One major way acceleration hurts is that engines are set to richen the mixture during hard acceleration in order to prevent detonation (knocking, pinging) at high cylinder pressures.
Also, carburated engines richen the mixture to compensate for fuel vapour condensing on the intake manifold walls as manifold pressure increases when the throttle is opened. Doug Woodard St. Catharines, Ontario, Canada On Tue, 13 Sep 2005, Joe Street wrote: > > > Zeke Yewdall wrote: > Snip > > >I think for otherwise identical cars, a medium sized engine (but > >smaller than what most cars come with nowdays) will get better > >mileage, because it can accellerate fast enough to get out of the fuel > >dumping acceleration, and into more fuel efficient cruising faster. > > > > > If you accelerate you are doing work. If you accelerate slowly you use > less fuel per unit time but for a longer time. If you use high > acceleration you use more fuel per time but for a shorter time. However > definitely the frictional losses are higher when the engine is asked to > produce high torque, thus dropping the efficiency. > > >But if it's to large, it's less efficient at cruising speed because of > >low part load efficiency. And if it's too small, it it always trying > >futiley to accellerate, instead of cruising. Also, due to real fixed > >ratio transmissions, a less powerful engine may spend more time at a > >higher RPM, where the fuel efficiency in grams/kWh is less, whereas a > >higher power engine could downshift sooner. > > > > > The engine turning at higher rpm is not necessarily using more fuel. It > depends on the power the engine is producing and other factors including > thermal efficiency, bearing friction etc. There are a family of curves > for the engine showing torque vs rpm, power vs rpm and fuel consumption > vs rpm at a given load. For instance years ago one of the bikes I used > to ride got better fuel economy on the highway by driving in 4th gear at > higher rpm than in 5th gear at a lower rpm for the same highway speed. > > Joe _______________________________________________ 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/
