An engine has 4 cylinders, each with 300mm diameter and piston stroke of 500mm. Effective pressure is 1200 kPa, operating speed is 300 rpm a?

Question

An engine has 4 cylinders, each with 300mm diameter and piston stroke of 500mm. Effective pressure is 1200 kPa, operating speed is 300 rpm and efficiency is .82. If there are two power strokes per revolution, calculate the output power of the engine?

Answer 1

So this is a 4-cylinder 2-stroke engine? Wierd...



300 rpm = 600 power strokes per minute = 600 stokes / min * 1 min / 60 s = 10 power strokes per s



Energy per power stroke = Pressure * change in Volume = 1200000 Pa * (pi*(0.300m )^2/4 * (0.500 m)) = 424 kJ per stroke



Power = energy / time = 424 kJ per stroke * 10 strokes per s = 4240 kJ/s = 4240 kW



Multiply by the efficiency

Power = 4240 kW * 0.82 = 3480 kW



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I messed up a little bit....



I was off on my energy calculation

Energy per stroke = 42.4 kJ per stroke



Power = 42.4 kJ / stroke * 10 strokes / s = 424 kW



I forget to multiply it by 4 - because of the 4 cylinders

4 cylinders = 424 kW * 4 = 1696 kW



Multiply by the efficiency = 1696 kW * 0.82 = 1391 kW



By the way... Change in volume = cross sectoinal area * bore stroke = pi*d^2/4 * bore stroke

Answer 2

Note : calcs done on excel, rounded to 0 decimal places on this reply (except for the answer)



300 rpm = 1 / (300/60) 0.2 seconds per rev of the crank



I’m seeing a four cylinder four stroke ( a normal car engine, with a two up two down crank , which gives a total of two power strokes per revolution of the crank)



So, the mean cylinder pressure * the cylinder area gives a force of :

84,823 N on the piston



The work done on 1 stroke = force * distance (cylinder stroke in metres)

= 42,411 Joules



There are two total power strokes per revolution of the crank, so, the total work done :

= 84,823 Joules



The crank power output is therefore :

Work done / time taken

= 84,823 / 0.2

= 221,057 Watts



Giving an actual drive power of

221,057 * 0.82

= 173,887.1534 Watts

(174 kW , 466 hp approx)



Sorry, the answer should be twice that amount. Messed up at :

work done / time taken



Sorry, not twice the amount, new from :

work done / time taken

= 84,823 / 0.2

= 424,115 Watts



Giving an actual drive power of :

424,115 * 0.82

= 347,774 Watts

(348 kW approx)



Sorry about that.

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Answer 3

Thanks for your help. The answer is actually 1391.2 kW but I don't know how to figure it out. LOL I HATE PHYSICS!!! not totally true, but very frustrating. Any other ideas?