I.C engines at rest

I.C engines at rest

zaveri

Member

Updated: Oct 26, 2024

Views: 1.3K

Now here i am talking about those 4-stroke single cylinder petrol engines for two-wheelers.

now the question is that when the engine is stationary, then what exactly are the positions of the moving parts.(piston, crankshaft & connecting rod).

my guess is that the piston rests exactly at the center of the cylinder wall , and its position can be described as : (T.D.C + B.D.C)/2.

is this right ?

if not then what do you think are the exact positions ?

also when the engine is kick started, how does the piston move, (that is from from TDC to BDC or vice-versa) ?

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atul-namdeo

Member • Mar 30, 2013

i guess piston moves TDC to BDC.

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viky1147

Member • Apr 1, 2013

I guess there is no position prescribed or specifically designed for it. TDC and BDC is for performance study. Since there will be a clearance volume between the cylinder head and the piston top, the crank will be rotated even when the piston is exactly on TDC. For prescribing the position of the piston when the engine stops... The <a href="https://www.google.co.in/search?hl=en&q=necessity&spell=1&sa=X&ei=fX9aUb3lHcf0sgbt54HoCA&ved=0CC4QvwUoAA" target="_blank" rel="nofollow noopener noreferrer">necessity - Google Search</a> level is low and designing cost is higher. Hope it helps you 👍

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Gurjap

Member • Apr 2, 2013

I don't imagine the piston would go to any specific position once the ignition is shut off. It may come to rest anywhere between the TDC and the BDC once friction wastes all the kinetic energy it had.

As for starting the engine, a starter motor will crank the ring gear on the flywheel periphery at around 100 RPM until the engine's 4 stroke cycle becomes self sustaining.

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Khan Sakib

Member • Apr 2, 2013

I think it would not stop at particular position

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zaveri

Member • Apr 4, 2013

#-Link-Snipped-# #-Link-Snipped-# #-Link-Snipped-#

so you guys say that the piston comes to rest at any position.

but i don't think so, because the counter weight present with the crankshaft may not allow this.

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Gurjap

Member • Apr 4, 2013

Alright then. Consider a Vertical, Single cylinder IC engine. Suppose it was running and you turn off its ignition.

Now what is going to happen? It's going to run for a while, compressing air and blowing it out the exhaust, essentially wasting the momentum that it had built up. It will run out of that though, and soon a time will come when it will start compressing air but not quite finish, and what then? The counterweight is swinging downwards, and the piston is moving up, but since the momentum is exhausted, depending upon the size and displacement of the engine and the timing of when it was shut off the piston might as well stop anywhere in the cylinder.

And this is just one scenario. A somewhat similar one might play out with the exhaust stroke instead of the compression stroke.

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viky1147

Member • Apr 6, 2013

#-Link-Snipped-#
Just imagine with simple physics buddy. when u switch off the engine the fuel connection is cut. piston, crank etc is still in a movement, balances the opposing force and gets seized in its comfortable position. no major engineering in it. hope I am clear with ur question this time. 😀

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The Observer

Member • Apr 8, 2013

when it is kick started....i guess it is at the BDC when the kick lever is on its top. When u give it a downward push, it inturn moves the piston to TDC thereby compressing the air n some fuel-air mix being fed in and followed by the spark in the ending. If the combustion becomes self-sustaining then the engine continues on its way else if not the piston is thrown back and that is why you feel a return jerk. The jerk is because nothing is available to hold the compressed air and so the air pushes the piston back and you'll have to try the kick again.

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riteshbstkr

Member • Apr 18, 2013

The piston is at TDC when vehicle at rest
because the flywheel is at lowest due to its weight
whenever kick is apply flywheel move upward and piston is at downword and suction done

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