On Tuesday 11 December 2012 09:46:10 Eric van den Berg wrote: > I see. > Looking at the code (I think) I can see you are trying calculate the > pressure losses in the injector/throttle valve, "airbox" and inlet tubes. > Using throttle position and engine speed (was expecting cylinder > displacement here also).
The displacement is somewhat irrelevant in that it is a constant and can be ignored. The modeler provides two data points; the pressure at full throttle and maximum RPM, and the pressure at 0 throttle and idle RPM. These are used to determine the impedance of the airbox and throttle respectively. In this scheme, the engine is also treated as an impedance which varies with ( 1 / engine speed ) giving infinite impedance at 0 RPM[1] and falling towards, but never reaching, 0 impedance as engine speed increases. We experimented with many other and more complicated intake models early on, and this is the best behaved of the lot. > Basically your MAP at idle is to low, thus the > pressure loss too high. As 99% of the pressure loss comes from the > injector/throttle position, I would say for idle power setting the injector > air valve should be a bit more open? > I assume it is only calculated for indication and not for engine power > calcs? Actually, the manifold pressure is used in three ways in the power calculations. First, it affects the mass flow rate. We assume an adiabatic process so the loss in pressure is accompanied by a corresponding loss of density. Second, the volumetric efficiency is reduced by the intake pressure being less than the exhaust pressure further reducing the mass flow rate. Finally, the pressure difference between intake and exhaust creates a direct power loss as work is performed to pull and maintain the manifold pressure drop. Ron [1] Note: Engine speed actually used is mean pistons speed not RPM. ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
