Received-SPF: pass
 receiver=logan.com; client-ip=17.158.233.229; envelope-from=markmcclure@me.com
MIME-version: 1.0
Content-transfer-encoding: 7BIT
Content-type: text/plain; CHARSET=US-ASCII
From: Mark McClure <markmcclure@me.com>
Subject: engine exhaust
Date: Thu, 26 Jan 2012 20:27:48 -0800
Message-id: <0A166277-6F87-4A51-BF4A-9459D5416A39@me.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>

Ok bare with me here, I have been digging through all my old engineering books trying to answer this but have come to no intelligent answer.

I work behind turbines a lot and they are wonderful when they are needed - but the fuel guzzling just makes them ill suited for our needs - enter the rotary. But in designing my engine I am curious about using some theories from the turbine. 

For this reference I am using a 420hp C-20J Turboprop (just because it is the smallest I have used)

Approximately 70% of the energy is used to turn the compressor and accessories and 30% is used for actually turning the output shaft. Of that compressed air only 25% is used in combustion while the remaining 75% is routed around the combustion chamber for cooling. 

The compressor is a six stage axial, single stage centrifugal. Compressing the air 6.5 times and the temperature is about 500F. The TOT (also TGT or ITT, measured between the gas turbine and power turbine) is 1500F. 

The 13b MSP is putting out exhaust temps of 1600F. So using the same principles in reverse, the remaining energy powers a compressor (turbo) and that air is then used to assist in the cooling. 

So the question is: What have I oversimplified?

Mark


Glasair SII - 30% complete
13b MSP - 5% complete