Diesels at high and low altitudes..

[cp1969]

I've been pondering this and though I'm no expert, there seems that there would be a difference between gas and diesel engines. All engines lose power at altitude, but I think diesels would lose less. Gas engines have to run a a very narrow fuel to air ratio (about 15:1). Diesels, because they run unrestricted have a very wide ratio from 100:1 at idle to ??:1 at full power. Given this information, it would seem that the diesel would maintain it's full power up to a higher altitude when the amount of air falls below it minimum F/A ratio.

Hmmm...

I think you are right.

Yep. I have less power (about 6-8% at 8500 ft MSL) than you folks down by the big ponds, but I use less fuel/hr at a given RPM than you do, since fuel is mixed as a ratio to O2!!!

Are you talking about a diesel? If so, that is not the way a diesel works.

Fuel makes power...the engine is just a mechanical contraption to accomplish the conversion of chemical energy in the fuel to mechanical energy. On a gas engine, the amount of fuel going into the engine diminishes as altitude increases because there is less O2 for the fuel to combine with and the fuel/air ratio is limited to a very narrow range, compared to a diesel. The diesel starts out with a surplus of air and the amount of fuel going into the engine is not reduced...so why would the power be reduced?

 

[orezok]

At some altitude, the amount of oxygen available would be less that the amount needed to combust the fixed fuel amount efficiently (that is the mixture would be overly rich). What ever that altitude is, the power would have to start dropping off.

One can see from the smoke generated by pulling tractors that that F/A ratio can get quite high before the maximum F/A ratio and power is reached.

Conclusion (by me anyway) is that if the tractor isn't pouring out black smoke, it's probably still producing close to maximum power.

 

[SkyPup]

Nope, no difference between a gasoline and a diesel engine, they both lose the same amount of power because they both lose the same amount of oxygen.

 

[Doc_Bob]

Nope, no difference between a gasoline and a diesel engine, they both lose the same amount of power because they both lose the same amount of oxygen.

That is the beauty of a turbo, altitude has less of an impact (almost none) 6 PSI at 10000 feet same as 6PSI at sea level.
Bob

 

[cp1969]

Nope, no difference between a gasoline and a diesel engine, they both lose the same amount of power because they both lose the same amount of oxygen.

But...there was an excess of oxygen to start with. How does losing what was not being used cause a loss of power? Remember, fuel makes power...the amount of fuel going in didn't change...what happened to the energy from the fuel if the engine is producing less power?

 

[RayH]

I know I will get disagreement on this but here it is anyway.
There is not less oxygen at high altitudes. The percent of oxygen in the air is the same. The problem is the reduced atmospheric pressure at altitude. Lower pressure means less air available for the engine to use to burn its mixture. This is the reason why turbos and superchargers work well on high altitude applications. Think about it, turbos dont change the percent of oxygen, all they do is increase the air pressure.
Modern EFI engines will adjust the fuel to match the density of the air at altitude, less air = less fuel. This also means less power is produced.

 

[orezok]

At altitude the oxygen molecules are spread further apart, so are the nitrogen and 1% of other gasses. What I was saying that per cubic inch of "air" aspirated into the engine there are less oxygen molecules. There are still excess oxygen molecules in respect to fuel molecules until the altitude at which the perfect F/A ratio is reached, hence less loss of power to some given altitude.

Back up your statements with some basis in fact.

 

[SkyPup]

At altitude the oxygen molecules are spread further apart, so are the nitrogen and 1% of other gasses. What I was saying that per cubic inch of "air" aspirated into the engine there are less oxygen molecules. There are still excess oxygen molecules in respect to fuel molecules until the altitude at which the perfect F/A ratio is reached, hence less loss of power to some given altitude.

Back up your statements with some basis in fact.

Your theory is interesting....

But here are the facts -> no difference between a gasoline and a diesel engine, they both lose the same amount of power because they both lose the same amount of oxygen.

LOL, talking about a diesel being "Able" to run anywhere between a 15:1 and 100:1 ratio compared to the correct stoimetric 14.7:1 for a gasoline engine doesn't mean anything.

You think a diesel engine has any power at 100:1? No, it is idling.

Total different story under load.

 

[bx23barry]

But...there was an excess of oxygen to start with. How does losing what was not being used cause a loss of power? Remember, fuel makes power...the amount of fuel going in didn't change...what happened to the energy from the fuel if the engine is producing less power?

There is (hopefully) only an excess of oxygen at less than full power. At full power an engine (gas or diesel) will/should be burning all the available air/oxygen (more fuel cannot burn with out oxygen=black smoke). So power is limited by the available air/oxygen (and fuel). The higher the altitude the, the less air pressure, the less air density, the less available air/oxygen. So there is less power available at higher altitudes. Even a tubocharged/supercharged engine will make less power at altitude. Noone sets ¼ mile records in Denver but lots of records at Pomona.

 

[SkyPup]

But...there was an excess of oxygen to start with. How does losing what was not being used cause a loss of power? Remember, fuel makes power...the amount of fuel going in didn't change...what happened to the energy from the fuel if the engine is producing less power?

Less atomspheric pressure is a 100% direct correlation to less power in naturally aspirated diesel engines, gasoline engines, propane engines, vacuum pumps, compressors, water temp boiling, O2 to hemolglobin binding, or any other oxidative process, etc. etc. etc.

You could try to advance your high altitude diesel fuel injection pump timing a couple of degrees to try to give the fuel more time to mix and burn so it wouldn't be running so rich and creating both horsepower and torque loss, but even then you'd still be losing power......