Turbo performance vs non-turbo

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...
jmk wrote:
: Right. A turbonormalized engine never sees any more pressure than one
: that is normally aspirated - it just sees it up to a high altitude.
: Cooling (at high altitudes) may be an issue, but not cylinder pressure.

Actually, technically speaking, running the same MP at higher altitudes
will
produce a little more power than at lower altitudes. The lower ambient
pressure
reduces backpressure on the exhaust, so there's more scavanging and a
bigger intake
air/fuel charge for the same MP.

I saw that in the performance specs on a friend's normally-aspirated
PA-24-250. Something like equal power is between 1-2" different MP at
12000' vs. sea
level (RPM constant). I don't remember the exact numbers, but that's in
the ballpark.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************


It doesn't work that way with a turbocharged engine since the ingested air
is heated by compression.

Mike
MU-2

Mike Rapoport wrote:

: It doesn't work that way with a turbocharged engine since the ingested air
: is heated by compression.

I would argue that it still works that way. In addition, however, the heating
of the intake air reduces the effective mass on the intake charge. Whether one or the
other dominates or they cancel each other out depends on lots of factors... in
particular an intercooler.

I'm not being argumentative... just sharing info that I'd never thought of
before. It doesn't make a huge difference, but it does make a difference. Running
24/24 doesn't *always* make the same power or burn the same fuel. Altitude and
mixture both have 10-20% adjustment fudge factors in there.... throw in a turbo with
heating and there's another 10-20% in the mix as well.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote in message
...
Mike Rapoport wrote:

: It doesn't work that way with a turbocharged engine since the ingested
air
: is heated by compression.

I would argue that it still works that way. In addition, however, the
heating
of the intake air reduces the effective mass on the intake charge.
Whether one or the
other dominates or they cancel each other out depends on lots of
factors... in
particular an intercooler.

I'm not being argumentative... just sharing info that I'd never thought of
before. It doesn't make a huge difference, but it does make a difference.
Running
24/24 doesn't *always* make the same power or burn the same fuel.
Altitude and
mixture both have 10-20% adjustment fudge factors in there.... throw in a
turbo with
heating and there's another 10-20% in the mix as well.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************


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.

I don't have a flight manual for a turbocharged airplane here but hopefully
somebody here does.

Mike
MU-2

: 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.

: I don't have a flight manual for a turbocharged airplane here but hopefully
: somebody here does.

I agree completely. The heating can be quite substantial from what I've read.
If there's no intercooler, I suspect that you probably always lose the added
scavanging HP to lower density incoming air at the elevated temperature as you
suggest. If there's an intercooler, things might trade off differently and equiv
MP/RPM combination at altitude might be less than, more than, or equal sea-level power
at the same MP/RPM combination.

Between the (substantially) higher inlet air temperature, decreased cooling
due to thinner air flow over the cylinders, and the ability to maintain very long,
high-power climbs, it's no wonder turbo'd engines eat cylinders routinely. The stock
turbo Arrow system is particularly bad... throttling full boost at the inlet? Pretty
stupid to compress the intake only to throw away most of it.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

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

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 *
************************************************** ***********************

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