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On a higher octane
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Why does expensive fuel mean a better deal?
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By now you must have seen the various advertisements from petrol companies trying hard to tell you why a certain brand of petrol is better than the usual stuff. If you are seriously thinking of buying these expensive fuels, then forget all the marketing gimmickry and pay attention to the octane rating of each brand.
But what exactly is octane rating? Essentially, this is an index based on two methods of testing fuel. The research octane number (RON) is a calculated number, while the Motor octane number (MON) is a measurement of a pre-detonation resistance in an actual research piston engine. Add RON and MON and divide by 2 you get the octane rating of any fuel. Why do you need higher octane petrol? Firstly, you might need it to prevent your car's engine from knocking. Knocking or pre-detonation occurs if portions of the unburned air-fuel mixture at the edges of combustion get compressed against the cylinder walls and explode before the actual wave of the flame-front gets to them. These unwanted detonations physically rattle the cylinder walls and cause the knocking sounds you hear. To be effective, maximum pressure in the combustion chamber, caused by the expansion of burning fuels, must reach just as the piston reaches the top of its upward travel. During knocking, maximum pressure is reached much before the piston gets to its top position, thus effectively applying downwards pressure on the piston while it is still moving up. This obviously causes a loss of energy as well damages the piston rings, bearings and even the piston itself. Much of the engine's energy is lost as a result of this.
The higher the compression of an engine, the higher its `octane requirement' and the more power it makes. But does it make any sense to put in higher-than-specified octane fuel into you car if your engine isn't knocking? Logically speaking, no. But real-world conditions are different. Factors like the deposits of carbon and drop in octane at petrol pumps play a role here. In fact, a number of studies have shown that cars that have done between 30,000 and 50,000 km could require additional octane, unless you decarbonize the engine regularly by using fuels like Speed and Power.
We tested fuels using a Honda City, a car with a comparatively high compression engine ratio of 10.5:1. The car was run on two types of fuels - 87 and 93 octane. As if to prove the point, the City performed much better with octane 93, 0.57 seconds quicker in a 0-100 kph run on the higher-octane fuel. Using higher-octane fuel, we also noticed that the engine fired the spark plug earlier for better power and performance.
Overall, the best way for you to ensure that your engine does not knock is to use petrol with detergents in them (like Speed and Power). This in turn lowers the engine's octane rating by clearing out a lot of carbon deposits that lead by knocking in the engine. Also a point to remember here is that the octane number requirement is reduced if you have an aluminium head, as it is a better conductor of heat and runs cooler. So the next time, remember to tank up with higher-octane fuel. It's certainly more expensive but will ensure the engine will enjoy a longer, happier innings.
ASHISH MASIH
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