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Posted by: TimT Jul 6 2004, 05:54 PM

http://www.avweb.com/news/columns/182132-1.html

Posted by: ArtechnikA Jul 6 2004, 08:44 PM

as i'm sure you're aware, AVWEB, John Deakin, and George Braly (both of whom i've met...) are very well respected in the aviation community.

as you can infer from that GAMI/P&W, not everything scales as well as we'd like, and there are differences between what happens in very large, very slow, relatively low-compression engines and what happens in our small, fast, relatively higher compression engines.

the relationship between power, EGT, and CHT is at times nonobvious but it's also one that's been around for a while. the GAMI/P&W chart looked pretty much like i thought it would from hearing Jake (and others) describe the dyno tuning relationships. still cool to see it in chart form, tho...

Posted by: anthony Jul 6 2004, 08:54 PM

Can we get a glossary? :-)

LOP
ROP
TBO
MP
OAT
JPI

Posted by: ArtechnikA Jul 7 2004, 10:22 AM

Lean Of Peak (EGT)
Rich Of Peak
Time Between Overhaul
Manifold Pressure
Outside Air Temperature
JPI - a sophisticated engine guage.

i'm not familiar with the JPI, but there's a very nice unit called the 'GEM' (Graphic Engine Monitor) that shows both CHT and EGT data per cylinder on a bargraph display. makes it very easy to tune based on load, temperature, and fuel flow. (load - via variable pitch propellor - kind of like a continuously variable transmission in a car - and fuel flow - via the mixture knob - are easily adjustable in operation by controls for this purpose)

Posted by: ArtechnikA Jul 7 2004, 10:28 AM

one reason we don't run Lean OF Peak on the ground is that in that region, it's hard to keep oxides of nitrogen (NOx) under control without a catalyst, which our cars (mostly) and aircraft (due to leaded fuel among other things) don't have.

the various lean-burn engine management systems and - lately - the gasoline direct-injection - engines are all attempts to burn in the borderline Lean Of Peak region.

Diesels always operate in an excess of air and nowadays they are able to achieve their very high efficiencies and power levels through the use of very large amounts of exhaust-gas recirculation. recirculating exhaust gas (basically inert) reduces the excess of oxygen that can lead to high combustion temps (high EGT...) and high NOx levels.

it's also hard to get an engine running LOP to accellerate. aircraft spend A LOT of time at cruise, but the automotive power cycle is far more transient...