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Frequently Asked Questions

  1. What is ULG-91 (E-plus)?
  2. Will ULG-91 (E-plus) be available in all petrol stations across UAE?
  3. What will be the price of ULG-91 (E-plus)?
  4. What are octane ratings?
  5. What is  octane" sensitivity"?
  6. What is "knocking"?
  7. Is knocking harmful?
  8. Why do we need Octane Ratings?
  9. What's the right octane level for your car?
  10. What other factors affect octane requirement?
  11. Will I get better performance from my car if I use a higher octane fuel like ULG-95?
  12. Will higher octane fuel give me better fuel economy?
  13. Will higher octane gasoline clean my engine better?
  14. Should you ever switch to a higher octane gasoline?
  15. What does a low Octane value mean, to me?
  16. What does a high Octane value mean, to me?
  17. Can higher octane fuels give me more power?
  18. Does low octane fuel increase engine wear?
  19. Can I mix different octane fuel grades?
  20. What happens if I use the wrong octane fuel?
  21. How can I be sure that the 91 grade (E-plus) works in my car?
  22. Do I have to tune my car before using 91 octane (E-plus)?
  23. Can I tune the engine to use another octane fuel?
  24. How can I be sure that the station attendant will my car with the required fuel?
  25. What is the effect of engine speed?
  26. What is the effect of engine deposits?
  27. What is the effect of air temperature?
  28. What is the effect of humidity?
  29. Where can I get more information about ULG-91 (E-plus)

General Questions

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1. What is ULG-91 (E-plus)?


ULG-91 (E-plus) is a new less expensive grade of 91 octane petrol that will be available at Adnoc Distribution's filling stations in UAE to customers from the 8th  of October 2006.

2. Will ULG-91 (E-plus) be available in all service stations across UAE?

ULG-91(E-plus) will be available at  all Adnoc Distribution petrol pumps in the UAE. For the list of servicestations where ULG-91 be available, please click here: Service Stations
3. What will be the price of ULG-91 (E-plus)?

The price of ULG-91(E-plus) will be AED 5.75 per Imperial Gallon (IG).

4. What are octane ratings?

The octane rating of a gasoline is its ability to resist abnormal combustion. Two types of abnormal combustion are common: the first is detonation and the other is pre-ignition. Detonation occurs when the air-fuel mixture reaches a temperature and/or pressure at which it can no longer keep from self-igniting.

Detonation occurs after the spark plug has ignited the air-fuel mixture and the flame front is moving smoothly across the combustion chamber. If, during this burning process, the unburned air-fuel mixture reaches a temperature and/or pressure at which it is no longer stable, it burns very rapidly causing a new flame front to collide with the one that originated at the spark plug. Maximum pressure in the cylinder occurs before the piston reaches top dead center (TDC) and that pressure tries to push the piston down before it is ready to go down. As a result, Piston burning and rod bearing damage occur.

Pre-ignition is the other abnormal combustion and is usually started by a hot spot in the combustion chamber which causes the mixture to ignite before the plug fires. Under wide open throttle conditions, pre-ignition will destroy pistons in seconds.

Research Octane Number (RON)
RON is determined in a single cylinder variable compression ratio engine that operates at 600 rpm with a 125 degree inlet air temperature at standard barometric pressure. Spark advance is fixed at 13 degrees Before Top Dead Centre (BTDC). In a real world engine, RON is necessary to satisfy part-throttle knock problems.

Motor Octane Number (MON)
MON is determined in a single cylinder engine similar to the RON engine with a few changes that make operating conditions more severe and therefore the octane numbers are lower. The MON engine runs at 900 rpm with a 300 degree mixture temperature. Spark advance varies with compression ratio. In a real world engine, MON is necessary to satisfy octane demands at wide open throttle. This is a very important number for racing engines since they spend a high percentage of their lives under high speed and high load conditions. Racing engines cannot afford to be short on octane quality, since detonation or pre-ignition will quickly reduce a racing engine to junk.

ANTI- KNOCK INDEX - (R+M)/2
This is the average of RON and MON. It is sometimes referred to as the AKI or anti-knock index. It is the most commonly used octane reference today. It was developed about 20 years ago as a compromise between RON and MON for advertising purposes and also to keep from confusing the consumer with too many different terms. It has erroneously been referred to as road octane number.

Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades (RON): 91 octane, 95 octane and 98 octane. The ratings must be posted on stickers on each gasoline pump.

Adnoc Distribution's (RON) 91 Octane has an anti-knock index of 87.
5. Why is octane "sensitivity"?

The difference between RON and MON is called the sensitivity (RON - MON = Sensitivity). Because the two test methods use different test conditions, especially the intake mixture temperatures and engine speeds, then a fuel that is sensitive to changes in operating conditions will have a larger difference between the two rating methods. Our 91 fuel typically has a sensitivity of around 8.

Octane rating is in no way correlated with engine power or efficiency. There is more potential energy in a gallon of diesel fuel than a gallon of gasoline, yet the diesel fuel has a much lower octane value. 
6. What is "knocking"?
Knocking is the sound of abnormal fuel combustion. It is caused by abnormal combustion of the air-fuel mixture in the cylinder.

When a spark initiates combustion in a spark-ignition internal combustion engine, the flame front should fan out from the spark plug and travel across the combustion chamber rapidly and smoothly. If the last part of the air-fuel mixture ignites spontaneously before the flame front arrives, a sudden jump in the pressure in the cylinder occurs, creating the characteristic knocking or pinging sound. Knocking occurs because the octane of the fuel is below the antiknock requirement of the engine.

7. Is knocking harmful ?

Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.

8. Why do we need Octane Ratings?

The octane rating of the fuel reflects the ability of the unburnt end gases to resist spontaneous auto-ignition under the engine test conditions used.

To obtain the maximum energy from the gasoline, the compressed fuel-air mixture inside the combustion chamber needs to burn evenly, propagating out from the spark plug until all the fuel is consumed. This would deliver an optimum power stroke. In real life, a series of pre-flame reactions will occur in the unburnt "end gases" in the combustion chamber before the flame front arrives. If these reactions form molecules or particles that can auto-ignite before the flame front arrives, knock will occur.

If auto-ignition occurs, it results in an extremely rapid pressure rise, as both the desired spark-initiated flame front, and the undesired auto-ignited end gas flames are expanding. The combined pressure peak arrives slightly ahead of the normal operating pressure peak, leading to a loss of power and eventual overheating. This gives out the characteristic "knocking sound". The combination of intense pressure waves and overheating can induce piston failure in a few minutes. Under high-speed conditions knock can lead to pre-ignition, which then accelerates engine destruction.
9. What's the right octane level for your car?

Check your owner's manual to determine the right octane level for your car. 91 octane is recommended for many cars. However, some cars with high compression engines, like sports cars and certain luxury cars need 95 or 98 gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline. If your owner's manual specifies that your vehicle needs regular fuel, then there is no real benefit of using higher octane fuels. The only exception is if you are experiencing pinging or pre-ignition in your engine.

If you are not sure what fuel to use, start with the fuel grade specified by the manufacturer and keep track of your fuel economy. Then go up or down a grade of fuel. If fuel economy stays the same, then stay with the cheapest grade of the two. If fuel economy drops, return to the original grade of fuel. Even high performance cars can be driven with 91 grade fuel but only if the driver is aware that the vehicle should be driven sedately.

If you suspect that your vehicle's fuel economy has dropped off or performance is sluggish, try a tank full of a higher octane fuel. If the economy and performance improve, then you have likely been experiencing pre-ignition. Sometimes adjustments can be made to enable you to go back to 91 grade fuel, but if the problem is caused by deposits inside the engine, then using a higher grade fuel is suggested and could even be more economical by improving your fuel mileage.

Open the gas door on some vehicles and you will find a sticker that states "Premium Fuel Required" or "Premium Fuel Suggested". High performance vehicles have higher engine compression ratios and often operate hotter, both of which can cause pre-ignition to occur. Even though these vehicles typically use knock sensors to detect engine knock and protect the engine, you are probably better off to use the fuel specified.

Many drivers believe that using a premium grade fuel is better for their vehicle and produces more power. Not true. As long as the fuel does not pre-ignite, any grade of fuel will produce the same amount of power. Save some money at the pumps and optimize your fuel economy by selecting the correct grade of fuel for your operating requirements.
10. What other factors affect octane requirements?

Combustion chamber design, localized hot spots, piston speed etc. are some of the other factors that affect the octane requirement of an engine.
11. Will I get better performance from my car if I use a higher octane fuel like ULG-95?  

Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, Take note that if the recommended gasoline for your car is 91octane, then using a higher gasoline offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner. Your best bet: Listen to your owner’s manual.
12. Will higher octane fuel give me better fuel economy?

The possibility then to get more power out of a "premium" gas is very low. The higher price is not worth it.

Fuel consumption is determined by a number of factors: low-pressured tires, wind factor, outside temperature, remote starters, and most of all wild accelerations! Also a lot of people believe that gassing up with "premium" will give them more mileage per fuelling: "Gasoline with higher heating values give better fuel economy than those with lower heating values. There is generally only a small difference, about 2%, between premium and 91 gasoline. This difference traditionally favors premium gasoline but it can be in either direction."

13. Will higher octane gasoline clean my engine better?

As a rule, high octane gasoline does not outperform 91 octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine.  
14. Should you ever switch to a higher octane gasoline?  

A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the 95 will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.
15. What does a low Octane value mean, to me?

In the absolute worst case, if the fuel is too low octane, it may spontaneously ignite before the spark plug fires due to thermal rises from the heat of compression or from hot spots in the cylinder itself. This kind of ignition is called pre-ignition (as opposed to knocking) and will just destroy the engine.

What usually happens, and what we usually call knocking or pinging is that the fuel/air mixture does not ignite before the spark plug fires but does ignite spontaneously after that. The sparkplug fires and this causes an immediate, rapid, rise in combustion chamber pressure. This causes fuel on the other side of the flame-front to ignite before the flame-front reaches it. In turn, this causes combustion chamber pressure to rise even more rapidly. The result is an explosion inside the combustion chamber as opposed to the desired rapid burning.
16. What does a high Octane value mean, to me?

A high octane rating ensures that it takes a REALLY hot ignition source to ignite the fuel (such as a spark plug or the flame-front itself) and not just the rise in pressure & temperature that's a result of normal combustion. Note that the thermal rises in the cylinder are in direct proportion to the compression ratio of the engine. The higher the compression ratio, the higher the octane of the fuel that's needed.

Again, if the mixture in a gasoline engine ignites before the spark plug fires, we call that "pre-ignition." Pre-ignition can damage an engine before you finish reading this sentence. To reiterate, what we're really concerned with is called "knock" and that's the spontaneous ignition of the fuel-air mixture ahead of the flame-front as a result of the rise in cylinder pressure caused by the onset of ignition (caused by the firing of the spark plug).
17. Can higher octane fuels give me more power? Top

If you are already using the proper octane fuel, you will not obtain more power from higher octane fuels. The engine will be already operating at optimum settings, and a higher octane should have no effect on the management system.

On modern engines with sophisticated engine management systems, the engine can operate efficiently on fuels of a wider range of octane rating, but there remains an optimum octane for the engine under specific driving conditions. Older cars without such systems are more restricted in their choice of fuel, as the engine can not automatically adjust to accommodate lower octane fuel. Because knock is so destructive, owners of older cars must use fuel that will not knock under the most demanding conditions they encounter, and must continue to use that fuel, even if they only occasionally require the octane.

Your driveability and fuel economy will remain the same. The higher octane fuel costs more, so you are just throwing money away. If you are already using a fuel with an octane rating slightly below the optimum, then using a higher octane fuel will cause the engine management system to move to the optimum settings, possibly resulting in both increased power and improved fuel economy. You may be able to change octane between seasons (reduce octane in winter ) to obtain the most cost-effective fuel without loss of driveability. Once you have identified the fuel that keeps the engine at optimum settings, there is no advantage in moving to an even higher octane fuel. You may be able to carefully reduce the fuel octane.

 
18. Does low octane fuel increase engine wear?

Not if you are meeting the octane requirement of the engine. If you are not meeting the octane requirement, the engine will rapidly suffer major damage due to knock.

You must not use fuels that produce sustained audible knock, as engine damage will occur. If the octane is just sufficient, the engine management system will move settings to a less optimal position, and the only major penalty will be increased costs due to poor fuel economy. Whenever possible, engines should be operated at the optimum position for long-term reliability.

Engine wear is mainly related to design, manufacturing, maintenance and lubrication factors. Once the octane and run-on requirements of the engine are satisfied, increased octane will have no beneficial effect on the engine. Run-on is the tendency of an engine to continue running after the ignition has been switched off, the quality of gasoline, and the additive package used, would be more likely to affect the rate of engine wear, rather than the octane rating.

19. Can I mix different octane fuel grades? 

Yes, however attempts to blend in your fuel tank should be carefully planned.

You should not allow the tank to become empty, and then add 50% of lower octane, followed by 50% of higher octane. The fuels may not completely mix immediately, especially if there is a density difference. You may get a slug of low octane that causes severe knock. You should refill when your tank is half full. In general the octane response will be linear for most hydrocarbon and oxygenated fuels e.g. 50:50 of 91 and 95 will give 93.
20. What happens if I use the wrong octane fuel?  

If you use a fuel with an octane rating below the requirement of the engine, the management system may move the engine settings into an area of less efficient combustion, resulting in reduced power and reduced fuel economy. You will be losing both money and driveability.

If you use a fuel with an octane rating higher than what the engine can use, you are just wasting money by paying for octane that you can not utilize. The additive packages are matched to the engines using the fuel, for example intake valve deposit control additive concentrations may be increased in the premium octane grade.

You should initially be guided by the vehicle manufacturer's recommendations, however you can experiment, as the variations in vehicle tolerances can mean that Octane Number Requirement for a given vehicle model can range over 6 Octane Numbers. Caution should be used, and remember to compensate if the conditions change, such as carrying more people or driving in different ambient conditions. You can often reduce the octane of the fuel you use in winter because the temperature decrease and possible humidity changes may significantly reduce the octane requirement of the engine.

Use the octane that provides cost-effective driveability and performance, using anything more is waste of money, and anything less could result in an unscheduled, expensive visit to your mechanic.
21. How can I be sure if the 91 grade (E-plus) works in my car?

You can refer to your vehicle owner's manual, contact the car dealership or visit the vehicle list, You can also contact the Customer Interaction Center at 800ADNOC (80023662).
22. Do I have to tune my engine before using 91 Octane (E-plus)?

There is no need for any modifications in cars designed to use Premium 91.

23. Can I tune the engine to use another octane fuel?

In general, modern engine management systems will compensate for fuel octane, and once you have satisfied the optimum octane requirement, you are at the optimum overall performance area of the engine map. Tuning changes to obtain more power will probably adversely affect both fuel economy and emissions.

Unless you have access to good diagnostic equipment that can ensure regulatory limits are complied with, it is likely that adjustments may be regarded as illegal tampering by local authorities. If you are skilled, you will be able to legally wring slightly more performance from your engine by using a dynamometer in conjunction with engine and exhaust gas analyzers and a well-designed, retrofitted, performance engine management chip.
24. How can I be sure that the gas station attendant will fill my car with the required fuel?

The grades of petrol will be clearly labeled in all service stations. They will also have three different colors. ULG-91 (E-plus) is red in color, and ULG-95 (Special) is green in color and ULG-98 (Super) is blue in color.

25. What is the effect of engine speed?

Faster engine speed means there is less time for the pre-flame reactions in the end gases to occur, thus reducing the tendency to knock.

On engines with management systems, the ignition timing may be advanced with engine speed and load, to obtain optimum efficiency at incipient knock. In such cases, both high and low engines speeds may be critical, for more information please visit E-plus Technical Information page .

26. What is the effect of engine deposits?

A new engine may only require a fuel of 6-9 octane numbers lower than the same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to the formation of a mixture of organic and inorganic deposits resulting from both the fuel and the lubricant. They reach an equilibrium amount because of flaking, however dramatic changes in driving styles can also result in dramatic changes of the equilibrium position. When the engine starts to burn more oil, the octane requirement can increase again. ORIs up to 12 are not uncommon, depending on driving style. The deposits produce the ORI by several mechanisms:
  - they reduce the combustion chamber volume, effectively increasing the  
     compression ratio.
  - they also reduce thermal conductivity, thus increasing the combustion chamber
     temperatures.
  - they catalyze undesirable pre-flame reactions that produce end gases with low 
    auto-ignition temperatures.

27. What is the effect of air temperature?

An increase in ambient air temperature of 5.6°C increases the octane requirement of an engine by 0.44 - 0.54 MON.

When the combined effects of air temperature and humidity are considered, it is often possible to use one octane grade in summer, and use a lower octane rating in winter. The Motor octane rating has a higher charge temperature, and increasing charge temperature increases the tendency to knock, so fuels with low Sensitivity (the difference between RON and MON numbers) are less affected by air temperature.
28. What is the effect of humidity?

An increase of absolute humidity of 1.0 g water/kg of dry air lowers the octane requirement of an engine by 0.25 - 0.32 MON.
29. Where can I get more information about ULG-91 (E-plus)?

For more information on ULG-91 (E-plus) Please contact Adnoc Distribution Customer Interaction Center
 Tel: 800ADNOC (80023662)
Fax: +971 2 6945 666
e-mail: 800ADNOC@adnoc-dist.ae   
 
   
Conclusion

Check with the car maker's recommendations, you may find them written near the gas cap or in the driver's manual. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. If ULG-91 is suited to your car, it is the wise choice and you will continue getting the same performance from your car and also save money!
 

   
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