# Internal combustion engine calculation questions

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Hello everyone I have some questions on engine calculations that I need help in please.

1) A reciprocating internal combustion engine operates on a 4 stroke cycle. If the engine's crankshaft is rotating at 5,985 rev/min, calculate the number of engine cycles completed every second

(note that I tried 5985/60 and that gave me a wrong answer)

2) An engine has a crank radius of 41mm. If the engine's crankshaft is rotating at 2131 rev/min the calculate the mean piston speed (m/s)

3) For an engine:
-Operating at speed of 2151 rev/min
-Having a crank radius of 41 mm
-Having a connect a connecting rod length of 136 mm
When the crankshaft has rotated 84 degrees from top dead centre, calculate the velocity of the piston, u (m/s), in the x-axis direction.

(why isn't the velocity 0 m/s since the piston only move in the y axis?)

4) An engine has the following geometry:
-A bore of 75 mm
-A stroke of 70 mm
-A ratio of connecting rod length to crank radius of of 3.8 m/m
Calculate the rate of change of volume (m^3 / rad) when the crankshaft has rotated -30 degrees from top dead centre

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CWatters
Homework Helper
Gold Member
1) A reciprocating internal combustion engine operates on a 4 stroke cycle. If the engine's crankshaft is rotating at 5,985 rev/min, calculate the number of engine cycles completed every second

(note that I tried 5985/60 and that gave me a wrong answer)
You calculated the number of engine revolutions per second. The question asked for the number of cycles per second. Look up how a 4 stroke works and find out how many revolutions there are per cycle. It's not 4.

Nidum
Gold Member
CWatters
Homework Helper
Gold Member
(why isn't the velocity 0 m/s since the piston only move in the y axis?)
Perhaps its flat 4 or V8 ? Is there a diagram to go with the question? Otherwise how do you know which is the x and y axis?

You calculated the number of engine revolutions per second. The question asked for the number of cycles per second. Look up how a 4 stroke works and find out how many revolutions there are per cycle. It's not 4.
I thought about it. I believe the correct answer is RPM/4/60 to get cycles per second.

May I ask help for the other questions as well?

CWatters
Homework Helper
Gold Member
It's not 4.

It's not 4.
Sorry sorry I meant RPM/2/60

CWatters
Homework Helper
Gold Member
That's better :-).
1 cycle = 2 revolutions = 4 strokes

That's better :-).
1 cycle = 2 revolutions = 4 strokes
Thanks :) can you please provide me with help for the other questions please?

berkeman
Mentor
Thanks :) can you please provide me with help for the other questions please?
You were warned in your previous thread (now deleted) to show your work and post using the Homework Help Template. You re-posted your questions and only showed a small amount of work on some of them. That is not acceptable here.

Post one question per schoolwork thread, and use the Homework Help Template that you are provided to show your work on the problem. This thread is closed.