Internal Combustion Engine

An internal combustion engine (ICE) burns fuel in the combustion chamber formed by the piston and the cylinder. Fuel energy is converted to work to drive the piston down. Below are two types of internal combustion engines:

  1. Gasoline spark ignition (SI) engines require a spark from an electric spark plug to start the combustion process during the compression stroke.
  2. Diesel compression ignition (CI) engines do not require a spark. The diesel fuel auto-ignites when it sprayed into the cylinder during the compression stroke.

The Combustion Chamber

A combustion chamber is that part of the internal combustion engine in which the fuel/air mix is burned. It is where air is sucked in and combined with fuel, compressed, burnt and then released to exhaust – this is known as the four-stroke Otto cycle.

In gasoline engines, the spark plug initiates combustion giving a smooth burn that develops pressure, forcing the piston down. However, under high pressure and temperature some gasoline fuels can show a tendency to combust spontaneously. This can result in a ‘knocking’ or ‘pinking’ sound as small erratic bursts of combustion occur. Thus, an engine may suffer from depleted performance and in the most severe cases permanent damage can occur. Gasoline fuel’s octane number is a measure of how well the fuel can resist this knocking.

Timing of combustion is critical to the effective energy transfer from the burning fuel to the engine. Depending on engine design (e.g. octane responsive engines), use of a higher octane quality (than originally recommended by the vehicle manufacturer) can allow advanced ignition timing (i.e. earlier spark) that can result to improvement in engine performance.

Fuel Injectors

For gasoline spark ignition engines, there are two types of technologies on how the fuel is delivered to the combustion chamber:

  1. Port fuel injection (PFI) engines – fuel is injected onto the back of the hot inlet valves and evaporates to mix with the fresh air before entering the cylinder during the intake stroke.
  2. Gasoline direct injection (GDI) engine – fuel is injected directly into the cylinder.

It is the job of the fuel injector to ensure that the fuel is dispersed and mixed into the air in the exact pattern and volume required. Some fuels can lead to fouling of the injector holes, which can disrupt the spray pattern, affecting the efficiency of the engine.

Inlet Valves

Inlet valves perform the job of opening and closing several hundred times a minute, depending on engine design, to allow the air, or the air/fuel mix, into the combustion chamber. In a conventional port fuel injected gasoline engine, inlet valves can be prone to deposit formation, which can potentially affect efficiency of engine and may result to poor responsiveness.

Piston and Piston Rings

Pistons transfer the force from combustion to the connecting rods while piston rings are designed to form a seal between the piston and the cylinder wall. Pistons slide up and down the cylinder bores several thousand times a minute.

Our Commitment To Quality Fuel

Shell has played a leading role in developing high quality fuels. For over 100 years, Shell scientists have been using their passion and expertise to create some of the world’s most advanced fuels for the changing needs of our customers and their cars.

We welcome the Pakistani Government’s decision to upgrade Pakistan’s fuels portfolio. Not only does this benefit our consumers with the use of higher octane number (or Research Octane Number, RON) gasoline fuel, at par with other countries in our region, but also allows Shell to bring in our premium fuels giving our customers more choices and higher quality fuels.

What is Octane number or RON?

The octane number or Research Octane Number (RON) is a measure of how well the fuel can resist this knocking and is often considered to be a quality index that enables the customer to distinguish between premium and regular grades.

Higher octane fuels (e.g. premium gasoline grades) are more resistant to auto-ignition (knock) in a gasoline engine. Through the engine management system, modern engines are able to detect combustion quality (knock) and engines often adjust their settings (ignition timing) to exploit higher octane fuels. This adaptation of the ignition timing allows higher octane fuel quality to be exploited, which can result in improved performance of the engine.

Gasoline fuels with higher octane number are usually sold at a higher pump price. Refer to your car’s manual or manufacturer for the minimum octane number recommended for your vehicle.

Formulated Gasoline Fuels

Shell has more than a century of experience in fuels development. We have 170 fuels scientists and specialists across the globe working on fuels innovation, development and product implementation to meet the evolving needs of customers and their cars. They’re passionate about finding smarter ways to create better, more efficient fuels. It is this experience that makes us a leading provider of new and innovative fuels today.

Shell Super Unleaded is designed to help to prevent the build-up of deposits that can harm your engine’s performance over time. Shell Super contains our unique fuel economy formula at no extra cost to our customers.

Premium Fuels

The difference between premium and regular gasoline fuels can be the octane number of the fuel and the technology of formulation used.


  1. How is the Pakistani fuels landscape changing?
    The Pakistani Government’s has decided to upgrade Pakistan’s fuels portfolio. All imports will now be of RON 92, with most refineries also producing higher quality petrol. This will mean as a customer the new standard petrol will be of a higher rating than the previous RON 87 throughout the country (actual RON ratings will vary depending on the product sourcing and the region where you purchase). You will also notice the color of standard petrol will change from ‘pink’ to a light green color.
    The Government has also deregulated RON 95 & RON 97 grades, allowing OMCs to import market and sell these products as they see fit. The benefits for the Pakistani consumer are tremendous as they bring our country at par with global standards of quality and environment and allow companies like Shell to bring its global portfolio offering to Pakistan.
  2. What is octane?
    The octane ratings relate to the fuel's ability to resist pre-ignition or "knocking", which is an uncontrolled explosion of fuel in the combustion chamber.
  3. What are the RON/Octane levels of Shell’s fuels?
    Shell’s Main Grade:

    As per Government regulations Shell Pakistan will offer product sourced from local refinery with RON level higher than 87 RON.
    Shell’s Premium Grade:
    The ability to import higher grade product i.e. RON 95 & 97, allows Oil Marketing Companies to choose a strategy they wish to pursue in their offer for higher quality fuels. For Shell, this is a great opportunity to bring in world-class products that deliver an enhanced product experience for our loyal customers.
  4. Why is Shell selling higher RON fuels?
    High octane enables high compression ratios (CR) that OEMs can design their cars with. Higher CR enable better efficiency (better Fuel Economy).
    Consumers benefit through increase in safety and quality of services, availability of clean fuels, and sharing of benefits through cost efficiencies.
  5. Is it better if I use a higher octane in my car? Will I get performance benefits when I use higher RON in my car?
    The higher the octane number of the fuel, the lower is the tendency for uncontrolled self-ignition of fuel. If octane number is too low engine knocking can cause serious engine damage, particularly at high speed and longer periods (for vehicles w/o knock sensors).
  6. How do I know what the octane requirement of my car is?
    Refer to your car manual or manufacturer for the recommended fuel RON rating for your vehicle.
  7. Are all fuels the same?
    All high octane fuels are not the same. Shell offers differentiated high octane fuel, formulated with an engine cleaning detergent. This formula has been developed to provide higher engine efficiencies and better performance.

More in Motorist

Shell station locator

Fuelling journeys, driving connections - Take a trip across the country and our strategically located 780+ Shell forecourts will be a part of your journey, fuelling your visits to family and friends.

Inside Our Stations

We put the service back into service-station, ensuring you always leave us a little happier than when you arrived.