RON. This acronym is seen everywhere, from local service stations to car articles and reviews.
It stands for Research Octane Number, a measure of the octane rating of gasoline. In Australia, the octane rating goes above 98 for premium unleaded, before retreating to 95 premium unleaded, E10 (94 octane) and standard 91 octane unleaded. United fuel also offers an E85 racing blend rated at 107 RON.
What is the octane rating? As discussed earlier, it describes the fuel’s ability to resist premature detonation – which causes engine knock. The term comes from the knocking sound an engine makes if its fuel explodes too early, before the spark plug is ignited to ignite it.
Knock is also related to the compression ratio of the engine. A standard internal combustion engine has several cylinders, each with a piston.
The compression ratio describes the cylinder volume when the piston is at the bottom of its stroke (bottom dead center, or BDC) versus the top of its stroke (top dead center, or TDC). If the volume at BDC is 10 times that at TDC, then the engine’s compression ratio is 10:1.
Engines with higher compression ratios tend to have greater thermal efficiency, which in the simplest terms means they make more power and provide better fuel economy compared to their lower compression counterparts, assuming all else is equal.
Fuels with higher RON burn at hotter temperatures and under greater pressure. This makes it ideal for these high compression ratio engines because, by not burning before the piston reaches TDC, the risk of knocking is reduced.
In Australia, this is the main reason 98 RON unleaded is branded as premium. Not only is it the most expensive gasoline a consumer can buy from bowser, it has the greatest knock resistance.
95 premium unleaded, E10 and standard 91 unleaded have lower knock resistance. In high compression ratio engines, they can produce less power and reduce fuel economy.
Does my car need premium unleaded high RON?
A general rule of thumb is that older cars will happily accept anything from standard 91 unleaded all the way up to premium 98 octane gasoline. Newer cars with high compression ratio engines, especially those with turbocharged engines found in most European brands, really like 95 or 98 premium unleaded octane.
It is important to note that today’s cars have electronic fuel injection (EFI) systems. This contains a sensor that can detect if an engine knock occurs.
If this happens, the system can adjust the spark ignition timing to prevent it from happening again. However, this can come at the cost of power and fuel economy.
What does all this mean? In emergency situations where premium unleaded may not be available, in some cases, you can fill the car with standard gasoline. The safest bet remains to follow the manufacturer’s guidelines and recommendations to ensure the longevity of the car, and to ensure that its performance and fuel economy are maximized.
However, note the cars in Australia that are equipped with gasoline particulate filter (PPF). These are filters that reduce harmful emissions and air pollution by trapping pollutants such as soot.
Vehicles equipped with PPF may only run on higher octane fuel, risking serious damage to the engine and exhaust system.
Does premium fuel clean car engines – and is this necessary?
In short, premium fuel may have the ability to clean the engine, but it is certainly not a necessity.
Fuel companies such as Shell, Caltex and others often describe this cleaning ability as a unique advantage of 98 premium unleaded, but today’s vehicles are already equipped with fuel filters to prevent any impurities that can damage components such as the fuel injection system.
A better idea to keep the engine clean and free of any possible carbon build-up is to adhere to the manufacturer’s recommended service intervals, and take longer road trips every now and then that ensure the car’s engine reaches ideal operating temperature for a sustained period of time.