Originally Posted by
KnifeEdge_2K1
how do 3 cylinder engines work? i know atleast some 3 cylinder engines use the same intake, compression, combustion, exhaust cycle as most regular petrol engines. at any given time in an inline or boxer engine each piston will be in one of the four cycles, no 2 pistons will be in the same cycle, this is so that the piston undergoing combustion can power the rest of the cylinders and the car itself, in a 3 cylinder the only method i can think of making it work is to let teh rotational enertia do the work which would theoretically push the idle speeds higher, does this make any sense?
You're right with the rotational inertia.
The more cylinders the more overlap the bang cycle has and the smoother the engine is.
Some of thsi can be taken out by increasing the mass of the crank with offset weights and increasing the flywheel. Unfortunately the increased mass makes for slower acceleration of rpm AND REDUCTION in top end revs as the higher mving mass becomes more unstable.
This smooths out the engine at lowe engine speeds, reduce the weight and the engine becomes temperamental and hard to keep at a low idle ( lightened BDAs and Climax's being some of the worst/lumpiest )
All engines run the Otto cycle in each piston.
What an engine designer CAN play with is the timing of each cylinders cycle by position the big end on the crank relative to erach other.
Some triples actually run like a twin with 2 cylinders firing together, others spread them evenly. BUT a triple is hard to keep balanced and counter-rotatiing balancing shafts are needed to keep things revving smoothly at high speeds. Few bikes still run triples and some of the japanese micro-cars of the 80s used 600cc triples - basically their bike engines !!
This timing can be cltered by the engine designer. In cars it has become pretty much standard and no vairation beyond the accepted norm for I, H and V configurations.
Bikes, however, are playing with this at the peak end of the sport. MotoGp bikes are run with 4s running as twins, opposing 3 and 2s in 5s and 4v1 has been suggested as having been tried by Honda. These make BIG differences in bikes due to their low weight and alter dramatically the way the bike can use the tyre. It seems this isn't tried in cars, probably because the extra weight and larger tyre contact makes it irrelevant.
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'