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b5b0ba5eba
temperature. The cylinder head is assumed to be at uniform temperature. Obviously this is incorrect, but it simplifies things a lot, and we're just looking for the behaviour of CHT to be correct. Energy transfer to the cylinder head is assumed to be one third of the energy released by combustion at all conditions. This is a reasonable estimate, although obviously in real life it varies with different conditions and possibly with CHT itself. I've split energy transfer from the cylinder head into 2 terms - free convection - ie convection to stationary air, and forced convection, ie convection into flowing air. The basic free convection equation is: dqdt = -hAdT Since we don't know A and are going to set h quite arbitarily anyway I've knocked A out and just wrapped it up in h - the only real significance is that the units of h will be different but that dosn't really matter to us anyway. In addition, we have the problem that the prop model I'm currently using dosn't model the backwash from the prop which will add to the velocity of the cooling air when the prop is turning, so I've added an extra term to try and cope with this. In real life, forced convection equations are genarally empirically derived, and are quite complicated and generally contain such things as the Reynolds and Nusselt numbers to various powers. The best course of action would probably to find an empirical correlation from the literature for a similar situation and try and get it to fit well. However, for now I am using my own made up very simple correlation for the energy transfer from the cylinder head: dqdt = -(h1.dT) -(h2.m_dot.dT) -(h3.rpm.dT) where dT is the temperature different between the cylinder head and the surrounding air, m_dot is the mass flow rate of cooling air through an arbitary volume, rpm is the engine speed in rpm (this is the backwash term), and h1, h2, h3 are co-efficients which we can play with to attempt to get the CHT behaviour to match real life. In order to change the values of CHT that the engine settles down at at various conditions, have a play with h1, h2 and h3. In order to change the rate of heating/cooling without affecting equilibrium values alter the cylinder head mass, which is really quite arbitary. Bear in mind that altering h1, h2 and h3 will also alter the rate of heating or cooling as well as equilibrium values, but altering the cylinder head mass will only alter the rate. It would I suppose be better to read the values from file to avoid the necessity for re-compilation every time I change them. |
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| docs-mini | ||
| src | ||
| tests | ||
| acconfig.h | ||
| aclocal.m4 | ||
| acsite.m4 | ||
| AUTHORS | ||
| ChangeLog | ||
| config.guess | ||
| config.sub | ||
| Done | ||
| FlightGear.dsp | ||
| FlightGear.dsw | ||
| Makefile.am | ||
| NEWS | ||
| README | ||
| Thanks | ||
Welcome to the FlightGear Flight Simulator project. =================================================== The primary web page for this project is: http://www.flightgear.org For basic installation instructions see the "INSTALL" file. Before you can run FlightGear you will also need to download and install the "base" package which is a collection of textures, sounds, sample scenery, and other data files need by the sim. For additional install help for specific platforms please browse the "docs-mini/" subdirectory. More complete documentation is available from our web page as a separate distribution. Please take a look at the "Thanks" file for a list of people who have contributed to this project. If you have contributed something but don't find your name in this file. Please send a polite reminder to curt@flightgear.org For a summary of changes/additions by version see the "NEWS" file. This project is GPL'd. For complete details on our licensing please see the "COPYING" file. For information on available mailing lists, mailing list archives, and other available source code and documenation, please visit our web site. FlightGear is a product of the collaboration of large international group of volunteers. FlightGear is a work in progress. FlightGear comes with no warrantee. We hope you enjoy FlightGear and/or find it of some value!