The key difference between unleaded and super unleaded petrol is that Unleaded petrol has minimum RON 91 whereas super unleaded petrol has minimum RON 97-98.
The term RON stands for Research Octane Number. It is a measure of the effect of fuel on an engine. We can measure it by running the fuel in a test engine under controlled conditions (with a variable compression ratio) and comparing the results of this test with a mixture of isooctane and n-heptane.
CONTENTS
1. Overview and Key Difference
2. Why is Lead Added to Petrol
3. What is Unleaded
4. What is Super Unleaded
5. Side by Side Comparison – Unleaded and Super Unleaded in Tabular Form
6. Summary
Why is Lead Added to Petrol?
Petrol is a volatile liquid form of hydrocarbon fuel. We can isolate it by fractional distillation of petroleum, and it is useful as a fuel in the internal combustion engines. Manufacturers mix some additional compounds with petrol in order to enhance its use in engines. Hydrocarbons like isooctane or benzene and toluene are some examples of such additives which are important in increasing its octane rating. This octane number measures the ability of an engine to cause self-ignition in the engine cylinders (which causes knocking).
Figure 01: Leaded Petrol is not in use at present due to its harmful effects
In premature ignition, when petrol and air mixture caught before the spark passes through the spark plug, it pushes against the crankshaft producing a knocking sound. Because of this knocking, the engine tends to overheat and loose power. Therefore, it damages the engine in the long run. Therefore, we should increase the octane number of the fuel. Other than adding hydrocarbons stated above, we can increase the octane number by adding certain lead compounds as well.
What is Unleaded Petrol?
This is a type of petrol that does not contain lead. As stated above, lead compounds are useful as anti-knock agents for fuel. But, it is a highly toxic element to humans and other animals. Moreover, when these compounds burn in the engine lead particles will come out with the fumes. They will be accumulated in the respiratory tracks of organisms causing health problems. In the extreme conditions, this element can be even carcinogenic. Furthermore, it causes environmental pollution. Because of these reasons, lead-containing petrol is now not in use, and instead, people use unleaded petrol. This form of petrol does not produce harmful fumes containing lead.
People discovered various strategies to eliminate the knocking problem in vehicles by using unleaded petrol. One solution is by adding aromatic hydrocarbons to increase the octane rating. However, this octane rating is little lower than that is expected from leaded petrol. Another way is to produce engines, which do not cause pre-ignition. Furthermore, car-manufacturing companies produce engines with better fuel burning techniques. Cars with catalytic converters are an example, and these cars use unleaded petrol.
What is Super Unleaded Petrol?
Super unleaded petrol has a minimum research octane number (RON) of 97-98. Therefore, the octane number is very high in this type of petrol even than the premium unleaded petrol. Although the pricing is very high, this petrol grade is remarkably efficient and productive.
In order to avoid problems, cars which have designs that are suitable to run in higher octane rating fuels, like super unleaded petrol, should not be filled with lower octane rating fuels.
What is the Difference Between Unleaded and Super Unleaded?
Unleaded vs Super Unleaded |
|
| A form of petrol that has no added lead compounds. | Has no lead compounds and has a high octane rating than unleaded petrol. |
| RON Value | |
| Unleaded petrol has minimum RON 91. | The minimum RON is 97-98 for super unleaded petrol. |
| Price | |
| Less expensive compared to super unleaded petrol. | Highly expensive compared to unleaded petrol. |
| Performance | |
| The overall performance of leaded petrol is lower than that of super unleaded petrol. | The overall performance of super unleaded petrol is much higher than that of unleaded petrol. |
Summary – Unleaded vs Super Unleaded
Lead compounds are added to petrol in order to decrease the knocking effect on engines. However, due to the toxic effects of these compounds, now they are not in use. Therefore, manufacturers have discovered different forms of petrol that have no lead compounds. The difference between unleaded and super unleaded petrol is that Unleaded petrol has minimum RON 91 whereas super unleaded petrol has minimum RON 97-98.
Reference:
1. “Unleaded Petrol and Pre-1986 Cars – Facts About Fuels.” RACQ. Available here
2. “Gasoline.” Wikipedia, Wikimedia Foundation, 14 May 2018. Available here
Image Courtesy:
1.’7822806770′ by Michael Coghlan (CC BY-SA 2.0) via Flickr