Why LPG is Australia's Only Truly Viable Alternative Fuel

The gas that's far cheaper than, and almost as good as, petrol

When Quentin Tarantino shouts ‘Action!’ and three hot chicks in yellow latex jumpsuits hammer their flamethrowers, you’re about to see propane do what it does best – burn. Propane is the pyrotechnic gas du jour for the Hollywood special effects set. It’s the same stuff that makes gas barbecues happen right across Australia, and if a licensed installer jams a big enough tank of it in your car (plus sundry plumbing), it’s a fair old substitute for petrol. (LPG actually has butane and other stuff in it as well, but it's mostly propane.)

POPULARITY

Propane wears the nom de plumes ‘Autogas’, LPG and Liquefied Petroleum Gas. It is in fact Australia’s most popular alternative fuel. Widespread delivery infrastructure is already in place – and that’s just not the case with most other popularised alternative fuels (read: hydrogen and EVs). Of Australia’s 4500 servos, 3200 stock LPG. According to the Australian LPG Association, there are 109 LPG outlets between, for example, Sydney and Brisbane, and the furthest distance between LPG refuelling points is 72km.

Australians are slowly embracing LPG. Since 2005, the number of motorists driving on LPG has tripled. Last year, 125,000 LPG conversions were performed – approximately one for every 100 cars. The 2008 spiralling price of petrol helped, as did the then-Howard Government’s LPG rebate – when introduced in August 2008 it paid $2000 to private buyers doing aftermarket conversions, and $1000 for those buying a new, factory-fitted LPG vehicle. Installers were instantly swamped by increased demand.

The conversion rebate dropped to $1750 on July 1, 2009, and will reduce by $250 every 12 months until it reaches $1000 (slated for July 1, 2012, unless the pollies change their minds). It’ll be phased out on June 30, 2014. The $2000 new-vehicle LPG grant remains. Conversions typically cost $2500-$4500, so payback periods are generally extremely short – depending on how many kilometres you drive. (And you simply can’t say that about, for example, a Toyota Prius.)

ENERGY DENSITY

Kilojoule for kilojoule, you need 1.35 litres of LPG to deliver the same energy as 1.0 litre of petrol, which explains why fuel consumption increases by about one third if you switch to LPG. (As a ready-reckoner: 880ml of diesel, 1.5 litres of ethanol and 1.52 litres of LNG – liquefied natural gas – are also equivalent to one litre of petrol.) Increased thirst for LPG is more than offset by lower pump prices, currently about half the price of 91-octane unleaded. There is also a claimed 10 per cent reduction in CO2, as well as a cut in some toxic exhaust gas emissions.

ENERGY SECURITY

These are not the only sound reasons for converting to LPG. Dr Laurie Sparke, Holden’s former Advanced Engineering boss, says LPG could be one key to securing Australia’s energy security into the future. Dr Sparke has gone on the record in several forums, claiming within 5-10 years Australia might not be able to buy oil – at any price – if rising global demand for oil continues. “Australia is going to lose access to oil first in the western world,” he said. “This is a national issue. It has to be faced by everyone – industry and government – otherwise we are going to end up in serious strife.”

The basic problem: oil basically cannot be produced faster than right now. Supply is fixed. Demand – especially from the burgeoning economies of China and India – is accelerating rapidly. Currently China has 25 cars for every 1000 of its population. When – not ‘if’ – it achieves per capita car ownership similar to ours (700 cars per 1000 people) it will double the number of cars on earth (to 1.8 billion; currently 900 million).

That’s a big potential problem for Australia, dependent as we are on foreign oil.

Ramping up the LPG industry to convert millions – instead of the current 112,000 – of cars to avoid running dry on petrol will be an ambitious undertaking. It’s doubtful Governments are even aware of the upcoming fuel crunch, despite Dr Sparke’s words and the CSIRO’s Fuel for Thought report, which echoed his sentiment in 2008. Hopefully, someone in a position to act will whip their heads out of the sand in time.

INSIDE THE GAS TANK

The background briefing on LPG and its closest competitors: LPG is three carbon atoms wrapped in eight hydrogens (petrol: eight carbons plus 18 hydrogens). It’s about 1.5 times heavier than air. It’s produced both by natural gas processing and by petroleum refining, so it’s a lucky thing Australia has significant natural gas reserves. (Natural gas is the simplest hydrocarbon gas – methane – which is one carbon atom and four hydrogens.)

Luckily, propane doesn’t mind being liquefied – all you have to do is squeeze it. If you compress it about 12 times more than the air you’re breathing now, it condenses into a liquid. So the pressure’s not that high inside those LPG tanks, as gasses go. (Compressed natural gas is about 250 times more compressed than the atmospheric air we’re ingesting.)

Unfortunately, it’s much harder to liquefy natural gas. It doesn’t matter how hard you squeeze it, it just won’t liquefy at normal temperatures. If it’s hotter than minus-83 degrees C outside, forget it. Liquefied natural gas (LNG) needs to be chilled. Special cryonic vessels to keep LNG down around -160 degrees C, which isn’t really all that practical for the boot of your car. Compressed natural gas (CNG) isn’t perfect either. Even compressed to 250 atmospheres you still need almost four litres to provide the same energy as one litre of petrol. That’s one very big tank of very high-pressure gas.

LPG has an Octane rating of 110 – higher than petrol. Theoretically it could handle far more compression than in a petrol engine, but dedicated LPG engines are unavailable.

There’s a slight power deficit on LPG is because it enters the engine as a gas. Petrol enters as a liquid, which evaporates and chills down, increasing the density of the fuel-air charge. That’s why LPG companies are working on liquid-injection systems now as the next logical step for LPG development.

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