Possible economy tip, or daft?

[simonr]

You beat me to it -

If the photos are anything to go on, you are testing a fixed fan (no viscose coupling) and mechanical water pump against none. That is not comparable to an engine running at 2-3000 rpm with a viscose fan.

Although measured mpg does not have the immediacy of a dyno, if you assume the measurement accuracy is say +/- 10%, any change between viscose and electric over a few thousand miles is hidden. The difference between with & without over the same number of miles was within 1%. Sometimes electric did better and other times viscose - but because of the error margin, I could not say either returned greater efficiency.

Next.

RecklessEngineer - you are confusing engine load/rpm with road speed. Even from your graphs, it appears that the best efficiency is attained at 900 rpm, 80% load. At 900rpm, even if 5th, my LR is going fairly slowly!

The freelander is a good test case because the efficiency of the drive is fairly similar regardless of the speed. High currents reduce the effective battery capacity (Purkett effect) - but I was measuring the energy going in to the motor so that's irrelevant.

The freelander shows that the viscose drag, moving through the air and the roll resistance of the vehicle, both increase with speed. Above 50mph, there is a knee in the curve and the rate of increase changes from largely linear to geometric. This is the point where the aerodynamic drag becomes more significant than the roll resistance.

Both your graphs, and my findings indicate that (from your data, so long as you can keep 80% load and low RPM) lower speeds will achieve better mpg!

Si

[Tanuki]

Cylinder-deactivation is quite common on modern large-engined cars: they do it with hydraulic valves that stop the pairs of valves opening on some of the cylinders. It's a bit smarter than that though - the "deactivated" cylinders are cycled round so if a cylinder has been deactivated for one firing-cycle it will be reactivated for the next engine-rotation - the reason being to keep all the cylinders at a uniform temperature internally.

Some of the first-generation cylinder-deactivation systems were horrid though: the 1980s Cadillac V8-6-4 singlehandedly set the very idea of cylinder-deactivation back by a couple of decades.

Reducing wind-resistance and weight are the best ways to get economy, followed by reducing rolling-resistance.

Do you actually need that roof-rack or the light-bar mounted on it? Can you move the spare-wheel off the bonnet and stow it inside the vehicle where it's not going to disrupt the airflow? That farm-jack and winch may look nice bolted to the outside but they're adding a couple of hundred pounds of extra weight you need to burn fuel to haul around. Suspension lift - that's going to cause more air-drag, and 'knobbly' tyres on big rims weigh more as well as creating more friction with the road.

[Hint: even OEM alloy wheels often weigh more than the steel-wheel equivalent option.].

Colin Chapman, the guy behind Lotus cars, would often look at a design produced by one of his engineering-tram and tell them "OK, brilliant - but now add lightness". The story is told of one of his "John Player Special" Formula-1 race cars where he looked at it and got the designer to cut out several 'unnecessary' pieces of chassis to save weight, despite the designer's vocal protests.

Some weeks later the car "broke its back" while being wheeled onto the transporter.

"Told you so!" said the engineer smugly.

"We won the race! That's all that matters!" said Colin with even greater smugness.

[TheRecklessEngineer]

RecklessEngineer - you are confusing engine load/rpm with road speed. Even from your graphs, it appears that the best efficiency is attained at 900 rpm, 80% load. At 900rpm, even if 5th, my LR is going fairly slowly!

Both your graphs, and my findings indicate that (from your data, so long as you can keep 80% load and low RPM) lower speeds will achieve better mpg!

Si

Certainly, I don't disagree with lower speeds requiring less energy for the same distance. The graphs are some I nicked from the internet and have no relevance to an LR engine other than the fact that all diesels have a similar curve. It is in fact for a generator - that tops out at 1000rpm. The left hand graph is largely irrelevant.

If you're heading for a hill it'll take a fixed amount of energy to get you to the top. If some of it comes from momentum then that energy must be replaced to get you back to your cruising speed. The most efficient way of getting that energy out of the engine is by sticking your foot down to get yourself onto that 80% load point where your engine will have it's maximum efficiency.

Perhaps the argument is academic as the longer time spent at a higher speed might outweigh any efficiency savings from running your engine at a better load point. Putting that another way - any savings made by going slowly up a hill are coming from spending a longer time at a slower speed (under your cruising speed) rather than any efficiency savings in the engine.

The same argument holds true for acceleration as well as hills.

[snailracer]

I've found with my 200tdi that it wont overheat on a long run without a fan at all. I've thought about fitting an electric fan but as i've never managed to get the needle over N i've never bothered....

I get about 29mpg mainly from short journey driving (<5 miles). 200tdi, overdrive, road bias tyres, no extraneous carp. It is however a softop pick up so probably doesn't weigh very much (relatively)

[Aragorn]

RE the peak BSFC, as mentioned above the graph posted is a medium speed diesel generator engine. A car engine will have a similar graph, but peak BSFC is typically near peak torque.

Heres a graph from a VW 1.9TDI:

As you can see, peak efficiency is right on the torque peak.

Lower RPM's dont suffer too badly so long as your above about 1200rpm

Interestingly i was reading something the other day about a hypermiling technique called "coast and burn", which involves accellerating upto a speed (say 35mph) then declutching (and even shutting the engine off at the extreme end) and letting the car coast down to say 30mph, before re-engaging the engine and powering back up to 35 again.

The idea being that the engine spends most of its time at high load and thus high efficiency sites, and improvements of around 30% can be seen in town style driving.

[ThreePointFive]

All this talk of cylinder de-activation, torque curves, fancy graphs....

Just wind the accelerator stop out a bit and have done with it.

[zoltan]

Is that with a fixed fan rather than viscous?

Yes fair enough, a bit of an apples and pairs comparison. I was trying to show the impact it's removal would have on the engine which you couldn't possibly gauge in road driving as you'd never replicate the driving conditions and achieve measurement repeatability that you can on a dyno. I'll go and sit back in the corner

[Yostumpy]

RE the peak BSFC, as mentioned above the graph posted is a medium speed diesel generator engine. A car engine will have a similar graph, but peak BSFC is typically near peak torque.

Heres a graph from a VW 1.9TDI:

As you can see, peak efficiency is right on the torque peak.

Lower RPM's dont suffer too badly so long as your above about 1200rpm

Interestingly i was reading something the other day about a hypermiling technique called "coast and burn", which involves accellerating upto a speed (say 35mph) then declutching (and even shutting the engine off at the extreme end) and letting the car coast down to say 30mph, before re-engaging the engine and powering back up to 35 again.

The idea being that the engine spends most of its time at high load and thus high efficiency sites, and improvements of around 30% can be seen in town style driving.

The 'coast and burn' technique is more commonly called ' pulse and glide' . any reasonable downward hill, hard short burst at the top, knock it out of gear and glide down the otherside as far as you can. I've fitted a 'kill switch' for t/lights etc. Tyres are pumped up, windows shut, etc etc. Driving up hill, you effectively set the gas at the bottom, and keep it there, and not add any more, you'll hear the engine note change , much deeper, as its working hard with what its got, this is known as DWL, 'drive with load' , then there's DWB,, 'drive without brakes' not literally but anticipate so you don't touch them.

After my pump was tweaked by Van Aaken 5 years ago the milage actually went down slightly, initally I was goofing around having a bit of fun, but it was prob 1 mpg lower than before, even tho I didn't drive it hard at all,

Q. Interestingly , if there are 2 routes of similar distance from a to b, route 1 is flat, and route 2 is 'hilly', which one is the most economical one to travel (for the experienced hypermiler.)

The way to accerelate , as per the BSPC graph, is n't gentle at all, its quite hard up to 1800-2000rpm, change up and same again, the back off at the cruising speed. This is for a TDi motor, not necessarily petrol.

There are many Hypermiling techniques, and I'm interested, not becaiuse I cannot afford to run my truck, but because it is a challenge.!! Hence my original post, about getting up to speed, then shutting off part of the boost pressure. Sometimes thinking 'outside the box ' is good. sometimes not. It is pleasing to get a good many sensible answers, from technically minded individuals, rather than ' why don't you get a ....'

A. The answer by the way, as you prob have guessed by now is ,,,,,,,,,,,,route 2

[Aragorn]

Yeh, I tried the pulse and glide thing around town in the A4, and at least as far as the fuel computers concerned it defo seems to work, and it doesnt even have to be particularly hilly, the cars momentum means it rolls for a fair distance on the flat before its slowed down by 5mph and you want to be getting back on the power. While gliding the fuel computer registers "200mpg" as its instantaneous consumption, though i suspect its actually higher than that, and 200 is just the upper limit of what it can display, and the average from a drive across town does seem to increase by a couple mpg. It takes a lot of care though, as its a turbocharged petrol, so anything resembling a bootfull sees the fuel consumption drop into single figures.

Problem is it doesnt take long before someone tinkles me off and i'm forced to deploy full throttle, so i've never kept it up long enough to see measureable fuel savings.

[Dan110]

While gliding the fuel computer registers "200mpg" as its instantaneous consumption, though i suspect its actually higher than that, and 200 is just the upper limit of what it can display

Would I be right in thinking that modern cars burn no fuel at all while on the overrun? I'm sure I heard that from someone reliable! I assume if true, it wouldn't apply to a 200tdi?

[Aragorn]

On overrun yes, trip computer in the A4 says "---" however the vehicle slows down pretty quickly due to the engine braking.

Coasting as mentioned above has the clutch disengaged, so the engine drops back to idle and uses a small amount of fuel to keep it idling, while your rolling forward with momentum alone.

[Dan110]

Got you, thanks.

[TheRecklessEngineer]

Would I be right in thinking that modern cars burn no fuel at all while on the overrun? I'm sure I heard that from someone reliable! I assume if true, it wouldn't apply to a 200tdi?

Certainly does apply on a TDi. Even my ancient 6hp Lister CS will go to no fuel on overrun. The injection pump has wizardry inside it to make this happen. Carburetted engines do not (hence the lovely gurgling noise on overrun).

[Retroanaconda]

Certainly does apply on a TDi. Even my ancient 6hp Lister CS will go to no fuel on overrun. The injection pump has wizardry inside it to make this happen. Carburetted engines do not (hence the lovely gurgling noise on overrun).

Do you have a source for this?

Not doubting you, I'm just interested as - like Dan above - I had assumed that the 200Tdi wasn't capable of such things and that it was a feature of more modern cars with electronically controlled injection. I figured the 200Tdi would just continue injecting "idle" fuel quantities, though obviously at a higher RPM.

How does the FIP on the 200Tdi detect that it is on over-run mechanically? It would have to be able to differentiate between the "closed" throttle position at idle and at higher RPMs (ie. over-run).

[muddy]

Just a side note about fans, I have driven to work in a tuned 300 90 with and without vicious fan, 300 disco manual with and without vicious fan, 300 auto disco with a kenlowe, mazda 35slti 90 without fan and a standard 110 hi cap td5. They all warm up to pretty much the same ( enough heater output to do something!) amount within 500 yards of one another, over different wheather, quick screen ice scrape etc.

Just something I have noted over the past year.

Will.

[TheRecklessEngineer]

Do you have a source for this?

Not doubting you, I'm just interested as - like Dan above - I had assumed that the 200Tdi wasn't capable of such things and that it was a feature of more modern cars with electronically controlled injection. I figured the 200Tdi would just continue injecting "idle" fuel quantities, though obviously at a higher RPM.

How does the FIP on the 200Tdi detect that it is on over-run mechanically? It would have to be able to differentiate between the "closed" throttle position at idle and at higher RPMs (ie. over-run).

Not really, no. It's intrinsic to the way in which a diesel works.

The only control over the speed of a diesel engine is the amount of fuel injected. So at idle, there's a governor that sticks more fuel in if the engine is below the idle speed and reduces it if it's above. This is why a diesel has so much torque at idle - the governor will increase the fueling to try and keep that idle speed.

The throttle is more of a power demand than a fueling demand and acts on another mechanism that will also vary the fuel to match the power demand of the pedal.

Finally, there's an overspeed mechanism that'll cut the fuel if the engine tops out - a limiter if you will.

So if you reduce the throttle to idle, then the idle governor will take over. Because the engine speed is greater than idle speed the fuel will be reduced to zero.

[Yostumpy]

Ok ! bit of an update. As today was nice, it did a bit of tinkering and washed the truck, then i noticed the leak off pipes were not looking too good, so replaced them with something that I had lying around, then I thought that looks the same size pipe as the boost pipe. So I nipped round the other side, and whipped off the boost pipe from the turbo, and plugged it with a screw, then pushed a small length of pipe on the turbo outlet and plugged that one too. Started it up. and it ran. So I took it for a spin. Well I have to say i was VERY surprised indeed. Folks had said it would be pants, wouldn't pull over 50mph etc etc, but I wasn't convinced by the doom and gloom merchants, ( I never am).

So what was it like then? well as I said I was surprised. As I pulled away initially i waited until the road was completely clear just in case it was really slow as predicted. BUT it wasn't, moving off isn't much different really, obviously its less powerful, but it is MUCH more powerful than a 12J n/a, prob on a par with a 19j TD. it seems happy to rev freely, seems more fun to drive, dare I say it, (round country lanes anyway). I took it out on the dual carriage way, and it pulled a desired 60mph up a long ( 1 1/2mile) incline. I decided to accelerate and although much slower, it DID pick up well. Then on the return, on the flat, I planted my foot, and (again obviously not as quick) it accelerated from 56- 75 with ease and prob would have gone over 80 with ease had I not had to turn off. So It is VERY drivable but the funny thing I noticed (as I drove with one eye in the side mirror) there was ABSOLUTELY no smoke whatsoever.

So To recap I've blanked off the turbo boost pipe, so I still have a fully functioning turbo but without the extra fuelling on boost.

The BIG question is MPG. Will it be a gain, a loss, or same as. If it is a reasonable gain (10% would be nice) then I'll plumb in some copper micro bore pipe and a small gas tap fitted in line, in the cab, so when up a long hill, or loaded I'll turn on the 'gas'. It really does go very well indeed.! Can't wait ti fill up after a couple of hundred miles ( always fill up twixt 200-250)

[landroversforever]

Will it not damage the engine running it lean when under load/boost?

[CwazyWabbit]

Will it not damage the engine running it lean when under load/boost?

Nope, diesels aren't damaged by lean running .... that is the way you control them afterall, unlike a petrol.

[landroversforever]

Nope, diesels aren't damaged by lean running .... that is the way you control them afterall, unlike a petrol.

Point me to a brick wall.... We had this convo before I'm sure! (long day!)

[CwazyWabbit]

Point me to a brick wall.... We had this convo before I'm sure! (long day!)

Lol, yep we did

Oh, there you go

[Aragorn]

Less power makes it more fun to drive?! Not sure thats possible!

The lack of smoke is expected, as your simply running much leaner at full throttle.

As far as i can see, essentially all you've done is imposed a virtual limit on max fuelling that would similarly be achieved by simply using less throttle... You've not actually made the engine any more efficient, you've just reduced the maximum amount of fuel it can possibly use (and power it can generate). It might well mean more economy ofcourse, but the same could be achieved IMO by simply using less right foot. Not sure why you think it revs any more freely, as that really shouldnt have changed. Perhaps the reduced midrange removes the "tailing off" effect you get as you climb past 2000rpm on a stock motor, which in turn makes it seem like its happier to rev?

[CwazyWabbit]

It probably would make it more efficient, isn't it hard acceleration that wastes fuel? If so the fact it won't accelerate as quickly without enforces that more economical driving style surely?

[Yostumpy]

when I say more fun to drive, what I mean is... I had the pump tweaked a while ago, and it does go very well, and when the turbo spools up it defo picks up . but in the restricted mode it was a bit like how I imagine a series motor would be with a non turbo 200tdi or maybe a perkins prima, ie adequate but not punchy, in that it is so easy to pootle around and be lazy with the gearbox, with all that power, but in an old series 2 1.4 you had limited power. i didn't mean it was more exiting ('white knuckle') to drive but sort of going back 20 years fun.

Withe regard to not using as much throttle instead, not sure I agree, as I can still rev to full revs now,but without any extra fueling, ie foot on the floor whilst accelerating with no smoke then back off when at speed. If it works mpg wise, I will fit a simple power 'tap'. I wouldn't want to tow with it like this but for most of the time it seems fine.

I didn't say it revs 'more' freely, i said 'it seems happy to rev freely', which I thought it might not with restricted fuelling.

I've not 're-invented the wheel' I'm just experimenting with something nobody seems to have to done before and nobody seems interested with.. Bet if I was to get 45 mpg peeps would listen then!

[TheRecklessEngineer]

It probably would make it more efficient, isn't it hard acceleration that wastes fuel? If so the fact it won't accelerate as quickly without enforces that more economical driving style surely?

Nope. Start reading from here: http://forums.lr4x4.com/index.php?showtopic=82309&p=707426

If you want a bit of further experimentation then fit a boost controller (£10, eBay) and set the boost to a very low pressure. It will reduce the power consumed by the turbo and should save a bit of fuel.

You could even fit it and leave the boost pipe to the injection pump connected.

I would suggest though that the fuel saved is more likely in an enforced driving style/lower average speed rather than any increased engine efficiency. But it will be interesting to see the effects.