I was wondering what uses more fuel on a diesel engine.
Heavy footed acceleration
Driving at 100mph (engine revs high)
or
Driving with too high a gear for the speed (labouring the engine)
Which one?
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Insufficient data. If you're interested in saving fuel, avoid the first two.
The last one isn't really a problem from a fuel perspective. Leaning towards torque demand rather than higher revs is broadly beneficial, though power demand is the overriding factor. But more unpredictable in its effect on the DMF perhaps.
Last edited by: Manatee on Mon 27 Sep 10 at 19:18
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Trick is, in my opinion anyway, to buy a car which achieves a fuel economy you can afford or can live with averagely. Then you don't have to bother adapting your driving style at all. You just drive it and don't worry about the mpg.
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I just wondered as the above listed conditions are what I certainly do NOT want to do.
certainly not on my nice car, hence the questions.
Last edited by: diddy1234 on Mon 27 Sep 10 at 20:12
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My experience with trucks has shown me that driving with as low revs as the engine/transmission can comfortably take is by far the most economical, higher revs leading to full turbo pressure can put fuel through at a tremendous rate.
I think you will feel if the revs are too low to be safe, but low revving touring type driving can be extremely pleasant in a Diesel.
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A diesel engine runs at full airflow all the time - the accelerator pedal controls the amount of fuel being injected, unlike a petrol where the accelerator pedal adjusts the airflow. Most modern diesel cars operate a "drive-by-wire" system, where even when the pedal is fully depressed, the ECU will only allow the appropriate amount of fuel for the engine speed/load to be injected.
Trucks are a little different, unless a truck driver is accelerating full-bore and braking as hard as possible everywhere I can't see how driver behaviour will make much difference to their economy. GB - all the trucks I drive have a "green band" in the middle of the rev counter, I change up at the top and down at the bottom, don't all drivers do that? :)
Last edited by: Dave_TD {P} on Mon 27 Sep 10 at 23:56
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all the trucks I drive have a "green band" in the
>> middle of the rev counter, I change up at the top and down at the
>> bottom, don't all drivers do that? :)
>>
They don't as you well know D -:), there's some truck drivers out there that haven't got a clue how to get the best economy from a Diesel whilst still making reasonable progress.
I've been passenger in some (that can be fun following 10 ft from any and every vehicle in front) that only venture into the green when in top gear at governed maximum speed, and the second that they meet a hill will drop a cog which inevitably means slower hill climbing and more changing as they are constantly above peak tourque, you could explain forever and it will never sink in.
It's eye opening watching the instant fuel consumption readouts, top gear under load will see it at 3.4mpg, drop a gear and it will drop to 2.6 or so and still in the green band.
I drive one make that really does improve by overriding the auto box and i regularly get consumptions of 13.8 to 14 mpg over a days work with 15 mpg quite achievable on purely motorway work, that's by keeping the revs between 900 and 1300 where auto will see 1700 often before changing and at junctions where this particular box in auto doesn't do at all well.
No different to cars in my humble.
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What make and at what weight, GB?
Pat
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>> I drive one make that really does improve by overriding the auto box and i
>> regularly get consumptions of 13.8 to 14 mpg over a days work with 15 mpg
>> quite achievable on purely motorway work, that's by keeping the revs between 900 and 1300
Surely that's just a four wheeler rigid at that MPG?
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Pat and a900.
Pat will already have guessed which make, i doubt anything else could touch it.
Scania 420 artic unit with high ratio diff, something like 1000rpm at 50mph, weight carried is pretty light though, 5 axle non tag combo so probably 14 to 15 tons empty but only carrying about 4/5 tons load.
I also drive these sometimes for another haulier running groupage, so not always max weight, probably 15 ton loads, usually between 12.5 and 13 over a day depending on number of drops and terrain etc.
I had one of these Scanias as a car transporter, much heavier circa 23 tons empty, but even running empty (and negligible wind resistance through the rigging) i couldn't get any better than 10.5 at a constant 50mph motorway running...though the gearing was all wrong (typical) around 1450 rpm at 54mph and they seemed to be derated power wise, presumably in a futile effort to save fuel whch they did with another make...that worked the wrong way too.
Edit, these figures are from the onboard fuel computers, which should be accurate but who knows.
Last edited by: gordonbennet on Tue 28 Sep 10 at 17:04
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...high ratio diff, something like 1000rpm at 50mph...
Must get one of those for the CC3 - it would do 220mph. :)
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I knew you would be running light:)
The HR Diff does make a lot of difference.
We had a fuel bonus introduced based on manufacturers fuel figures for running to weight, it should have paid both the drivers well in wages and the firm well in fuel saving.
Three months later it was abandoned because despite fuel efficient driver training, no-one could get near it.
Those that tried it caused late delivery penalties for our famous supermarket RDC deliveries ( which are JIT) so someone sensible realised fuel saving isn't the end of the story:)
Pat
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...RDC deliveries ( which are JIT)...
Pat,
Look, we quite like your lorry chat, it brings an extra dimension, but could you please allow for those of us who are not in the trade?
RDC? JIT?
JIT, I'll wager is 'just in time', but the other one's got me stumped.
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Regional? Distribution Centres. perhaps?
(regional could be retail heard both in use - basically the biggest automated warehouses you have ever seen)
You need more training in FMCG
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Sorry Iffy:)
Yes JIT is Just in Time.
It means that a normal traffic office plan loads for each veicle 48 hours ahead, but if you deliver the the Regional Distribution Centres they have a 24 hour leeway to drop 1 (or 2) pallets into every RDC they have with a booking time of their choice.
This is why most traffic planners and TM's are bald. They tear thier hair out trying to fit another couple of pallets on a lorry that is already full and has 10 deliveries on it with booking times already agreed.
There are usually financial penalties for not making JIT deliveries,
too so guess who gets the late deliveries!
The problem comes when we are situated in Cambridgeshire and Morrisons at Bellshill need one pallet booked at 7am the next day, the lorry is still loading it in the yard at 2pm, and needs at least 9 hours off and 8.5 hours driving to Bellshill.
Fuel consumption becomes less important then.
Pat
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The first time I came across JIT was in connection with the Nissan plant in Sunderland, Tyne and Wear.
I read somewhere they give each delivery of components a 30 minute slot which has to be met, or there are financial penalties.
Of course, if you order a new Qashqai, they will make it when it suits them, so what's sauce for the manufacturer goose, is not sauce for the customer gander.
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It's exactly the same.
If you're early they won't let you in. If you're late they fine, you but when you're on time they can keep you in there for anything up to six hours to tip one pallet without penalty, making you late for everyone else.
Remember the old adage 'When the wheels ain't turning the vehicle ain't earning'.
Pat
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based on manufacturers fuel figures for running to weight,
>> it should have paid both the drivers well in wages and the firm well in
>> fuel saving.
I was having a chat with a transporter driver from another company, despite retraining they can't get the 11 mpg overall that someone told them they could..;)
Wrong gearing and same set up as i had on my previous job, in real world saintly driving they'll struggle to average 8.5 overall.
What's that, a politicians promise?..;)
Anyway Diddy we nicked your thread, sorry matey, but it's all the same thing and size doesn't matter (good job too) careful progressive driving not necessarily slowly but not tearing about for good fuel consumption and long vehicle life.
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No problems, quite an interesting read.
Why don't the car makers fit a green eco strip on the rev gauge like in the above lorry's ?
Us drivers would have something to aim for then.
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...Why don't the car makers fit a green eco strip...
Some petrol cars had an 'economy' gauge, or sometimes three lights: red, amber and green.
I think it was based on inlet manifold pressure, so a light throttle opening would give a green reading.
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Racking me tiny mind here, has there ever been a Diesel car with a green economy band on the rev counter, if not why not.
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Fuel costs used to be very important to me. They still are of course but less acutely so now that someone else is paying for my business fuel. Over the years though I have tried to drive economically sometimes and not bothered on others. I figured out that the potential savings to be gained by driving around like a funeral director were about 2p a mile. Even if times are unusually hard, life really is too short to worry about sums like that.
All vehicles have a sweet spot in their performance. Some are natural motorway bashers, some are happier in the cut and thrust of urban driving, some are at their best when faced with the challenges of a twisting winding country road. ( of course Mondeos can do all of these things with aplomb ) Far better to drive the vehicle as it naturally wants to be than to be pussy footing around trying to save a couple of pence a mile.
Any one of us might snuff it tomorrow. You wouldn't want to be lying there on the trolley looking at your toes for the last time thinking how clever you were to save £200 quid on your diesel bill last year would you for Pete's sake ! You might though, decide that you rather enjoyed that drive last week...
Anyway. Pah !
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diesel engines - what uses more fuel - Manatee
