Petrol Types Explained

Petrol Types Explained

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Unless you drive an EV, diesel or LPG vehicle, you’ll be met with different petrol types each time you fill up.

E10, E85, 91 RON, 95 RON, 98 RON - we investigate.

Firstly, the price fluctuations

In most major cities and population centres in Australia, petrol prices fluctuate. The difference can be as much as 50 cents per litre or more from peak to trough.

In Sydney and Melbourne, a petrol cycle, the peak-to-peak time, is typically around 3 to 4 weeks. In Adelaide, around two weeks and Perth, around a week.

Check the ACCC’s petrol price cycles for more specifics.

Why?

Although external factors like the value of the Australian dollar and supply and demand have an effect on petrol prices, the reason for the petrol price cycles is the result of deliberate pricing policies of petrol retailers.

As stated on the ACCC website ‘Price cycles are the result of deliberate pricing policies of petrol retailers, and are not directly related to changes in wholesale costs’.

Competition between retailers also plays a part in the cycles as well as location. In larger cities where there are more petrol retailers, you’ll typically see lower prices than in rural areas.

Australia imports petrol from Singapore and South Korea among other countries so international prices also play a role.

In a nutshell, petrol stations compete for a share of the market in their area but are influenced by many other factors.

Also, the Australian Government fuel excise (tax) adds 41.2 cents per litre to the cost of fuel.

‘E’ and ‘RON’

Ethanol

E10 fuel is regular unleaded petrol mixed with 9-10% ethanol. Ethanol is an alcohol that can be used as a renewable alternative fuel. Commonly, it comes from starch left over from wheat or sugar production and can be locally sourced in Australia.

Ethanol blended fuel can reduce emissions and lower the price of petrol.

They should just make E100 then.

In some countries, they do. However, not all engines are able to run efficiently on ethanol-based fuels. Some experience stalling if the water in the ethanol separates from the petrol. There are also corrosion and clogging risks in some engines.

When governments and fuel retailers offer a product, they don’t want lawsuits and complaints from motorists with repair bills.

Most modern cars using regular unleaded petrol are compatible with E10, but make sure to check with the manufacturer.

E85 is on another level.

This is between 70% and 85% ethanol and unleaded petrol and only available from select retailers. E85 is sometimes referred to as ‘flex fuel’ due to varying levels of ethanol.

E85 is suitable for tuned, flex-fuel vehicles and is popular in motorsport. In fact, the V8 Supercars use a blend of E85. E85 gives better performance, torque and thermal efficiency (less energy lost to heat).

E85 has the ability to decrease engine temperatures because a lot of water vapour is formed when alcohol is burned. The water vapour helps to draw heat away and cool internal engine parts.

RON (Research Octane Number)

When referred to as ‘detonation’, it can’t be good for an engine. It isn’t.

In Australia, we commonly see 91, 95 and 98 RON unleaded petrol. As most motorists know, the higher the RON, the higher the price.

Octane is a molecule with eight carbon atoms. Car engines love these molecules. The more octane molecules there are in fuel, the slower, cooler, and more controlled the burn is.

  • 91 RON (regular unleaded) is 91% octane.
  • 95 RON is 95% octane.
  • 98 RON is 98% octane.

Higher quality fuels reduce engine knock

Engine knock, also known as detonation or ‘pinging’ is when some of the air / fuel mixture burns without being ignited by the spark plug.

When referred to as ‘detonation’, it can’t be good for an engine. It isn’t.

When knock occurs, part of the air / fuel mixture combusts before the spark plug fires. Then, milli seconds later, the spark plug ignites the remaining pocket of air / fuel mixture.

As different pockets of fuel burn inside the engine’s cylinder at different speeds and times, they collide causing two ‘flame fronts’. This results in a large spike of pressure and heat.

Using fuel with a high octane rating dramatically reduces the change of knock.

Which fuel is right for me?

It goes without saying that the right fuel is the one the engine was designed to run on. Some motorists find that higher octane fuels offer better fuel economy so the extra cost is worth it.

Others say that flushing a full tank of high-octane fuel through the engine once in a while also has benefits.

Check your owner’s manual or a qualified mechanic to make sure your car is on the best diet available.

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