Do you want the Road Tax system to change? Do you have thoughts on the potential changes to the Road Tax system? | No thanks
Ultra low sulphur petrol - Ian Seth
Most garages now sell ultra low sulphur fuel. My fuel consuption seems to have increased by up to 5% since it's introduction. Is this normal?
Re: Ultra low sulphur petrol - John S
Ian

Previous threads on this site have indicated that some contributors have thought the same, but not all. Don't forget a number of factors affect fuel consumption. Particularly, it's recently got much colder and that always increases fuel consumption. You'll need to check this for a while to be sure it's definitely the fuel.

It does seem a little strange, as there should be no change in calorific value due to the lower sulphur.

regards

John
Re: Ultra low sulphur petrol - RogerL
I'm not aware of technical reasons why fuel consumption should be any different on ultra low sulphur fuel. When catalytic converters were introduced, cars left a smell of rotten eggs until warm if using high sulphur fuel but this fuel didnt provide better fuel consumption. Crude oil has always varied considerably in sulphur content, North Sea being low, Middle East being high. I don't think that sulphur is beneficial or harmful to the engine, it's just undesirable in the atmosphere.
Re: Ultra low sulphur petrol - Julian Lindley
John S,

I'm intrigued by your reply to Ian re fuel consumption and cold ambient temperatures. Although an assumption on my part, I have taken the view that a low ambient temperature encourages a greater air mass to be drawn in per induction stroke, and that this would improve combustion efficiency.

I admit that engine operating temperatures may be slightly lower, but would they be significantly lower with todays intake and thermostat systems?

When I heard of the trend towards better fuel consumption with higher sulphur content fuels, I thought that this must relate to a higher calorific value for this fuel. If its the same and MPG is greater with it, Where on earth can the benefit be coming from? A "Q" for a fuel company in the new year I guess.

All the best,

Julian
Re: Ultra low sulphur petrol - Julian Lindley
John S,

I'm intrigued by your reply to Ian re fuel consumption and cold ambient temperatures. Although an assumption on my part, I have taken the view that a low ambient temperature encourages a greater air mass to be drawn in per induction stroke, and that this would improve combustion efficiency.

I admit that engine operating temperatures may be slightly lower, but would they be significantly lower with todays intake and thermostat systems?

When I heard of the trend towards better fuel consumption with higher sulphur content fuels, I thought that this must relate to a higher calorific value for this fuel. If its the same and MPG is greater with it, Where on earth can the benefit be coming from? A "Q" for a fuel company in the new year I guess.

All the best,

Julian
Re: Ultra low sulphur petrol - RogerL
The greater mass of cold air drawn in is compensated by additional fuel being injected (on a modern engine). The increased fuel consumption comes from greater air resistance because the air is denser.
Re: Ultra low sulphur petrol - Julian Lindley
Roger,

I guess that you are talking in this case about the additional energy a car requires to drive through cold dense air. I learn something new on this site every day. It has never occurred to me that colder days, as a result of an increase in air density, would diminish a cars fuel consumption. I had always taken the view that the improved air charging during engine induction would be a bonus.

Regards,

Julian.
Re: Ultra low sulphur petrol - John S
Julian

I've always attributed the higher winter fuel consumption to:

Longer warm up times, so longer periods spent on richer mixtures
Greater drag due to colder engine and transmission oils - not only from cold, but also during 'normal' operation.
Greater use of electrical accessories
More use of the car for short trips 'because it's cold'

Roger's right that modern cars will compensate for air mass, but the problem persists with carb fed cars.

regards

John
Re: Ultra low sulphur petrol - John S
Julian

Should have said 'air density' of course! Must be the results of yesterday's celebrations! I'm trying to work out whether increased air density would affect carb fed cars - I've certainly found in the past that they can be a lot worse on fuel in winter, but don't know the primary cause. Rarely use the Minor in Winter, so can't really check.

Greater air density will increase drag on the car, but whether this is significant I'm not sure.

Another winter affect will be that colder tyres will also increase drag


Regards

John
 

Ask Honest John Right column

Value my car