Petrol Quality/High Sulphur

Guys,

I new Tesco Petrol Station is being built in Tullamore and will be open after X-Mas. Does anyone have any experience of buying petrol from their other stations in Dublin, and is the quality on a par with other brands ie Esso, Maxol etc ?.

I'm just concerned with Nikasil, and high sulphur fuels. Do you think there is anything to worry about ?.

Ado 

It seems that all petrol now has to meet very strict standards, which include a very low sulphur content. Well that's what we hope anyways. I suppose the likes of Tesco's and other Supermarket retailers would draw more attention than your local street station, and would have to keep their standards high, as they would be checked more often.  

Just from listening to the guys in the UK on other forums, it seems that Supermarket petrols are  not the best quality. How high the sulphur content is I dont know. But the chances are if your car hasnt been affected by now , it probably wont be affected at all considering it only affected models from 95 to Feb 98.  If you havent noticed by 60k miles, i'd say forget about it.

Petrol in supermarket come from the same place as the petrol of the big brands. There is only so many reffinery in europe. The only difference is the additives, thats one of the reason why the tesco is a bit cheaper (less additives).

In france the main reason the the petrol to be cheaper in supermarket has nothing  (or very little) to do with the quality: while petrol station make living out off selling fuel, supermarket just try to get more people in their shop by using low petrol price as a "bite".

Regarding the fuel consumption, it has to do with the octane indice, the higher it is the less petrol you'll use. High indice mean greater explosivity, more power for your car. To go from A to B, you need a amount of work (energy), this amount is the same if you have diesel car, petrol car, if you use 95 or 97 octane indice. So you'll be using less diesel than petrol because diesel engine are more efficient and less 97 than 95 because each explosion is more powerfull with 95 than 97.

What is very damaging for diesel car is water in the petrol. The petrol leaving the reffinery all have the same water content, it's at the petrol station that it pick up moisture.

 

Sorry Ludo, your message came through as I was writing mine. You mention that supermarket petrol is refined the same as all other petrol, but they use less additives. Do you know what additives they use, and for what specific purpose ?.

So, the answer from a guy who spend is days designing reffinery for the middle east and asia:

All petrols have to comply with the same regulations for all their parameters:RON, MON, RVP, Sulfur, Aromatic coumpounds...

The additives are antifoaming agent, lubricant, RON booster.

Apparently one of the reason why you seems to fill like you're getting better fuel economy in petrol station is because the the antifoaming. When you pump the petrol in your car in the supermarket, as the petrol has less antifoam, it will foam (does make sense doesn't it?) more so the density of the petrol decrease so in fact you are putting less fuel in your tank (say for exemple you put 50L in petrol station and you let it settle you might get 49L once all the gas is gone whiloe if you take 50L in a supermarket you'll only get 47 or 48L)

Is the advice is go the supermarket an fill the tank slowly to reduce the foaming!

 

Yeah, i never knew that they put anti foaming additive in petrol, but I did understand that they put an additive in to prevent excess wear and tear to your engine. That's why I was worried about cheaper supermarket petrol which may not have all the additives.

It's amazing what you find out when you ask the right questions. Thanks Ludo.

ludo wrote: Regarding the fuel consumption, it has to do with the octane indice, the higher it is the less petrol you'll use. High indice mean greater explosivity, more power for your car. To go from A to B, you need a amount of work (energy), this amount is the same if you have diesel car, petrol car, if you use 95 or 97 octane indice. So you'll be using less diesel than petrol because diesel engine are more efficient and less 97 than 95 because each explosion is more powerfull with 95 than 97.

My understanding is that the RON figure does not reflect any calorific (energy) value - this only indicates its ability to resist auto-ignition, it is apparently less easy to ignite when the figure is higher.

Also, work is not the same as energy - energy includes the rate that work is done (i.e. time). To go from A to B, a certain amount of work needs to be done (and this varies from car to car due to mass, rolling resistance, friction, aerodynamics, etc.) - how fast you want to do this is then quantifies the energy. However there is also one huge factor in the energy consumed - engine efficiency.

Edited by b318isp

Firstly, gotta say, every day really is a school day!

As a non engineer, this may not be a valid observation, but my $0.02 worth is that the ron rating doesn't have an effect on the violence of the explosion (as per Brendan's explanation), but rather on the characteristics e.g. how soon the explosion begins after compression and spark have been applied, hence the fact that timing can be affected on cars when a lower or different ron rated fuel is used compared to manufacturer recommendation.  In most cases, cars with electronic ignition and fuel injection can adapt to that automatically. 

A difference in the violence (energy) of the explosion would suggest a difference in calorific value when maybe a difference in the characteristics of the explosion would be more accurate?

If there is ignition before TDC then the piston will start to be forced back down prior completing the full stroke and being on its downward track, hence loss of power as crank momentum is lost in overcoming this force.

Heres another one or two for homework on the weekend.  No excuses from anyone now. 

http://www.mg-tri-jag.net/tech6.htm 

http://www.camshafteng.com.au/calc.htm