> Thanks for suggesting these interesting calculations, but I get slightly > different results. Not a lot different, but we're arguing over fairly > fine differences in already advanced technology so ten percent here and > there and pretty soon we're talking a difference between workable and > thermodynamically impossible.
Thanks for checking them! After spending a while cross checking all my calculations I found the problem, I'd stuffed up the final conversion from km to miles (multiplied instead of divided). Following that, I failed to sanity check the litres/km I was getting prior to conversion. > > First, we're using 1/2 rho A Cd v^2 and m g Urr for air and > rolling resistance, right? Yes > Then, diesel is usually quoted at 37-38 MJ/l while gas is 32-35 > MJ/l--- your 35.8 looks like an average?? Honestly? I googled for it - http://ies.jrc.ec.europa.eu/uploads/media/TTW_Report_010307.pdf - table 2.1 gives a LHV of 43.1, rho of 832 - hence 35.86. Or 32.184 for petrol. > I use STP air density at 1.17 kg/m3 and US gallons, and plug > everything into my favorite 'units' program: For some reason I assumed it was freezing - 1.3 for air density. Oops. 1.17 sounds more realistic. > > ((1/2) (1.17 kg/m3) 3m2 .33 (70 mph)^2 + 1200 kgf .015) 200 mpg / (37.5 > MJ/l) > > to get the ratio between required energy to maintain the speed, and > energy from fuel. Apparently 200 mpg would require 169% efficiency. > A 200mpg vehicle with your mechanical parameters can only do at most > 48 mph even if it had a 100% efficient engine; given a realistic > efficiency, we're talking 25mph max speed. > > Please look over those numbers and let me know if I'm off base here. They look good. I thought my original numbers looked too good to be true, oh well :D > > Greetings > > Przemek > ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite It's a free troubleshooting tool designed for production Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://p.sf.net/sfu/appdyn_d2d_ap2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
