Aircraft Engine Power

[wailunwu]

HI

Assuming even distribution of fuel and air in the engine, why is peak/best engine power not at peak EGT (with stoichiometric fuel to air ratio 14.7 to 1)? I was told that best power is at a slightly rich fuel to rich ratio.

If 14.7:1 gives the most efficient combustion (with no excess fuel/gas) why doesn't the engine power peak at this point?

Please see link below:

http://www.mummbrothers.com/SRF_Stuff/images/Stoich.gif

Thanks
Al

 

[GregLocock]

Most engines are limited by how much air they can ingest. Therefore to maximise power in order to use every bit of oxygen that is available slightly rich mixture is needed. The extra fuel tends to reduce EGT. Similarly for best economy you want to burn every scrap of fuel, so excess air is required.

Cheers

Greg Locock


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[VEBill]

In other words, this assumption ("Assuming even distribution of fuel and air in the engine") is not true.

 

[wailunwu]

@greglocock

However, mathematically speaking, should max power be at 14.7:1 (stoichiometric) ratio? The power curve should theoretically peak at 14.7:1 air-fuel ratio since both fuel and air are used up, correct?

 

[imcjoek]

Stoichiometric at full load would require rather low compression and/or retarded timing to prevent knock. That isn't so hot for max power output either.

 

[GregLocock]

No, it would only be 14.7 if that burnt all the oxygen to CO2. It doesn't.

Cheers

Greg Locock


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