Diesel Engine Performance at Altitude

Submitted: Wednesday, Nov 12, 2014 at 09:55
ThreadID: 110117 Views:2452 Replies:8 FollowUps:13
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Hi all, was towing my 1,600kg camper with our BT50 (2011 model) over Mt Hotham the other week when I noticed a considerable decrease in power on the steeper climbs as I neared the top of the mountain which I've never noticed when travelling this road without the camper.
I'm assuming that this was because at altitudes approaching 2,000m there's less oxygen available so the engine works less efficiently but I'd appreciate some feedback from people who may know a bit more about this sort of thing than me.
Regards, Gary M.
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Reply By: Athol W1 - Wednesday, Nov 12, 2014 at 10:07

Wednesday, Nov 12, 2014 at 10:07
Gary
There are 3 possible causes for this, firstly it is the effect of altitude with thinner air and a lower pressures effectively giving less oxygen in the engine to burn the fuel as you are aware, and secondly a fuel filter that is nearing the end of its life as it can restrict the fuel flow, which becomes more noticeable the longer that the engine is required to give full power (nearing the top of a long climb). The third being an air filter that is nearing the end of its life and causing a restriction that is adding to the lack of oxygen in the high altitude air.

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Follow Up By: Member - Gary R M (VIC) - Wednesday, Nov 12, 2014 at 16:39

Wednesday, Nov 12, 2014 at 16:39
Thanks Athol, only recently had a 100,000km service so hopefully filters are ok but much appreciate your advice.
Regards, Gary M.
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Reply By: HKB Electronics - Wednesday, Nov 12, 2014 at 10:30

Wednesday, Nov 12, 2014 at 10:30
Yes as you climb higher the air pressure decreases and power with fall off, around 3% per 1000 feet of elevation.

Another item you could check is MAF sensor, if your car has a hot wire type and it is dirty it could possibly be not giving correct mixtures to the motor, same applies to the MAP sensor if fitted.

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Follow Up By: HKB Electronics - Wednesday, Nov 12, 2014 at 10:34

Wednesday, Nov 12, 2014 at 10:34
Is your BT50 turbo charged, if so then the ECU may be able to compensate somewhat for altitude by increasing boost pressures but not sure about that one?

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Follow Up By: HKB Electronics - Wednesday, Nov 12, 2014 at 10:39

Wednesday, Nov 12, 2014 at 10:39
And don't forget 1600KG camper, is like carting 16 extra passengers around!

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Follow Up By: Member - Gary R M (VIC) - Wednesday, Nov 12, 2014 at 16:42

Wednesday, Nov 12, 2014 at 16:42
Thanks HKB, yeah at nearly 6,000 feet up I'd reckon power was down something like 3%x6=18%, at least that's what it felt like compared to a steeper section near the bottom of the mountain where I didn't have any concerns.
Cheers, Gary M.
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Reply By: Bob Y. - Qld - Wednesday, Nov 12, 2014 at 10:33

Wednesday, Nov 12, 2014 at 10:33
Gary,

May well be an accumulation of 3 things, altitude, fuel filter and most of all, the 1600 kg camper.

Once you start dragging something behind the vehicle, it will have a marked effect on performance, on steep climbs.

Severely restricted air filter should produce an excess of black smoke when under load.

Bob

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Reply By: Ron N - Wednesday, Nov 12, 2014 at 11:22

Wednesday, Nov 12, 2014 at 11:22
Gary - You shouldn't notice any appreciable difference in power from a diesel until you reach 3000M or more.
If you're running a turbocharged diesel (and I note both BT-50 diesel engines are turbocharged), then the loss of performance is even less than a naturally aspirated diesel.

As a diesel starts to work harder with climbing, so the combustion temperature/exhaust gas temperature (EGT) starts to climb.
Turbocharger performance is affected by EGT. As the EGT rises, the exhaust gases expand substantially and the turbocharger spins faster - thus compressing the incoming air a lot more, and providing more oxygen to the engine.

A diesel at high altitude is affected far less than a petrol engine, because a petrol engine is very dependent on the critical fuel-air ratio.

If you operate over 3000M, diesel fuel injection pumps usually need to be adjusted a little to compensate for the thinner air.

The three greatest single features affecting diesel performance are the incoming air temperature - the incoming air supply availability - and the prompt availability of fuel when power is required.

As you increase in altitude, the air temperature drops rapidly. Incoming air that is cold, is more dense than hot air, and therefore contains more oxygen - so this helps offset the increase in altitude.

A partially-blocked fuel filter will have a far greater effect on diesel performance, than any increase in altitude.
A partially-blocked air filter will have the next biggest effect on performance.

So on that basis, check or replace your fuel filter first, the air filter second, and then check for correct operation of the turbocharger.

Cheers, Ron.
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Reply By: Member - Bruce C (NSW) - Wednesday, Nov 12, 2014 at 11:50

Wednesday, Nov 12, 2014 at 11:50
Hi Gary,
I have experienced this also with both turbo diesel and petrol cruisers I have had when towing our 2+ tonne caravans topping the Great Dividing Range on the Oxley Highway east of Bendermere. It is more noticable when you are confronted with sharp inclines with bends at the bottom. Once momentum is lost under such circumstances it is more difficult to get it back the higher you get.

Many of the local younger fellows go motorbike riding up the Oxley highway climbing from Wauchope up to Yarrowitch Valley on top of the table land and they complain that they can do a lot less with their bikes up there than they can down nearer sea level.

I have noticed that when I have been driving on the range for some hours, once I hit the Pacific Highway it is as good as increasing the boost on a turbo. even the petrol seems like it has gotten an extra couple of cylinders. But it is only noticable when towing the larger loads such as you suggest.

Cheers, Bruce.
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Reply By: The Bantam - Thursday, Nov 13, 2014 at 19:24

Thursday, Nov 13, 2014 at 19:24
While modern engines both petrol and diesel can correct for any air fuel mixture problems......it is a known fact that ALL internal compustion engines suffer at altitude.

Internal combustion engines function on compression.....if there is less natural air pressure there will be less air charged into the combustion chamber therefor less power....regardless of engine type

This can appear more dramatic that some may expect.

It is such a problem that in some very high altitude railways they still use steam.....because steam is far far less disadvantaged by altitude.

then there is the idea that while a modern fuel injected motor...diesel or petrol...may correct mixtures fine..and be quite happy at average power outputs.....the engine management may reduce power further at altitude for a variety of reasons.

Altitude will effect compression, mixture and a whole pile of other things....so the ecu might not like the resultant EGTs, emissions or just get confused.

If it is a reasonably new and in good condition vehicle that powers and drives well otherwise....there is probably not a damn thing wrong with it.

Yes ALL internal combustion engines are effected by altitude...and maybe more than you expect.

cheers
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Reply By: Member Kerry W (WA) - Friday, Nov 14, 2014 at 00:46

Friday, Nov 14, 2014 at 00:46
Hi Gary,

I trust some of this is relevant for you.

I lived for several years at 3000"' (at Armidale in NSW) and often drove considerable distances up to elevations of 5500' in petrol vehicles in the 1970s and 80s (So 1000m to around 1800m in elevation).
Yes altitude and lower air density is a drag.
We were very much performance orientated in those days and often fiddled with carby fuel/air mixture (because we could back then) to compensate when we were heading up into the really high country.
Eventually, I had a pretty good idea how performance would suffer going from sea level to 1800m. I also worked out how to get the most out of the engines as well. Making them run a bit leaner was all we could realistically do.

Since around 2000 I have travelled the same roads with a friend who drove a modified 4.2 lit Turbo GU Patrol while I drove a reasonably high performance (modified non turbo) 3 Lit Petrol GQ Patrol (with the old high revving but traditionally underpowered Skyline RB30S donk).

The long and short of it was the 4.2 Turbo Patrol did not suffer much at all from the altitude. (It did however have a larger turbo than factory) Whereas my usually gutsy 3 lit petrol went from leaving the Turbo diesel in its dust at sea level to having trouble even keeping at speeds over 90kph up at altitudes over 1400m and certainly suffering at 1800m.

I can affirm the fact that the Turbo Diesel coped far better at altitude than the naturally aspirated petrol engine. I would assume that a naturally aspirated diesel would notice a considerable effect with the lower oxygen levels at altitude.

After my experiences in the 70s and 80s i tried a few experiments with the old Patrol and eventually had some success in the late 2000s
I improved the performance of my Petrol at high altitude by attaching a 60 square inch air dam to the snorkel. It seemed to keep the vehicle from running too rich. At speeds of around 110kph I was at least keeping up (or seeming to keep up) with the Turbo Diesel on those high altitude runs. So there seems to be a degree of forced air induction working at those higher speeds.

Obviously the whole reason vehicles are turbo charged is to increase the density of the air and hence O2 flowing into the engine.
It is a known fact that high air temperature even at sea level reduces the density of the air and the amount of available oxygen for any internal combustion engine hence the use of intercoolers and forced air induction and snorkels (to scoop in cooler air from away from the engine bay and warmer road surface) to keep air temperature flowing into the engines cool as possible to improve efficiency and combustion via slightly denser air and hence higher Oxygen levels..

Similarly the effects of altitude can be slightly compensated for by the extra density of air at cooler temperatures.

I can attest to the higher density of cold air and how easy it is to stuff up modern vehicle modifications.
Recently a good friend fried the bores on his cylinders on a very cold night near sea level after he turbo'd his near new diesel engine and had too much fuel flowing into the engine. Obviously in hindsight his fuel levels were above factory settings and the dense cold air (carrying more oxygen which ran the mix hotter than ever) was the straw that broke the camels back so to speak.

His son was driving (no doubt hoofing it) - towing a heavy trailer up a steep long hill in southern WA in winter - ignoring the pyro gauge which undoubted would have indicated too high a combustion temperature - caused by a combination of denser air (more O2) and plenty of fuel. Needless to say as the bores overheated and became scored - the thing lost compression on the hill simply conked out - and would not start again! No Compression! The vehicle had performed the same tasks in warmer air temperatures without a problem.
When we pulled the head off - it had scored the tripe out of the cylinders - an expensive lesson.

Hope this feedback is useful, again I can only speak from personal experience and a reasonable understanding of the physics involved.
Kerry W (Qld)
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Reply By: Member - Boobook - Friday, Nov 14, 2014 at 12:12

Friday, Nov 14, 2014 at 12:12
It has got almost nothing to do with altitude, blocked filters etc etc. You can experience similar loss of power at 600m or 200m.

The loss of power is almost totally due to the intercooler heating up as you climb the hill with that load. If the intake air goes from about 20 degrees to about 100 degrees as the intercooler heats up that is about a 25% loss in power due to the lower air density.

If you stopped for 30 mins or so ( after letting the engine idle for a few minutes) then you would get full power back till it gets hot again.

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Follow Up By: Shaker - Friday, Nov 14, 2014 at 12:19

Friday, Nov 14, 2014 at 12:19
That's one of the drawbacks of top mounted intercoolers!

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Follow Up By: Member - Frank P (NSW) - Friday, Nov 14, 2014 at 16:08

Friday, Nov 14, 2014 at 16:08
You'll likely be going slow so there won't be much airflow.

I've read about thermo-fans being installed to help out with cooling the intercooler. I wonder if it's worthwhile.
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Follow Up By: The Bantam - Friday, Nov 14, 2014 at 16:24

Friday, Nov 14, 2014 at 16:24
AHH nowe here is another thing.

less dense air cools less efficiently.

cheers
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Follow Up By: Member - Boobook - Friday, Nov 14, 2014 at 21:37

Friday, Nov 14, 2014 at 21:37
Ahhh now here is another another thing.

Atmospheric temperature drops by about 5 degrees per 1000m of altitude. Making engines more efficient.



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Follow Up By: The Bantam - Friday, Nov 14, 2014 at 22:17

Friday, Nov 14, 2014 at 22:17
Ahh yes but as you move inland the daytime temperatures increase.....and most of our mountain ranges are inland.


Its all very complicated
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Follow Up By: Dave(NSW) - Friday, Nov 14, 2014 at 23:13

Friday, Nov 14, 2014 at 23:13
.....and most of our mountain ranges are inland.

I thought the Great Divide was close to the coast.
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Follow Up By: Member - Frank P (NSW) - Friday, Nov 14, 2014 at 23:28

Friday, Nov 14, 2014 at 23:28
Pilots have been dealing with this ever since Pontius got his wings :-)

They use a pretty much standardised circular slide rule that among many other things enables them to calculate density altitude so they can work out take-off performance which among other things depends on engine power.

Set known elevation on a scale and against temperature read off density altitude in a "standard atmosphere". This is then used in a performance graph specific to the aircraft to determine if it will get off the ground in the length of runway available.

Pic below. There are aviation type electronic pocket calculators that do the same thing now.


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Follow Up By: The Bantam - Saturday, Nov 15, 2014 at 00:21

Saturday, Nov 15, 2014 at 00:21
quote
I thought the Great Divide was close to the coast.

well that depends on where you are and what you call close

Where I live the range is a bit over 100Km from the coast

& out there its either 5 degrees hotter or 5 degrees colder than it is here on the coast...which ever isn't your preference at the time.

cheers
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Follow Up By: Member - Boobook - Saturday, Nov 15, 2014 at 05:35

Saturday, Nov 15, 2014 at 05:35
It doesn't matter where any mountain is. If it's 1000m high it will be 5 degrees cooler at the top then at the bottom. If you drive up it and have power loss the mountain doesn't move to the coast.
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