REFLECTOR: Exhaust systems

Wed, 16 Jul 2003 08:26:15 -0600

Mike,

Because they are turning it faster, UNDERSTAND!!!!

The HP output of an engine will increase with RPM up to a certain point. 
   All engines have some curve that will give a certain HP for a certain 
RPM.  That's why a constant speed prop beats a fixed cruise pitch prop 
on take off.  The fixed pitch prop won't allow the engine to turn up to 
speed, thus the reduced HP.

Scott

Mike Pollock wrote:
> "The point I was trying to make is that the Franklin is 10 cubic inches
> smaller than the Lycoming, yet it has more certified horspower. Why?"
> 
> Because RPMxTorque = HP and the Franklin is getting its HP at the higher
> RPM.
> 
> Mike
> 
> -----Original Message-----
> From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
> Behalf Of Brian Michalk
> Sent: Tuesday, July 15, 2003 4:15 PM
> To: reflector@tvbf.org
> Subject: RE: REFLECTOR: Exhaust systems
> 
> 
> Certainly, fuel burns at a specific temperature at a specific condition.
> I was comparing carbureted engines(O360, not IO360) on purpose, because
> there doesn't exist a certified fuel injected Franklin against which to
> compare.  I could cite someone's homebuilt fuel injected Franklin dyno data,
> but that's only a single data point, and is not very relevant to the
> discussion.
> 
> The point I was trying to make is that the Franklin is 10 cubic inches
> smaller than the Lycoming, yet it has more certified horspower.  Why?  It's
> in the compression ratio, and the cam design.  Although the original topic
> was exhaust gas temperature, I'll keep my comments focused mainly on
> compression ratio, because I feel that is the reason for lower EGTs, and
> most of the power difference.
> 
> Increasing the compression ratio increases horsepower for the same amount of
> air/fuel.  But you are right, there is no free lunch.  The tradeoff is that
> the Franklin can only use 100 avgas.  Not good considering the future of
> 100LL. It's either that, or retard the timing to make sure detonation
> doesn't happen.  Retard the timing, more burning mass goes out the tailpipe,
> higher EGT's.
> 
> The Franklin is just a very efficient engine.  It keeps the fire inside the
> cylinders longer, and scavenges better, meaning a much better intake charge
> for the next bang.  EGT and BSFC usually are inversely proportional.  I can
> look up my engines book as it was run on the factory dyno and give you my
> BSFC.
> 
> The most efficient engine would have an EGT that is the same as the intake
> temperature.  That would mean 100% energy extraction from the fuel.  Where
> can I get one of those?
> 
> If you want, I can provide references.  I have a copy of Taylor, and
> Heywood.  I'm sure I can find a chart somewhere in the text relating some
> combination of EGT/torque/compression ratio/BSFC.
> 
> As a side note, I was talking to a NASA engineer years ago about
> experimental engines they were testing.  The engine was mostly carbon fiber,
> and ceramic.  There was no oil, and no cooling system.  Completely self
> lubricating.  They wanted to let the engine come up to combustion
> temperatures to extract as much energy from the fuel as possible.  He said
> they got some good BSFC numbers, but had problems with engines siezing, due
> to the expansion of various materials.  The fuel was very expensive too.  It
> had to resist pre-ignition due to the incredible heat.
> 
> 
>>-----Original Message-----
>>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
>>Behalf Of Scott Derrick
>>Sent: Tuesday, July 15, 2003 2:06 PM
>>To: reflector@tvbf.org
>>Subject: Re: REFLECTOR: Exhaust systems
>>
>>
>>Well, my IO360 is 200HP, so not much difference there.
>>
>>I think there's something fishy in Denmark about this A&P's remark.
>>
>>We are also not talking about cruise RPM's but takeoff rpms, which are
>>considerably lower.
>>
>>Any way you cut it, a specific air-fuel mix at a certain pressure burns
>>at a certain temperature. I don't care if its in a magic Franklin or not.
>>
>>Scott
>>
>>There's No Such Thing As A Free Lunch!
>>
>>Brian Michalk wrote:
>>
>>>Franklin engines are 10.5:1 compression ratio with 350 cubic
>>
>>inches, and are
>>
>>>rated at 220 horsepower, normally aspirated.  Compare this to a Lycoming
>>>0-360 rated at 180 horsepower.  More heat(energy) goes into the work.
>>>The second thing that could cause low EGT is the very high
>>
>>valve overlap.
>>
>>>There is a lot of scavenging going on in a Franklin cylinder, causing
>>>volumetric efficiencies of 103% at the cruise RPMS.
>>>
>>>
>>>
>>>>-----Original Message-----
>>>>From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
>>>>Behalf Of Scott Derrick
>>>>Sent: Tuesday, July 15, 2003 11:09 AM
>>>>To: reflector@tvbf.org
>>>>Subject: Re: REFLECTOR: Exhaust systems
>>>>
>>>>
>>>>This sounds very odd.  I think av gas in a near optimal
>>>>mixture(Stociometric?) burns at 1500+ F. It doesn't matter whether its
>>>>in your Honda Civic, your lawn mower or aircraft engine.
>>>>
>>>>Maybe its the placement of the EGT probe.  The absolute temp is really
>>>>of not much concern because where you stick the probe in and how the
>>>>exhaust flows in the pipe will effect the probe temperature quite bit.
>>>>Its the trend that is of prime importance.
>>>>
>>>>Scott
>>>>
>>>>John Dibble wrote:
>>>>
>>>>
>>>>>I just spoke with an A/P that works on Franklin engines.  He
>>>>
>>>>says I should not expect
>>>>
>>>>
>>>>>my EGT to exceed 1000 F.  Franklin engines run cooler.
>>>>>
>>>>>John
>>>>>
>>>>>steve korney wrote:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>>John...
>>>>>>
>>>>>>In that case your running way to rich...You should see temps of
>>>>>
>>>>about 1250
>>>>
>>>>
>>>>>>to 1300 (f) on take-off...
>>>>>>Maybe that's the reason it stumbles so much on run-up...Lean it
>>>>>
>>>>out...Keep
>>>>
>>>>
>>>>>>the temps above 1150 on the ground or you won't vaporize the
>>>>>
>>lead in the
>>
>>>>>>fuel and it will foul your plugs...
>>>>>>
>>>>>>Best... Steve
>>>>>>
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> 
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