Looking for a reference from an FCOM, AFM or other manual for the fuel consumption per hour in pounds or kilos of the Honeywell RE 200 APU on the CRJ900.
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It's surprisingly hard to come with that sort of data. It's hard to come up with a fuel burn number because the fuel burn varies widely, because the loads vary widely, between electrical loads and bleed demand. However, it's not too hard to come up with a theoretical maximum and estimate from that.
The best way to make an educated guess is to take the baseline HP rating of the Honeywell RE200 APU used in the CRJ7/900, around 325 hp, and work out the fuel burn at maximum power from the typical specific fuel consumption of turboshaft engines, which is somewhere around .5 to .6 lbs/hp/hr. Say to be conservative, we'll use .6 lbs/hp/hr.
So wide open, the APU will be burning .6 x 325, or just under 200 lbs/hr. It might get close to that if you are running all of the electrics off the APU gen and both packs.
Normally however, the demands are going to maybe 1/3 to 2/3rds of that. If it's idle, it might be burning 30-50, and with bleed loads due to running the AC packs, maybe 100-150.
So I think you could use 100-125 lb/hr as a ballpark value when you want to allow for fuel used by the APU while on the ground and providing air conditioning and powering the electrical system. Or if you just want to assume the worst case and go by that, for an hour of sitting on the ground with the APU running everything, you can safely assume it's going to use not more than 200 lb of fuel.
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$\begingroup$ I wonder what the site is referring to by "110 pounds per minute". Maybe they meant per hour? $\endgroup$– user14897Commented Mar 12, 2021 at 19:35
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$\begingroup$ I think it's an expression of bleed flow incorporating volume and pressure. Can't remember for sure now. It's been a while. $\endgroup$– John KCommented Mar 12, 2021 at 21:17
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$\begingroup$ Ah that makes sense, thanks. I like your approach to the answer; applicable to all future what's APU X's FF? Already +1ed ;) $\endgroup$– user14897Commented Mar 13, 2021 at 0:00
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2$\begingroup$ Yeah if you learn the SFC's of different engines, you can work out the burn for pretty much any power setting if you know the HP being made. .5-.6 for turboshaft/turboprops, about .45 for carbureted piston, maybe low .4s for injected piston, high .3s for modern cars, low .3s for diesels. The turbo compound Wrights were extremely fuel efficient, actually down in the car range. I seem to remember it was something like .38. Each engine had what amounted to two Lyc O-320s helping it out for free (each exhaust power recovery turbine made about 150 hp x 2). $\endgroup$– John KCommented Mar 13, 2021 at 1:27