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The amount in crankshaft degrees by which the valves open before top dead centre or bottom dead centre is reached is known as valve lead. The amount in crankshaft by which the valves close after top dead centre or bottom dead centre is reached is known as valve lag. Valve overlap is a secondary means to cool exhaust valves with intake air ...
A desmodromic valve is a reciprocating engine poppet valve that is positively closed by a cam and leverage system, rather than by a more conventional spring. The valves in a typical four-stroke engine allow the air/fuel mixture into the cylinder at the beginning of the cycle and exhaust spent gases at the end of the cycle. In a conventional ...
Top dead center in a gasoline engine. In a reciprocating engine, the dead centre is the position of a piston in which it is either furthest from, or nearest to, the crankshaft. The former is known as top dead centre (TDC) while the latter is known as bottom dead centre (BDC). [1] Position of pistons
This is because the big end of the connecting rod swings from side to side, so that the motion of the small end deviates from ideal sinusoidal motion between top and bottom dead centre on each swing, i.e. twice per crank revolution, and the distance the small end (and a piston connected to it) has to travel in the top 180° of crankshaft ...
This stroke of the piston begins at top dead center (T.D.C.) and ends at bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position while the piston pulls an air-fuel mixture into the cylinder by producing a partial vacuum (negative pressure) in the cylinder through its downward motion.
Just as with a boxer-four, piston pairs from opposite banks reach top-dead-centre at the same time, but with a crankpin split of only 60° instead of 180°, potentially giving a shorter and stronger or stiffer crankshaft. For 60° V6s, the crankpins are usually split the other way causing the paired pistons to reach top-dead-centre 120° apart.
Pressure in cylinder pattern in dependence on ignition timing: (a) - misfire, (b) too soon, (c) optimal, (d) too late. In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.
Diesel engine operation on the other hand inhales and compresses air only by the motion of the piston moving to top dead centre. At this point maximum cylinder pressure has been reached. The fuel is now injected into the cylinder and the fuel ' burn' or expansion is started at this point by the high temperature of the, now compressed, air.