Hp Calculation Help Needed Please

[bill barlow]

An engine crankshaft has a throw of 17mm.The piston exerts a force of 800kg at 2500rpm.What is the theoretical hp?

[factor-fiction]

By force do you mean the Torque?
HP=(RPM * T) / 5252?

[factor-fiction]

Sorry, I realise you do mean Force not torque

[dr b]

HP = 2(pi)(T)(RPM)/33000

T = torque = force x radius

everything must be in foot-pounds

[bill barlow]

No Mark. Imagine the 800kg as weight.

[factor-fiction]

Torque = force x radius
Then put that into the formula.
I'll leave you to crunch the numbers

[dr b]

nice straightforward explanation here:

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=ENG17504

[bill barlow]

Sorry my answer to Mark should be to factor-fiction

[Teddio]

Circumference = 0.107m
Force = 8000N
Work = Force X Distance = 8000 X 0.107 = 855J

Crankshaft frequency = 2500/60 = 41.7 Hz
Crankshaft period = 1/41.7 = 0.024 second

Power = Work/Time = 855/0.024 = 35625 Watts = approx 48 Horsepower

This assumes the piston is exerting a constant force of 8000N for the entire 360 degrees of revolution of the crankshaft which is unlikely.

[jomifl]

An adjustment to teddio's formula is needed to account for the average proportion of a revolution that is a power stroke and sine correction for the conversion of linear motion to rotation. In addition the connecting rod angle changes throughout the power stroke so the 800kg force is only realised at the top and bottom of the stroke when no rotary motion is imparted. The length of the connecting rod has to be known too.

[jim360]

Another adjustment is needed because 17mm =/= 0.107m...

[Teddio]

Jim, if the throw or radius is 17mm or 0.017m then the circumference will be 0.107m.