High Altitude???

[jetenginedoctor]

Already proved it, but thanks anyway.

Buddy, you haven't proven anything. If you've got something to say, lets hear it?

 

[CJEliassen]

Buddy, you haven't proved anything. If you've got something to say, lets hear it?

Ok, here it is. Go back and read my posts. If you can explain why a Seneca II has a higher horsepower rating at 12,000 feet then at sea level, then you might be on your way to understand why you are wrong.



And I am not your buddy.

 

[jetenginedoctor]

Ok, here it is. Go back and read my posts. If you can explain why a Seneca II has a higher horsepower rating at 12,000 feet then at sea level, then you might be on your way to understand why you are wrong.



And I am not your buddy.

Those ratings at elevation are nothing more than an engineer's calculation. Do you think that they ran that engine on a dyno at 12,000 feet? On one hand, you've got people in this forum who are talking about a turbocharged diesel pickup engine and the effects that radical changes in altitude have on it. On the other hand, you're in here using a completely unrelated example that is, by the way, less verifiable than what I'M telling here. The Seneca is using the turbo to extend it's performance envalope at higher elevations. That we can probably agree on. The issue that we cannot seem to agree on, is that turbocharged engines are not immune to decreasing inlet density. Maybe the Seneca II does make more power at 12k feet than it does at SL. Does it make even more at 15k feet? It'd have to in order to make your argument valid. By your logic, increased altitude makes turbocharged engines work better. I think you and I both know better than that, but are you going to admit to it?



So how bout it, does that Seneca make more power at 15k than 12k?????

 

[CJEliassen]

Obviously you haven't been reading all my posts, and you don't have the knowledge to understand the basic principles. I suggest you go back to school.

 

[jetenginedoctor]

Obviously you haven't been reading all my posts, and you don't have the knowledge to understand the basic principles. I suggest you go back to school.

Wow. Is that the best you've got? I'm really disapointed. FYI, I've got the degree and the licenses, thank you very much. I've read your posts, and it all boils down to you using some half-baked theory about reduced backpressure (uh-huh) causing turbocharged engines to make more power with increased elevation. BULL! As I said, if that were the case, your example engine would make even more power at 15k feet than it does at 12k feet. Until you can explain that fact away, it would appear that you're the one who needs to go back to school and learn the basics. I don't care if you think my attitude is bad (thanks for the PM, coward. ) I'm right and I can prove it.



Have dyno, will travel.

 

[CJEliassen]

Bholm, You had the right idea. You just can't have an intelligent mature conversation with some people. I shouldn't have gotten into an arguement with someone who has a degree and the rating even though I have 10 times the ratings and higher ratings at that, a BS degree in aviation, own my own maintenance shop, work on piston and jet engines, write the training materials that he probably used to get his rating, and actually fly and teach in the aircraft he knows so much about. I guess being a student pilot since 1996 and an aircraft mechanic who doesn't even work in the industry makes one more knowledgable than someone who has taught since 1993 and worked as a mechanic since 1995. Who would've thought.



Jetboy, if I thought you have any ability to learn something new, then I would be glad to explain it to you. But you simply have a bad attitude and have limited yourself because you think you know everything already. I am glad you don't work in aviation because you would likely be getting people killed with that attitude. Hopefully you will someday mellow out and open your mind to learning once again. But until then, having a mature intelligent conversation with you is pointless.

 

[BHolm]

CJ, It is easy to get sucked in... I did it too. The funny part is that the original intent of the post was to determine if a CTD lost significant performance at altitude. I say it doesn't, you say it doesn't, heck even Cummins themselves say that there is no loss up to 10,000ft.



I certainly do not claim to have the background either of you guys have with regards to aviation. I do have considerable real world experience with the effects of altitude on gas and diesel engines in vehicles, forced induction and N/A. It is pretty obvious to anybody who lives in the real world that forced induction, depending on the specific application, can compensate or eliminate losses due to altitude.



Going around and around with Jetboy is in fact pointless. From his posts it is clear that if there was even a 1hp loss that he would feel vindicated and "right", even though a result like that actually proves "us" right.



Attitude is a big deal. TDR is a great place because most have a good attitude. I WOULD meet with most members here. Jetboy... no way, who wants to deal with a nut like that?

 

[CJEliassen]

Bholm,



Here, here.



Where abouts in Colorado do you live? I am in Shawnee which is on 285 between Denver and Fairplay.

 

[Vaughn MacKenzie]

Funny read you guys. . . doesn't take much to turn Jetdoc's crank huh? :-laf LOL



My two cent's worth is:



At 10,000 feet you have 70-75% less air than at sea level, so at best a naturally aspirated engine will have about 70% of its sea level power. It will be less though because because the relative friction and pumping effort becomes much greater in ratio to available air and thus take even more away from power making it to the rear wheels.



On turbo engines assuming we are operating below the level the wastegate opens the power levels can be figured in proportion to boost pressure plus ambient pressure. Sea level = approx 14. 5psi, 10k feet = approx 10psi. At 30lbs boost for example at sea level, you are effectively moving the amount of air 30+14. 5psi = 44. 5 final, at 10k feet you are moving 30+10psi = 40. 0 final. That comes out to 10% less air moving through the motor at 10k feet, which matches the statement I saw by Cummins saying you lose 1% power per 1000 feet. As with NA engines pumping losses and friction become greater in ratio to available power but won't be as great of an effect.



So to summarize both NA and turbo engines lose power as you gain elevation, but turbo engines lose less. Put simply a general rule of thumb. . .



3% power loss per 1000ft for NA engines

1% power loss per 1000ft for turbo engines



Vaughn

 

[jetenginedoctor]

Bholm, You had the right idea. You just can't have an intelligent mature conversation with some people. I shouldn't have gotten into an arguement with someone who has a degree and the rating even though I have 10 times the ratings and higher ratings at that, a BS degree in aviation, own my own maintenance shop, work on piston and jet engines, write the training materials that he probably used to get his rating, and actually fly and teach in the aircraft he knows so much about. I guess being a student pilot since 1996 and an aircraft mechanic who doesn't even work in the industry makes one more knowledgable than someone who has taught since 1993 and worked as a mechanic since 1995. Who would've thought.



Jetboy, if I thought you have any ability to learn something new, then I would be glad to explain it to you. But you simply have a bad attitude and have limited yourself because you think you know everything already. I am glad you don't work in aviation because you would likely be getting people killed with that attitude. Hopefully you will someday mellow out and open your mind to learning once again. But until then, having a mature intelligent conversation with you is pointless.

You only know a little about me, buddy. Based on your dates, I was an aircraft mechanic before you were. I never wasted any time working for peanuts (General Aviation) instead went to corporate aviation. The market decline put that in jeapordy and OBL and the 911 posse' found me moving into the power generation industry. I made one hell of a lot more money operating big turbines than you'll ever scratch up doing 100hr's and annuals. Now, my career path has put me in a head-on collision path with guys like you who make claims, but aren't ready to back them up. If you think you're so GD smart, take me up on my bet! If you know so much about me, you know what part of the country I'm from, and know damn good and well I mean business when I say I'll put my money where my mouth is.



Anyway, CJ, you're just a punk. If you were so sure of yourself, you'd be a bit more willing to prove it.

 

[CJEliassen]

Funny read you guys. . . doesn't take much to turn Jetdoc's crank huh? :-laf LOL



My two cent's worth is:



At 10,000 feet you have 70-75% less air than at sea level, so at best a naturally aspirated engine will have about 70% of its sea level power. It will be less though because because the relative friction and pumping effort becomes much greater in ratio to available air and thus take even more away from power making it to the rear wheels.



On turbo engines assuming we are operating below the level the wastegate opens the power levels can be figured in proportion to boost pressure plus ambient pressure. Sea level = approx 14. 5psi, 10k feet = approx 10psi. At 30lbs boost for example at sea level, you are effectively moving the amount of air 30+14. 5psi = 44. 5 final, at 10k feet you are moving 30+10psi = 40. 0 final. That comes out to 10% less air moving through the motor at 10k feet, which matches the statement I saw by Cummins saying you lose 1% power per 1000 feet. As with NA engines pumping losses and friction become greater in ratio to available power but won't be as great of an effect.



So to summarize both NA and turbo engines lose power as you gain elevation, but turbo engines lose less. Put simply a general rule of thumb. . .



3% power loss per 1000ft for NA engines

1% power loss per 1000ft for turbo engines



Vaughn

Vaughn,



There is roughly 68. 5% the air pressure at 10,000 feet versus sea level. 29. 92 inches of mercury is standard pressure at sea level, and 20. 5. Now, a naturally aspriated engine will produce more than 68. 5% of its sea level power. It will actually produce around 70. 5% of its rated power. Why is this? At sea level, lets says you close the throttle plate on a gas engine so that you have a manifold pressure of 20. 5 inches. At 10,000 feet, you need a fully opened throttle plate. (You won't get quite 20. 5 inches, but close. ) Now, you have a greater volumetric efficiency, and you also have a whole 9. 4 inches less backpressure out the exhaust. You will produce more power at 10,000 feet for the same manifold pressure as you do at sea level. Total horsepower is lost, but horsepower for a given manifold pressure increases.



Now, on our turbocharged diesel engines. The wastegate works off of absolute pressure, not gauge pressure. If we worked off gauge pressure, then we might as well have a gear driven supercharger on the engine and not a turbocharger. As you climb in altitude, you will see your max boost climb. So, again you have the same manifold pressure, but less exhaust back pressure. Volumetric efficiency is still the same because we have no throttle plate. Where you will lose power is when the wastegate is fully closed and you are still climbing, or you hit max EGT's and you start defueling.

 

[Vaughn MacKenzie]

Interesting point on the manifold pressure, makes sense I guess CJ. So does the backpressure thing. On the flip side the turbocharger has to work harder to compress air to make the same amount of indicated boost because there is less air to grab.



The EGTs rise because there is less air mass going through the engine at X lbs of indicated boost compared to sea level.



There are many variables to this topic and I think each of us understands these variables to different degrees and part of the disagreements and misunderstandings are because of this. I realize there is a lot I don't fully comprehend on the subject. Makes for interesting discussion that's for sure.



Vaughn

 

[CJEliassen]

Vaughn,



Yes, the turbo has to squeeze the air more and it does get hotter. However, the total increase in temp from the difference in pressure at sea level versus 10,000 feet is around 92F. Now, you have air going through the intercooler that is 10 degrees cooler at 10,000 feet. The intercooler will cool the intake charge more efficiently when there is a greater temperature differential. I couldn't venture to guess the total change in temperature of the intake air after going through the intercooler, but it is something less than 92F.



Now, the Egt's go up slighty from this increase in intake air temp, but they also increase because the wastegate is closing forcing more air through the turbine. This creates a restriction and causes EGT's to increase. In reality the gases are not allowed to expand as quicky and cool off, but we see that in higher EGT's versus at lower altitudes

 

[rbattelle]

Vaughn,



There is roughly 68. 5% the air pressure at 10,000 feet versus sea level. 29. 92 inches of mercury is standard pressure at sea level, and 20. 5. Now, a naturally aspriated engine will produce more than 68. 5% of its sea level power. It will actually produce around 70. 5% of its rated power. Why is this? At sea level, lets says you close the throttle plate on a gas engine so that you have a manifold pressure of 20. 5 inches. At 10,000 feet, you need a fully opened throttle plate. (You won't get quite 20. 5 inches, but close. ) Now, you have a greater volumetric efficiency, and you also have a whole 9. 4 inches less backpressure out the exhaust. You will produce more power at 10,000 feet for the same manifold pressure as you do at sea level. Total horsepower is lost, but horsepower for a given manifold pressure increases.



Now, on our turbocharged diesel engines. The wastegate works off of absolute pressure, not gauge pressure. If we worked off gauge pressure, then we might as well have a gear driven supercharger on the engine and not a turbocharger. As you climb in altitude, you will see your max boost climb. So, again you have the same manifold pressure, but less exhaust back pressure. Volumetric efficiency is still the same because we have no throttle plate. Where you will lose power is when the wastegate is fully closed and you are still climbing, or you hit max EGT's and you start defueling.

Good post.



-Ryan