Fuel Economy Reporting Thread

alcale

I used to drive my diesel at 90mph on motorways, but by slowing to 70 my fuel consumption was cut almost in half, from 350 miles per tank to 600 miles per tank.

The extra travel time isn't that much - 20 mins per 100 miles.
100 mile trip @ 90mph = 67 mins
100 mile trip @ 70mph = 87 mins

Also, biodiesel is cheaper - buy it for around 80p a litre, or make it using cooking oil from a local take-away for next to nothing (although you do have to pay the Revenue 27p per litre in fuel duty). Never tried making it myself, but plenty of websites tell you how. Seek advice before sticking it in your car though!

al

Conor_3

anewman wrote: »

Wynns and other companies sell fuel injector cleaners. I tried some and noticed a slight difference in performance but couldn't tell whether it improved MPG. My guess is it didn't.

They actually do because they clean the carbon and varnish off the injectors which results in a better spray pattern (better dispersal gives improved burn) and an injector that shuts fully so it's not dribbling fuel when the engine isn't in the induction cycle.

Conor_3

john_of_leeds wrote: »

I started to turn the engine off and coast to a halt and not restart till red and amber i saved on average of at least 15-20% now i am on ordinary driver i coast on the flat and downhill and still achieve good savings.I know its illeagal i think to coast but that was when we had crash boxes and poor brakes now we can have at least 5 applications of the brake before the servo vacuum depletes.

Why the hell would you do this? Modern fuel injection engines and diesels since the dawn of time shut off fuel completely on engine overrun - i.e when you take your foot off the accelerator as you slow. You'd only gain if you had an engine with a carburettor which counts out any petrol engined vehicle made after 1992. All you are doing is breaking the law and not having full control of the vehicle for no reason whatsoever.

kaya

Ive spent the last year building a fuel saving/emissions cutting device, its not snake oil, im not even gonna tell you who is marketing it, but it works, we have run 3 independant tests with different hauliers and are getting between 17 and 25% economy, the technology is out there and does work, but there is also a lot of rubbish, magnets, bent bits of wire, pills in the tank etc.., my point is measuring your fuel economy is not something the likes of us can do accuratley, put a pint of cold diesel oil in a bottle , heat it to 30 degrees c and see how much it expand in volume, now think you have 50liters in your tank, multiply that expansion in volume by the 50liters and you can see how your calculations can be out, best advice is keep your tyres at the correct pressure, change up through the gears as soon as possible keeping the rpm low, dont carry around a ton of junk you dont need in your car, keep a good distance between you and the car in front, travel when there is less traffic if possible, keeping your windows done up can show a 5% increase believe it or not, and keeping the air conditioning off, for any petrol heads there is a company in norfolk called trident who build a 200mph diesel supercar called the trident icini which returns 70mpg, they drove it from norfolk to monaco on one tank of bio diesel made from rapeseed oil!, if they can get that economy and performance from a car dont you feel a little undersold by the big car manufacturers?

Conor_3

And who are these hauliers, Kaya? Just interested to know seeing as I'm in haulage and I can't recall seeing anything in the haulage press about it.

shimmyshack

as said by roodenberg, ashbolt and particularly alcale, the point is your
SPEED
simple as that.

wind resistance (the force you expend fuel to overcome) increases with the square of speed,
so if you go at a steady 50 instead of 100 on the motorway, you use 4 times less fuel (2 squared)

All other methods are just window dressing.

The other day I drove from Basingstoke->Birmingham->Basingstoke, at 55mph in a 8yr old 1.6 petrol estate at 60mpg, total cost £20.90p

Driving at 55mph instead of 70mph halves your fuel bill, but only adds 12 minutes per hour to your journey time, it halves your carbon footprint, decreases the risk of an accident and the consequences of any accident that does occur, and lowers your blood pressure. (while slightly increasing others admittedly!)

I'm no tree hugging liberal, but it's all good!

Conor_3

shimmyshack wrote: »

wind resistance (the force you expend fuel to overcome) increases with the square of speed,
so if you go at a steady 50 instead of 100 on the motorway, you use 4 times less fuel (2 squared)

.

Rubbish. On the economical driving course I did, a graph of speed vs wind resistance showed a fairly constant resistance until you got to 55MPH where the resistance then increased exponentially.

shimmyshack wrote: »

Driving at 55mph instead of 70mph halves your fuel bill,

Most of which is attributable to the fact you can maintain a constant 55MPH whereas something will inevitably get in your way at 70 and require you to slow.

shimmyshack

"wind resistance goes as square of speed"
anyone who needs confirmation of this well known rule, need only look as far as
http://en.wikipedia.org/wiki/Drag_(physics)
(see the secton on drag at high velocity)
"Assuming a constant drag coefficient, drag will vary as the square of velocity."

Not many cars I know of change shape as they increase speed, consequently they do indeed have a constant drag coefficient.

A graph of force vs velocity that increases exponentially - now /that's/ rubbish

twowheelspete

shimmyshack wrote: »

"wind resistance goes as square of speed"
anyone who needs confirmation of this well known rule, need only look as far as
http://en.wikipedia.org/wiki/Drag_(physics)
(see the secton on drag at high velocity)
"Assuming a constant drag coefficient, drag will vary as the square of velocity."

Not many cars I know of change shape as they increase speed, consequently they do indeed have a constant drag coefficient.

A graph of force vs velocity that increases exponentially - now /that's/ rubbish

yep

and accelerating hard in a fuel injected car is dandy as the ecu keeps an eye on things. On a carb'd car (not many of 'em around today) I'd be surprised if it were more efficient to floor it.

I ride a motorbike and if I accelerated hard all the time, the tyres would just wear really quickly. The very same is true of cars but to a lesser extent.

epninety

twowheelspete wrote: »

and accelerating hard in a fuel injected car is dandy as the ecu keeps an eye on things. On a carb'd car (not many of 'em around today) I'd be surprised if it were more efficient to floor it.

Wide Open Throttle is the one time when most efi systems don't much outperform a well set up carb. The ECU has to go open loop (ie not use the lambda sensor to control fuel mixture) because the mixture needs to be rich to increase power safely and the lambda sensor can't tell *how* rich the mixture is. For this reason the ecu drops back to a lookup table in this situation, so it's not doing much more than a carb could do, except a small compensation for air temperature

Of course, you need to find a well set up carb to do the comparison (over there, under that pile of hens teeth). :rolleyes:

There are a few cars that can accurately measure the air/fuel mixture with a special lambda sensor, but they are pretty rare (special lean burn setups)