premium fuel or normal fuel

Hi friends, I endorse Rohit's views, ordinary fuel upto cars like Corolla is absolutely fine, I used premium but there was knocking, I started using ordinary fuel, the same is running absolutely fine. I do not have anything against premium fuel, the cars in Indian condition are fit for ordinary fuel.

@justin - Hyundai "recommends" - and its just that. Ordinary fuel should work just fine...there are occasions when pumps run out of ordinary petrol and offer only speed/premium, I guess at such times no harm in filling up on that if you really cannot wait (or fuel level is really low).

@Kapil - I don't understand why you got knocking with premium fuel. For one, a normally working (i.e., one without any problems) engine knocks if the fuel's octane rating is (considerably) lower than what it was built for. In your case this makes me suspect that the premium fuel is actually lower in octane rating than ordinary fuel - there's no other explanation if the engine is in top condition. The only advantage of lower octane fuel is that its better to be used at high altitudes where the air (and hence oxygen) is rarer as it mitigates engine stalling or loss of power due to less availability of air (and hence loss of compression related power reduction). That said, is this what our Indian premium fuel makers intend when they ask us to put speed or premium fuel into the tank?

Rohit - a lateral-thinking explanation comes to mind - There are additives in the premium petrol for the engine to run extra smooth => more room for adultration => Sometimes the adultrators exceed mandate => premium fuel is worse than ordinary fuel => knocking with premium but smooth run with ordinary, exactly contrary to expectations!

Hi Rohit, the same discussion I had at length with the General Manager of Deep Hyundai, New Delhi for my brand new Hyundai Accent, he told me that the normal engines are meant to ignite at the specific level, by fuelling premium oils, they tend to ignite before the actual rotation completes resulting in the knocking from the engine.

He further added that its the premium fuels which are more contaminated than the ordinary ones, therefore, its better to use ordinary fuels, infact, I have been told that the life of the fuel pump for that matter is affected with the usage of premium 93+ octane fuels.

i agree with the views of Krishna but that's only one part of it, second, how early the fuel ignites the engine which I mentioned earlier.

Hmm...that explains why - premium fuels probably contain octane reducers to improve performance (and isn't that what they claim - Improvement in performance?). And how will you improve an engine's performance without actually opening it? Use lower octane fuel - yes and none of the premium fuel makers claim any sort of octane boosting (at least not explicitly)!!

Friends - you are having it arse-backwards - Knocking is something of a result of premature ignition of fuel. Please read this Wikipedia entry

If the fuel auto-ignites, it does so when the compression stroke is going on - the piston has not reached the position of maximum compression. For smooth operation, the fuel should ignite such that the expanding gases act on a retreating piston - that way the cranking of the crankshaft is in the same direction.

The autoignited fuel pushes the compressing piston in the opposite direction, resulting in a violent back-thrust to the crankshaft. This could potentially upset the whole mechanism, and result in a stall.

Higher the octane, less the tendency of the fuel to autoignite, so that the sparkplug ignites the fuel at just the desired crank angle.

This morning I refuelled at an Indian Oil pump and casually asked the attendant serving me whether they had System G. He was completely blank and doesn't even seem to have heard about it.

Try some shops that sell engine oil etc.

Hi all,

We should use normal Diesel/Petrol only.....kk

I would rather add to KK only if the user manual specifies the specific usage of the premium oil, then only, else, normal petrol/diesel is absolutely fine.