Kurt Nolte wrote: > On 10/16/05, *Jeromie Reeves* <[EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]>> wrote: > > How about a rotary engine that doest take those delicate graphite > seals? > Long story short > I had one via my lil brother that only had 1 working cell and > still put > out enough HP to go > 85mph. > > Jeromie > > > From what I understand, a rotary engine is actually a step /down/ in > thermal efficiency; maybe it's just the materials used, but I seem to > hear something about how they may have more power density, but their > thermal efficiency suffers too much to really make them widespread.
It's not the materials used, it's that there is so much surface area per unit of volume. All the extra surface area absorbs heat, which is wasted out the cooling system, and quenches the flame which increases pollutants. Rotaries (wankels, at least) are well suited for aircraft use in some ways - they're light, powerful, smooth, and reliable. Their failure mode tends to be losing power gradually, as opposed to piston engines that fail catestrophically when they seize up or break a piston or swallow a valve or the timing belt breaks. Unless you have something like an airplane, however, they're usually too thirsty to take seriously. > Maybe when rotaries have more research put into them like the piston > engine has they'll meet and even exceed the efficiency and power > density of reciprocating piston engines, but right now I don't believe > they're there yet. Besides which they are, as you have just implied, > rather delicate as opposed to the near brash ruggedness of a RP engine. Unless research leads to materials that simply don't need to be cooled (the adiabatic diesel is a long time dream in the military) I wouldn't get my hopes up. I also wouldn't get my hopes up on the other rotary and unconventional designs with cam-type camshafts. I'm a little surprised no one mentioned the dynacam (http://www.dynacam.com) which has been six months from the market for several decades IIRC. Internal combustion and sliding vanes present seal problems that aren't going to be fixed by a shade-tree mechanic of any kind. Sorry, but that's life. Opposed piston engines, OTOH, have some real advantages. Getting rid of the head and valve train simplifies things somewhat, and having hot pistons facing each other eliminates two heads and the heat loss associated with them. The Germans used opposed piston diesels in Junkers transport aircraft and could fly all the way to Brazil without refueling. Fairbanks Morse still makes them - see http://www.fairbanksmorse.com/engines/commercial/op/op_data.htm > Personally I'm a gas turbine fan, but I don't see them overtaking > everything and replacing all other engines anytime soon, so I figured > I might as well get with something people are a little more familiar > with. ;p Simple rotating devices have a big attraction:) The biggest drawback with turbines is that major parts of the engine that are under severe stress must operate at the peak combustion temperature. Unfortunately this guy named Carnot passed a law that said lower peak temps would operate at lower efficiency, so they won't be able to match diesels for efficiency until we make some, uhh, remarkable advances in materials:) Hope someone finds this interesting. I know a lot more about engine design than making biodiesel so far. --- David _______________________________________________ Biofuel mailing list Biofuel@sustainablelists.org http://sustainablelists.org/mailman/listinfo/biofuel_sustainablelists.org Biofuel at Journey to Forever: http://journeytoforever.org/biofuel.html Search the combined Biofuel and Biofuels-biz list archives (50,000 messages): http://www.mail-archive.com/biofuel@sustainablelists.org/
