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Re: Vapor Engine can get 100MPG+ thoughts? Posted by JimBlake [Email] (#141) [Profile/Gallery] (more from JimBlake) on Tue, 6 Dec 2011 06:44:42 In Reply to: Re: Vapor Engine can get 100MPG+ thoughts?, TML [Profile/Gallery] , Mon, 5 Dec 2011 05:59:26 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Air is the working fluid, not the "fuel". It's pretty much the (almost inert) nitrogen that is compressed, heated, & expanded to operate the engine. The fuel & oxygen simply provide the heat input.
Lots of talk about friction, or heat losses, when the big thing that drives thermal efficiency is the heat rejection of the cycle. That's not the same as simple heat loss. The Otto cycle isn't the same as the Carnot cycle, but the same stuff applies only more so. You have to reject some heat in order to make it work.
Throttling an Otto-cycle engine really kills efficiency, because you're messing with the pressure ratios & not just the temperature ratios. Efficiency goes down as heat rejection goes way up. If you could supply less heat (less fuel) while keeping the throttle wide-open, you'd be better off. Problem is, that doesn't work. Go lean and it has problems like detonation. Go more lean & it won't ignite. If water injection can allow you to get around this, maybe there's something to it.
OTOH, a diesel operates without throttling. They just cut back the fuel without throttling the air. The advantage is operating at lower power without the efficiency-robbing throttle.
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