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  #11  
Old 07-10-2015, 08:42 AM
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aturner aturner is offline
 
Join Date: Jan 2005
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I would be interested in understanding the tradeoffs involved with using .028 vs. .025 as a baseline size.
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  #12  
Old 07-10-2015, 09:09 AM
ReidVaitor ReidVaitor is offline
 
Join Date: Jun 2006
Location: SoCal
Posts: 174
Default Lower CHT

From the feedback I have received having 400F plus on climb is totally normal, but there is always a desire to lower my CHT being is a rather warm area 12 months out of the year (aka Southern California) I too wonder what effect having a smaller orifice has on CHT? all I can think is less fuel, less combustion, less heat (aka lean of Peak) I am at .3 spread and the engine runs wonderfully, just hot on climb.
Anxiously awaiting feedback from Don!
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  #13  
Old 07-10-2015, 09:23 AM
BillL BillL is offline
 
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Location: Central IL
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Quote:
Originally Posted by 1001001 View Post
No expert here, but I i would think that it was a balancing act. The absolute orifice sizes would be less important than the relative change in size between the richer and leaner cylinders while maintaining total flow at a constant pressure drop.
Very much agree. Diesel orifices are much the same. For example, an abrasive slurry, (looks and acts like silly putty) is pushed through the nozzles to radius the inlet to each orifice. Delivery by each orifice is then stabilized to it's diameter.

Although our systems are much lower pressure, the same principles apply. Flow variations due to micron sized manufacturing differences certainly exist, and overpower the direct link to diameter unless a similar (expensive) process was/is used.

Disclaimer: I have no personal knowledge of the manufacturing processing of the orifices for our aircraft engines. If someone does, please add to our knowledge.
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  #14  
Old 07-10-2015, 09:39 AM
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Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Quote:
Originally Posted by ReidVaitor View Post
I too wonder what effect having a smaller orifice has on CHT? all I can think is less fuel, less combustion, less heat (aka lean of Peak) I am at .3 spread and the engine runs wonderfully, just hot on climb.

The flow -------and thus the CHT------is set with the red knob.

The balance is set with the individual injector nozzle insert. This is what equalized the CHTs.
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Last edited by Mike S : 07-10-2015 at 09:41 AM.
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  #15  
Old 07-10-2015, 10:53 AM
Don at Airflow Don at Airflow is offline
 
Join Date: Jun 2006
Posts: 316
Default A complex calculation

To understand why we choose what size nozzles orifice or how we manufacture our injector nozzles is a discussion left for our FI-101 class. You have to understand the theory of operation of the fuel control unit, the operation of the flow divider and the interaction of the fuel control, flow divider and injector nozzles to determine all this. Its pretty in depth to explain this is a few paragraphs.

Don
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  #16  
Old 07-12-2015, 04:03 PM
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RV10inOz RV10inOz is offline
 
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Location: Brisbane Qld. Aust.
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The secret to getting reasonable CHT's is not to monkey with the injectors unless you know what you are doing. Basically there is Don Rivera at Airflow Performance, Andrew Denyer at Riverina Airmotive(for the Aussies) and of course GAMI in Ada OK.

Once you get the Fuel/Air ratio's balanced, then and only then can you start looking at the baffles etc.

As Don mentioned above it is all about getting consistent F/A ratios first. Then get the average cooling right and do not sweat a 20dF or there about variation in CHT.
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