Altitude Effects?

[WStayton]

Hi Guys!

  The location where I'm going to install my OM616 Mercedes 2.4 liter 4 cylinder engine is 1960 feet above mean sea level.  The engine has no form of altitude compensation that would turn the fuel down at high(er) altitudes.

  I know, from flying naturally aspirated engined airplanes, that you lose something like 3% of available power per thousand feet above sea level, so is this something that I should worry about with my naturally aspirated engine?  I was thinking that maybe the max fuel needs to be turned down a little bit so it doesn't go "over-rich" when the governor demands wide open throttle - or am I, AGAIN, making another mountain out of a mole hill?  <grin>

  It also blows my "I've got 24 kW of power available" theory full of holes, since I completely forgot to subtract the 6% that the topography has robbed me of!

  My brother's clever solution to the problem was to dig a shaft 1960 feet deep and then to install the engine/generator at the bottom of the shaft - he always was the practical one in the family! <smile>

  My going in assumption is that at sea level the engine is getting the amount of fuel that will yield maximum horsepower - but I'm not sure how good of an assumption that is, since Mercedes may have resticted the fuel to insure long engine life - though with only 72 HP available, per the engine's rating, I don't think that they had room to give much away to make ANYBODY happy!

  I was wondering if operating the engine in this "over-rich" (by 6%) environment would suppress available horsepower by more than just the 6% that I am losing due to altitude?

    There is, BTW, a well documented "screw" under the front/back cover (depending on which way you look at it) that is to adjust the total max fuel delivery, so the condition is easily adjusted if I want to get in it and mess around.

  So what do you think, guys - should I turn the fuel down slightly so that it doesn't go over rich, or should I keep my mitts off of the innards of the injection puimp or should I wait and operate it and see how black the smoke is when the governor demands wide open throttle?

  Opinions solicited!

Regardz,

Wayne Stayton

[Tom Reed]

I say run it and if it belches black smoke at full load turn down the smoke screw. The other solution is to add a turbo. 

[bschwartz]

I'm at 4800 ft, and my 1980 mercedes 240 NA engine never let out black smoke.  Just run it.

[mobile_bob]

diesel engines by their very nature are lean burn engine's generally always running with an excess of oxygen
while you will lose about 3% per thousand feet, the engine will only run rich with black smoke when it has enough load on it
to do so.
a typical 6hp listeroid that starts to make black smoke at sea level with a 6hp load, probably would do the same smoke at about
5.5hp load at your elevation.  up to that point the engine would run just like it would at sea level, in other words with any load under
about 5.5 hp the exhaust would be the same at your elevation as it would at sea level.

bob g

[BioHazard]

If you find that you don't have enough horsepower, maybe you might want to think about a little bit of propane injection. Supposedly like nitrous for a diesel, and currently cheaper than diesel fuel....

[TimSR2]

It's not a gas pot!  There is no  need to recalibrate fuel equipment for altitude.  The governor will always attempt to provide enough fuel to attain the required RPM no matter the air pressure.   Old school diesels almost always run in excess air combustion  so altitude compensation is not an issue.

[WStayton]

Hi Guys!

  I was under the impression that conventional diesels ran at a fueling rate where about 80% of the availble oxygen was used for combustion AT SEA LEVEL.  The excess of air was/is to have orderly conbustion and not a lot of black-smoke/soot.  I recall an elderly Mack that my cousin had, which started out life as naturally asperated and on which he 1) Added a turbocharger and 2) Turned the injection rate up to take advantage of the increased air that the turbo gave him.  He had to drive this beast with a real "feather-foot" when in town because the fuel injection system would respond, immediately, to the demand via throttle, for more fuel and the turbo would take a while to spool-up and supply the increased air. The cloud of black smoke caused vastly increased interest from law enforcement types.  Anyhow, my concern was that I would eat in to the extra air supplied to insure proper combusiton and reduce smoke/soot.

bschwartz:

  Do you have any idea if this is typical of all or most 240D's?  Maybe yours was/is just set a little leaner to begin with - I would expect that by the time you got to 4800 feet the extra air would have been used up, no?  Your 240D engine is almost exactly the engine that I am planning to use, so whatever happened to/with it, I would also expect to happen to mine!  (Your 1980 was 2399 cc and my marine enigine is 2404 cc, with the same new-design head/combustion-chamber the 1980 240D has.)

mobile_bob:

  I realize that the "overfueling" is only a potential problem when the governor puts its foot to the floor - which, I guess, whouldn't be much of the time - or I have a BIG design problem!  <grin>

BioHazard:

  I had thought, briefly, about propane injection, but I never got beyond the "thought" process.  My guess is that I will be running at least 50% power any time I have the generator on so I guess I could set it up to use 40%-45% propane and then let the governor make up anything else it needs/wants with the diesel-fuel/veggie mix that I plan on using.  I THINK I read somewhere that using a partial fueling of propane cuts down on the deposits, so that is atractive from a standpoint of using diesel/WVO mix, but I'm not convinced that it will clean up all of the "junk" that comes in the WVO and gets burned - but it has to help, since it automatically gives you a smaller precentage of total fueling that is WVO.  However, even though propane is cheaper, per BTU, than pump diesel, I don't think it is cheaper than WVo, which is almost free!  <grin>  Maybe I could use a liquid fuel mixture that had a larger percentage of WVO in it, though, and save some money that way.  But, I don't think that the propane lets me get more total horsepower out of the engine, since there has to be air to burn the fuel, and if I'm also short of air due to altitude, it isn't going to help that problem.

TimSR2:

  I agree that the fuel control will add more fuel, up to its set-point, to try and maintain rpm, but that fuel only does the engine any good if there is any excess air there to burn the fuel.  In fact, if it runs too rich the quality of the combustion degrades and the engine actually produces less horsepower when you add more fuel, not more - I've seen this demonstrated with a ford 6.9 liter IDI v-8 on a dyno.  As they increased the fuel, above the normal max, they got more HP, for a while, and then as they added more fuel, the power dropped off - So its not the old "if some is good, more is universally better" story.  I think in the tests that I saw them doing, the limit for more power was about 10% more fuel than stock fuel delivery - after that you got less power, not more.


  Tom:

  About the turbo;  Mercedes sold 2.4 liter 4 cylinder units with a turbo in Europ, but NONE of them have gotten the coveted Mercedes 500,000 km badge!  Also, none of the five cylinder turboed version of essentially the same engine have gotten a 500,000 badge.  Meanwhile, in the general population of naturally asperated 4/5 cylinder engine, something like 2% of them have made it to 500,000 and beyond - with record being an engine that made 1,000,000 km without having the head off!!!

  From all of this, I conclude:  Turbo does not equal longevity!  So, thanks, but no thanks!  <grin>


  Okay, you guys have convinced me that I should at least try it the way that it is, before I think about turning the fuel down!  I will have enough things going on that it will take me a while to figure out who is doing what, with which and to whom  anyways!  <grin>


  Thanks for the input guys - I sorta figured I should at least try it first, but it a lot easier to have faith in your convictions when everybody is standing there saying "Yea, do it!"!

Regardz,

Wayne Stayton