In a normal piston-cylinder combustion engine is it more beneficial to have a larger bore and fewer cylinders or smaller bore with more cylinders? or does it cancel out?
In: Engineering
It really depends on the application. Surprisingly there is no overall optimal engine design. Every engine makes tradeoffs. This one might be small, light and powerful – but it’s expensive and doesn’t last long. This one might be super efficient, but isn’t very responsive. This one might be amazing in all aspects, except its really polluting so needs an expensive aftertreatment solution.
Generally:
A long stroked engine with fewer big cylinders can be more efficient and produce a decent amount of torque at low speeds for a given displacement (Big truck diesel – lots of torque and good efficiency)
A short stroke engine with more little cylinders can rev fast and be power dense, but sacrifices low speed torque and often doesn’t last as long. (motorbike – lots of power from a tiny engine).
A short-stroke big cylinder engine is unusual. The reciprocating mass is too high to rev it fast, and you don’t gain the efficiency benefit of the long stroke.
A long stroke small bore is difficult/impossible to make because the conrod hits the cylinder wall.
Then there are considerations like low cylinder counts are quite unbalanced and don’t sound great. This is why car engines are generally 3 or more cylinder.
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