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#21
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On Tue, 04 Oct 2005 15:44:16 +0000, Mike Rapoport wrote:
The heating of the intake and the consequent reduction in density is the reason that I think it will take more MP to produce the same HP at higher altitudes with a turbocharged engine. At the same MP/RPM a tubocharged engine is effectively running at a higher density altitude than a normally aspirated one. The turbocharged engine is also running at a higher density altitude as altitude increases at the same PM becasue there is more compression required, therefore more heating. The intake air is heated *substantially* and its density is reduced substantially. Natually, the effect is strongest at high manifold pressures and high altitudes. I agree that reduced pressure at the exhaust helps and an intercooler certainly helps too. Just tossing this out there... The final rise in temp is always relative to the ambient air temp. At altitude, where temps can be quiet cool, you are getting a modest "intercooler" effect. Additionally, amount of boost provided by the turbo dramatically effects the temp delta. As an example, a turbo pushing 10 psi, with no intercooler, may cause a temp delta of 100' F (real world number), measured at the intake. If you are at altitude, where ambient is quiet cold, say, 40-50' F., then the intake temp, given the same boost, may only be 140-150'. Compare this to take off, at sealevel, on a 95' F day, the intake charge may measure ~200' F, given the same boost. Turbonormalized is a little bit different because the boost is going to be much lower at take off than at altitude...nonetheless, you are still getting an intercooler-like effect from the cooler ambient air. Greg |
#22
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Greg Copeland wrote:
: Just tossing this out there... : The final rise in temp is always relative to the ambient air temp. At : altitude, where temps can be quiet cool, you are getting a modest : "intercooler" effect. Additionally, amount of boost provided by the turbo : dramatically effects the temp delta. : As an example, a turbo pushing 10 psi, with no intercooler, may cause a : temp delta of 100' F (real world number), measured at the intake. If you : are at altitude, where ambient is quiet cold, say, 40-50' F., then the : intake temp, given the same boost, may only be 140-150'. Compare this to : take off, at sealevel, on a 95' F day, the intake charge may measure ~200' : F, given the same boost. 10 psi is a lot for a GA aircraft. 5 psi is more typical maximum boost (i.e. 40" MP) : Turbonormalized is a little bit different because the boost is going to be : much lower at take off than at altitude...nonetheless, you are still : getting an intercooler-like effect from the cooler ambient air. Only in the context of comparing the engine to ground-based racing applications. In the context of aircraft and density altitude, temperature rise is temperature rise. Barring unusual thermal lapse rate, the *effective* density altitude takes into account the decreasing temperature with altitude. -Cory -- ************************************************** *********************** * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * ************************************************** *********************** |
#23
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As you point out, the more compression the higher the temperature rise.
..The turbo is called upon to compress the air *more* as altitude goes up (and temperature goes down). Since the compressor efficiency of a turbocharger is less than 100% (actually about 70%), the air in the intake manifold is hotter then higher you go at any given manifold pressure. When I had a Turbo Lance with an aftermarket intercooler, there was a gauge that measured temperature before and after the intercooler and could give the difference as well. It was pretty apparent that all temperatures (CHT/TIT/intake before intercooler/intake post intercooler) went up with altitude if power was held constant. Mike MU-2 "Greg Copeland" wrote in message news On Tue, 04 Oct 2005 15:44:16 +0000, Mike Rapoport wrote: The heating of the intake and the consequent reduction in density is the reason that I think it will take more MP to produce the same HP at higher altitudes with a turbocharged engine. At the same MP/RPM a tubocharged engine is effectively running at a higher density altitude than a normally aspirated one. The turbocharged engine is also running at a higher density altitude as altitude increases at the same PM becasue there is more compression required, therefore more heating. The intake air is heated *substantially* and its density is reduced substantially. Natually, the effect is strongest at high manifold pressures and high altitudes. I agree that reduced pressure at the exhaust helps and an intercooler certainly helps too. Just tossing this out there... The final rise in temp is always relative to the ambient air temp. At altitude, where temps can be quiet cool, you are getting a modest "intercooler" effect. Additionally, amount of boost provided by the turbo dramatically effects the temp delta. As an example, a turbo pushing 10 psi, with no intercooler, may cause a temp delta of 100' F (real world number), measured at the intake. If you are at altitude, where ambient is quiet cold, say, 40-50' F., then the intake temp, given the same boost, may only be 140-150'. Compare this to take off, at sealevel, on a 95' F day, the intake charge may measure ~200' F, given the same boost. Turbonormalized is a little bit different because the boost is going to be much lower at take off than at altitude...nonetheless, you are still getting an intercooler-like effect from the cooler ambient air. Greg |
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