Diesels at high and low altitudes..

[SkyPup]

As you see, TIME is 100% of the issue. The decrease in air concentration at altitude affects a diesel engine even greater than a gasoline engine, simply due to the lack of TIME for injection, vaporization, mixing, ignition, and burning which all has to occur during the top end of the injection stroke, compared to a gasoline engine having the intake stroke and compression stroke to accomplish the same thing....

 

[SkyPup]

I wonder how those formula one engines at 15,000+ RPM manage to find enough "time" while my 2,600 RPM Kubota doesn't? Thats about .002 second for complete combustion (if you assume about a 90 degree usable rotation during the combustion process). Time is not an issue.

In fact TIME is the issue -->>your 2,600rpm Kubota is never going to make it to 15,000rpms in one piece!

 

[orezok]

Interesting... this is off topic (altitude), but have you ever heard a diesel knock? Gas engines start their ignition of the fuel from a single ( or several points in the case of an F1 engine) and the flame spread is very controlled so as to not have preignition. A diesel on the other hand starts its propagation at every point within the combustion chamber at one time (relatively). The fuel literally explodes throughout the entire combustion chamber. That's what causes the knock.

And if you don't think there is enough time for complete combustion in your tracrtor engine at 2600 RPM, how do you explain how Volkswagon built a car diesel engine that runs up to 5000 RPM?

They must know something you don't!

 

[RayH]

Interesting... this is off topic (altitude), but have you ever heard a diesel knock? Gas engines start their ignition of the fuel from a single ( or several points in the case of an F1 engine) and the flame spread is very controlled so as to not have preignition. A diesel on the other hand starts its propagation at every point within the combustion chamber at one time (relatively). The fuel literally explodes throughout the entire combustion chamber. That's what causes the knock.

And if you don't think there is enough time for complete combustion in your tracrtor engine at 2600 RPM, how do you explain how Volkswagon built a car diesel engine that runs up to 5000 RPM?

They must know something you don't!

Diesel burns alot slower than gas. Its like really, really high octane gas. Knock is not a diesel issue. Diesel does more of a burn than an explosion. This is also why diesel engines run slower than gas.

 

[SkyPup]

And if you don't think there is enough time for complete combustion in your tracrtor engine at 2600 RPM, how do you explain how Volkswagon built a car diesel engine that runs up to 5000 RPM?

They must know something you don't!

Actually, you must know something we don't, as neither of our Volkswagen Turbodiesels will do over 4,800rpm for the last twelve years now!

However, on both our VW TDIs, the ECU decreases the fuel injection amount 5% for every 3,000 feet altitude above sea level and the fuel injection pump start of injection is advanced as well to account for the atomspheric differences between sealevel and elevated altitudes, even with its variable nozzle turbine and super efficient turbocompressor wheel.


If you want to use your Kubota tractor to its best advantage, take it underground into a mine somewhere a couple of thousand feet below ground, it will work much better there than at the higher altitudes you've been wondering about.....

Let me know next time you hear any diesel airplanes flying overhead too!

 

[KICK]

Every internal combustion engine, including all diesel and gasoline engines, that rely on atomspheric oxygen will lose about 5% of power for every 3,000 feet in elevation, doesn't matter if it is electronically operated or has a MAP or MAF sensor to correct for the loss of oxygen.

this is about as true a statement as you are going to read here.

something like 95% of the worlds air is below 5000 feet, so generally you wont notice a change in performance until you start getting past that point.

the difference between sea level and 5000 feet is negligible, after that it starts to show up.

someebody else mentioned electronic controls. since they are more accurate they compensate better but the engine will still lose power as the oxygen in the air becomes less dense.

 

[KICK]

Interesting... this is off topic (altitude), but have you ever heard a diesel knock? !

Yeah, when you light it off on ether.

 

[KICK]

As you see, TIME is 100% of the issue. The decrease in air concentration at altitude affects a diesel engine even greater than a gasoline engine, simply due to the lack of TIME for injection, vaporization, mixing, ignition, and burning which all has to occur during the top end of the injection stroke, compared to a gasoline engine having the intake stroke and compression stroke to accomplish the same thing....

I take issue with this.

main reason for loss of power at altitude in any diesel engine is lack of oxygen.

the time for injection and ignition are constant,ie it takes a constant amount of time for the fuel to be injected and penetrate the combustion chamber and for ignition to occur. what varies is is the amount of degres of crankshaft rotation that result while this process happens.

at low engine speeds the piston is moving slowly, the fuel injects and ignites and burns, yet in this time frame the piston would have moved less distance than if the same process happens at higher piston speeds. its one of the limiting factors in any engine.


a diesel engine isn't dependent on a standard air fuel ratio, like a gasoline engine.

engine speed and power are controlled by the amount of fuel injected.

if you have less oxygen and you add the same amount of fuel as at low altitudes, you will get more smoke and less power.
a diesel engine does not mix the fuel with the air on the intake stroke,
it doesn't vaporize the fuel upon injection-rather
it atomizes the fuel into a fine spray pattern in the cylinder.
ignition begins as soon as injection starts
generally injection begins about 30 degrees before TDC

 

[SkyPup]

No problem, but if TIME is not an issue with diesel combustion, why won't it do 15,000 rpms in an F1 engine like a previous poster prescribed?

 

[orezok]

I'm still not buying it. Dodge (Banks) set a land speed record with a Cummins at Bonneville (elevation at the track is 4,218') and this was Banks press release.

"The Banks Race Shop in Azusa prepared the Dodge Dakota pickup and included all the creature comforts for highway driving. Banks installed a compression ignition engine dyno that is able to handle up to 1000 hp, 3000 lb.ft. of torque and engine speeds of 5000 rpm."

This was a 5.9 long stroke diesel, not some wimpy Volkswagon.

Time and elevation may still be an issue, but all I hear is conjecture and "expert" opinions, but no positive facts to refute the fact that diesel engines are LESS affected by altitude change than gas engines. THAT was the basis for the original post!