THE FIVE MOST FRUGAL CARS
DOING 100km of general running about for less than five bucks in fuel, makes motoring pretty affordable. As manufacturers bring out more models with increasingly-amazing frugality, motorists are laughing all the way from the pumps.
A generation ago, the 30 miles per gallon mark (9.4 litres/100km in metric speak) was a fairly good figure to achieve, with only the little, low-powered super-sippers doing better than 40 miles per gallon (7 litres/100km).
Now, however, the best of the fuel misers are achieving official results of better than 4 litres/100km (70 miles per gallon). Just as importantly, they are cars that perform OK in the cut and thrust of everyday commuting and most will readily hold their own on a run to Victor or the highway to the Barossa.
There’s no need to creep along getting in others’ way, when you’ve got 80kW of power and 250Nm of torque under the right foot – as is the case with two of the top five fuel economy cars on sale in Australia.
Three main considerations drive auto engineers to develop these fuel-sipper engines: 1. The cost of oil in the long term will rise, making filling the car more expensive. 2. The world will run low on oil (we are using it at a greater rate than we are discovering it), and so it has to be stretched further. 3. The environment and people’s concern for it means it’s important when the less fuel burnt per kilometre creates less exhaust emission; and cars might be taxed on their emission rating here one day.
The best advances have been made with diesel-fuelled engines. The fuel is squirted into the engine in carefully measured tiny amounts under enormous pressure thanks to modern ‘‘common rail’’ injection systems.
The injection process is helped by cleverly-designed turbochargers (using the engine’s exhaust gasses to spin a turbine that pushes more air, and therefore oxygen, into the cylinders).
Combined with optimised shape of the combustion chamber, there is great efficiency of power achieved from every drop of fuel, a help to fuel economy and emissions.
Similar work is being done on petrolfuelled engines, but the standout characteristic of diesel engines – torque, or pulling power, at low engine revs – gives them an advantage of fuel economy.
Diesel cars can get into their higher gears sooner and at relatively low speeds. And once settled, the engine ticks over at a low speed and so uses less fuel.
Take the Fiat 500, for example. It’s 1.4-litre engine running on petrol is quite economical. Maximum torque of 131Nm comes at 4250rpm and its official fuel economy is 6.3 litres/100km. But its 1.3-litre JTD diesel brother has more torque, 145Nm, at about a third of the engine speed, 1500rpm, and its fuel economy is 4.2 litres/100km.
The little petrol engine uses 50 per cent more fuel while giving similar on-road performance.
The top petrol-only car on the fuel economy list from
www.greenvehicleguide.gov.au is the tiny smart for two. It has an engine of just one litre size and three cylinders and is only a two-seater. But its light weight means the modest 55kW power is enough.
Hybrid cars – those that have a conventional engine plus and electric motor, exemplified by the Toyota Prius – come into their own in stop-start commuting. Normally, when a driver presses the brake pedal it is the enemy of fuel economy: you’ve burnt fuel to build speed only to waste it by braking and converting to heat energy that is lost. The hybrid car harnesses that energy, like an electricity generator, and feeds it to the battery pack for an electric motor that assists propelling the car.
But hybrids are not so beneficial in open road driving where they run on their conventional engine only and still carry the weight of the electric motor and batteries with little chance to use brake regeneration.
However, the Prius is the third-best in fuel econ of all cars.
Some fuel-wise cars have stop-start: when the is stopped and in neutral, the engine shuts off. It res as the driver presses the clutch pedal to move gear.
Engines done, the auto engineers then enhanc efficiency of their fuel misers by making them in weight (they ditched the spare wheel of the Fiesta ECOnetic to cut weight) and they run on rolling resistance, thin, tyres.
Aerodynamics also get attention. Look at the p style wheel covers on the Volvo C30 DRIVe. The F ECOnetic sits lower than other Fiestas and h deflector skirt under the front wheel while the M D has underbody smooth airflow design. Prius b a drag co-efficient of .25 (anything below commendable; this is very good for a four-doo
Jim Wishart, left, has the Mini Diesel filled up by an attenda Adelaide this week.