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    FAQs

    Octane & Other Gasoline Basics

    Octane
    1. What is octane?
    2. What octane does my vehicle need?
    3. Why does my vehicle require a higher octane gasoline than is recommended in my owner's manual?
    4. Why is ethanol an effective octane booster?
    Other Gasoline Basics
    1. How is gasoline made?
    2. What does reference fuel mean?
    3. What does (R + M) / 2 stand for?
    4. What are hydrocarbons?
    5. What does hydrocracking mean?
    6. What does the hydrotreating process do?
    7. What is the difference between on-road diesel fuel, off-road diesel fuel and low sulphur diesel fuel?
    8. What's the term used for lubricating moving parts?

     

    Octane

    1. What is octane?
      A gasoline's octane number is a measure of its ability to resist knocking as it burns in the combustion chamber of an engine. A spark from the spark plug starts normal combustion. The flame travels across the combustion chamber rapidly and smoothly until all the fuel is consumed. Abnormal combustion occurs when part of the fuel/air mixture ignites spontaneously and burns very rapidly, causing the pressure to rise suddenly. This results in a metallic knocking or pinging sound. A gasoline's ability to resist knocking is called its anti-knock quality. The octane number of a gasoline indicates the anti-knock quality of the fuel. A gasoline's octane number is determined by comparing its resistance to knocking to the performance of reference fuels in a test engine.

    2. What octane does my vehicle need?
      To determine your vehicle's octane requirement, look at the manufacturer's recommendation in your owner's manual. Most auto manufacturers recommend 87 octane gasoline, as measured by the (R + M) / 2 method on a test engine under defined operating conditions. If the vehicle knocks on the recommended grade, a higher octane grade should be selected. Some foreign vehicle manuals recommend a Research Octane Number (RON) instead of the more common octane rating that appears on most gasoline pumps. As a rule, the recommended octane rating can be determined by subtracting four (4) from the recommended RON number. A vehicle that calls for "91 RON" should use 87 octane gasoline (as measured by the (R + M) / 2 method). Using a higher grade than is required will not usually increase performance. However, if the vehicle is equipped with knock sensors, as many late model vehicles are, a higher octane grade may enhance performance.

    3. Why does my vehicle require a higher octane gasoline than is recommended in my owner's manual?
      There are two reasons. First, the engine may be at the upper end of the octane requirement range for the particular model. It may, therefore, knock during periods of heavy engine load. The octane requirement for each engine in vehicles of the same make is different because of variations in manufacturing tolerances. Industry testing has shown that this difference can range between two and five octane numbers. While you will not hear knock, the spark timing will be retarded, resulting in loss of power and performance.

      The second reason for using a higher-octane gasoline than recommended could be to counter the buildup of combustion chamber deposits resulting in a higher than average octane requirement for the engine. Industry testing shows that the octane requirement increase (over the initial 20-50,000 kilometres) can be as much as nine octane numbers. This means that a vehicle that was originally designed for 87 octane fuel may eventually require 91 octane fuel to perform satisfactorily.

      Petro-Canada's premium gasoline, SuperClean, contains a higher level of Tactrol, our exclusive deposit control additive, than our other grades and will help clean up deposits left by lesser gasoline brands.

      Our two super-premium grades, SuperClean 94 (Montreal supply area) and Ultra 94are our highest octane gasolines. They have all the attributes of SuperClean and a higher detergency level that will help clean your car’s fuel injectors and intake valves and help keep them clean. Cleaner engines help provide optimal fuel economy, reduced emissions and maximum performance.

    4. Why is ethanol an effective octane booster?

      The octane number written on the gas pump is Anti-Knock Index (AKI). It’s an average of two octane ratings using the same test equipment but using different operating conditions. The methods produce a Research Octane number (RON) and a Motor Octane Number (MON). Both were once considered important and that’s why AKI is an average of the two. With modern engines and fuels systems, recent studies have shown that RON is more important than MON. So in these cars, the higher the RON the better these cars perform. For an AKI rating of 91 the lower the MON the higher the RON. This difference is called sensitivity. All gasoline components have different sensitivity. Most hydrocarbon components have low sensitivity.  Ethanol has high sensitivity and so, modern performance cars benefit from gasolines with ethanol. Why does ethanol have higher sensitivity? One reason is related to the cooler combustion that results from ethanol combustion. Higher knock tendency is directly related to higher combustion temperature.

      Here is a comparison of two fuels with different octane with and without ethanol.

      91 Grade - no ethanol
      RON 97.2
      MON 85.6
      Ultra 94 - with ethanol
      RON 101.5
      MON 88

      Notice the difference in RON number from 91 grade without ethanol (97.2) and the RON of Ultra 94 (101.5). The difference is 4.3 numbers. That is significantly more than the 3 numbers difference between 94 and 91 AKI labelled on the pump. That is why gasoline with ethanol can be the best performance fuel for today's cars.


          Other Gasoline Basics
        1. How is gasoline made?
          Gasoline is manufactured from crude oil through a series of physical and chemical processes in an oil refinery. The end product, a blend of several refinery streams containing hundreds of chemical compounds called hydrocarbons, must meet over 20 different requirements to be considered a suitable gasoline for use by a wide range of vehicles.
          Rigorous quality control tests are conducted prior to releasing the gasoline into the market place. In some cases, additives are included to improve specific properties of the gasoline.

        2. What does reference fuel mean?
          In the measurement of octane quality of gasoline a mixture of two hydrocarbons called iso-octane and normal heptane. Iso-octane is assigned an octane rating of 100, and normal heptane is assigned an octane rating of zero. A blend of 90% iso-octane and 10% n-heptane would have an octane rating of 90 octane.

        3. What does (R + M) / 2 stand for?
          This is the Road Index — the average of Research Octane Number and Motor Octane Number; one measure of the combustion quality of gasoline.

        4. What are hydrocarbons?
          Hydrocarbons are compounds composed of carbon and hydrogen.

        5. What does hydrocracking mean?
          Hydrocracking is a severe, high temperature, high pressure refinery process that converts heavy black oil into gasoline and diesel fuel by cracking or breaking up larger molecules in the presence of hydrogen and a catalyst.

        6. What does the hydrotreating process do?
          The hydrotreating process reacts a fraction of crude oil with hydrogen at high temperature and pressure, in the presence of a catalyst, to improve colour and odour, and reduce sulphur content.

        7. What is the difference between on-road diesel fuel, off-road diesel fuel and low sulphur diesel fuel?

          On-road diesel fuel This refers to diesel fuel that is used for on-road purposes, or for off-road vehicles designed for on the road. This fuel has a maximum sulphur level of 15 parts per million (ppm).

          Off-road diesel fuel — This refers to diesel fuel that is used for off-road purposes (i.e., mining, farming, etc.). This fuel is frequently dyed red or "marked" to show that it is exempt from provincial road taxes. This fuel has a maximum sulphur level of 15 ppm.

          Low sulphur diesel fuel — This fuel contains less than 500 ppm (0.05 weight per cent) sulphur, and can only be manufactured until 2012. It may be sold to railways and for marine use.

        8. What's the term used for lubricating moving parts?
          It's called lubricity and it describes the property of diesel fuel that lubricates moving parts in fuel pumps and fuel injectors to minimize wear.