CM871 Engine cycle...

[Rawze]

The Four stroke cycle of the CM871 Engine...

Terms...
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TDC = Top Dead Center (top of piston stroke).
BDC = Bottom Dead Center (Bottom of piston stroke).

BTDC = 'Before' Top Dead Center
ATDC = 'After' Top Dead Center
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In a four stroke cycle engine, four strokes of the piston are required to complete one cycle. The four strokes are...

Induction -- Clean air is pushed into the cylinder from the turbocharger (intake). The induction stroke starts when the intake valves open 10° before TDC, then air is drawn into the cylinder as the piston moves down. The inlet valve closes 1° before BDC.

Clean Air is Sucked In...






Compression -- The air is now trapped in the cylinder and as the piston rises on the compression stroke, the air is compressed. As the air is compressed, it rises in temperature.

That Air is then Compressed...





Power -- When the piston reaches about 19° before TDC (Adjusted by the ECM), the injection of fuel commences and continues until about 73° after TDC. The heat in the compressed air ignites the fuel and combustion takes place. The gases expand forcing the piston down, providing power.

The Piston Fires...






Exhaust -- The exhaust valves opens at 26° before BDC and the exhaust discharge as the piston rises again. Most of the exhaust gases have been discharged as the piston nears TDC. However, at 10° before TDC, the inlet valve opens to start the next Induction cycle. The rush of air that enters the cylinder, helps discharge any remaining exhaust gases until the exhaust valve closes at 3° after TDC.

Exhaust Gas Escapes...




As the next Induction cycle start, of coarse, The whole cycle is repeated.

The result, is that Power is only produced by any given piston every 'Other' cycle of the engine. This also means that for every two rotations of the crankshaft at the bottom, there is only one rotation of the camshaft(s) at the top (in the head).