Quote:
Originally Posted by NoD~
Something I have been pondering lately...
Lets say you have a 1.0L engine VS a 2.0L engine. They both use the same technologies, such as fuel injection, cam specs, etc. Lets assume for this comparison that they weigh the same. Efficiency is just about even on these engines.
In another realm, we have different gearing! One is the "performance" gearing and one has long, tall gears for low RPM cruising. Again, weigh the same, efficiency is equal.
So here is the question: If one is to do nothing but P&G with Engine off... is there really going to be any difference in the end result of MPG?
Here's my thoughts on it: If they both consume an equal amount of fuel to produce an equal amount of power and things like idling is thrown out of the equation, should engine size actually matter? And with gearing: As long as you stay in the appropriate RPM range (such as referenced to a BSFC), is there really any point in gearing changes as long as you don't cruise in a set gear?
Of course, in the real world, a 1.0L will probably weigh less than a 2.0L and you will have to occasionally cruise in gear, but I wanted to throw out the variables here and compare to see if drivetrains are really going to make the difference when doing the extreme and P&G+Eoff all the time.
Was just curious on some thoughts on this matter.
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If you're talking about pulse and glide with the engine off driving all the time,the real issue will be dodging all the bullets from irate and homicidal motorists who's mpg you're killing on city streets.Along with Earth,who might have to get a gun also.
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Academically:
*you'd have to specify a particular vehicle
*you'd have to specify a particular engine 'kill' velocity
*you'd have to specify a particular acceleration rate to reach your engine 'kill' velocity.
*The engine and gearing would be optimized for the highest BSFC under these specific conditions and they'd be optimized for only these conditions.
*if you drove any other way,performance would suffer
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*the larger engine would shrug off the acceleration ,operate at partial load,lower friction.
*the smaller engine would labor under acceleration,operate at a higher load fraction,higher rpm,higher internal friction.
*a small supercharged engine would become a 'larger' engine under boost for the acceleration phase.
*power IS power,but you'd have to analyze the efficiencies at which each powerplant developed the power band you sought.
*IC engines get their highest BSFC at a constant load,constant speed,rpm.They could see 33%thermal efficiency 'cruising',whereas 25% during transient loading.
*a recent Honda Accord with eAssist has no transmission.The engine operates only above 40-mph,and is directly coupled to the drive wheels right up to top speed (like many Bonneville racers [ 100% efficient power transfer])
*Pulse and glide would be the worst-case-scenario for an I.C. engine.