minimum amount of fuel is used, and emissions are further reduced, but the engine delivers more performance.

The VW Group (including Audi and Skoda), BMW, Peugeot and Fiat are early adopters of direct petrol injection.

They are also employing turbo-charging and/or super-charging to small- displacement engines – of 1.4 to 1.6 litres – to get the performance of a naturally aspirated 1.8-2.0 litre but with much lower fuel consumption and CO2 emissions.

Variable valve timing and other such systems, which effectively alter engine displacement and/or compression ratio depending upon load, work based on how you drive. If you need lots of power, you’ll get it, but if you don’t, the engine will shut down some cylinders or it will change its running configuration to use minimum fuel.

This technology is becoming more mainstream in the US where it’s employed mostly in larger engines to maintain high power outputs but get fuel consumption down from absolutely terrible to, well, let’s say okay.

In our market, Honda’s new Accord V6 can run on three, four or all six cylinders. Holden will soon introduce cylinder deactivation on the Commodore V8 and Mercedes is interested as well.

Then there is transmission.

While a manual usually puts the engine’s performance to the road more efficiently than an automatic, the reverse is now true in some cars, where autos with five, six, seven or unlimited variable ratios are returning lower consumption figures than their manual counterparts – so it pays to check the fuel averages for both transmissions.

That said, autos can waste fuel through the torque converter, so makers like Fiat, VW and BMW are using a new style of automated manual with a clutch (but no clutch pedal) as another piece of fuel saving/emissions technology.

BMW has coined the term ‘Efficient Dynamics’ as the theme for its fuel-saving engineering. And it’s able to find savings in many places other than the engine and transmission.

It’s using new water and oil pumps, for example, which draw less energy from the engine. Fuel savings are a claimed two per cent per pump. Lower rolling resistance tyres yield a 0.7 per cent saving. Air flaps behind the grille stay closed while the engine doesn’t need any cooling air, lowering wind resistance by seven per cent and producing a one per cent fuel economy improvement.

An automatic start/stop function, which switches the engine off when you’re stationary then starts it again as soon as you press the accelerator, saves three per cent. So does electric power steering and brake energy regeneration, which sees the car’s generator producing power only when the driver releases the accelerator. 

Unfortunately, BMW’s Efficient Dynamics petrol engines – including a new 2.0-litre that produces 125kW of power yet averages just 6.4L/100km – are not yet available in Australia because of the high sulphur levels in our petrol.

“BMW’s new Efficient Dynamics engines are designed to run on clean petrol with a sulphur content of 10 parts per million. Australian petrol’s sulphur content is 50 parts per million. If the Federal Government is serious about reducing emissions it needs to introduce tougher fuel quality standards,” says Toni Andreevski from BMW Australia.

The oil companies claim that bringing in 10ppm petrol will cost them at least $1 billion. Correction: it will cost us at least $1 billion.

So while car makers deserve criticism for a range of sins, it’s also fair to say that, in the Australian context, some are well ahead of legislators and the overall debate about how to reduce fuel consumption. They already have efficient, clean petrol-engine cars at affordable prices.

It’s in their interests to do so, of course, because technology is their business – and if they fall off the pace, they might as well make biscuits instead.

Open Road July/August 2008