Fu­els par­adise

THE FIVE MOST FRU­GAL CARS

The Advertiser - Motoring - - FRONT PAGE -

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

SAV­INGS:

Jim Wishart, left, has the Mini Diesel filled up by an at­tenda Ade­laide this week.

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