![]() Please let us know your thought in the comment section below.įiled Under: I.C Engines, MECHANICAL ENGINEERING Tagged With: I. this will lead to the bad performance of the engine. ConclusionĪ well-tuned port timing diagram will result in the better performance of the engine. similarly, if the engine port timing is not set correctly there is a chance of leaking the fresh charge out of the cylinder. But the actual diagram will vary with the engine design and the specification. This is the theoretical port timing diagram for the 2 stroke engine. With this action, the cycle completes within the one revolution of crank and cycle repeats again. The piston reaches the Bottom Dead centre (BDC). So this fresh charge will also push the remaining combustion particles from the cylinder. ![]() Now the fresh charge will be charged into the cylinder. Right after the opening of the exhaust port opening, the transfer port will also open within 10° angle. The combustion particles will be pushed out of the cylinder. ![]() The Exhaust port will be opened 70° before reaching to the Bottom Dead Centre (BDC). which means enough charge will be drawn into the crankcase. The Inlet Port closes after 50° from the Top Dead Centre (TDC). This is the expansion stroke due to the combustion of the air-fuel mixture due to the spark. This ‘overlap’ helps in better ‘scavenging’ or expelling the remaining exhaust gases from the engine cylinder.When the engine piston reaches the Top Dead Centre (TDC) and starts moves from the top dead centre (TDC) to bottom dead centre (BDC). At this point, both the inlet & exhaust valves remain open for a very short period of time causing an ‘overlap’. when the piston starts to move down the cylinder in the suction stroke. The exhaust valve closes after a few degrees of piston reaching the TDC, i.e. It releases the excess pressure and helps to reduce pumping losses for the piston when it moves up. ![]() As the exhaust valve opens just before BDC, it causes some of the pressurized exhaust gases to escape even before the piston starts it’s upwards stroke. The exhaust valve opens before the piston reaches BDC in its power stroke. In the exhaust stroke, the piston again moves upwards pushing the exhaust gas out through the open exhaust valve. The engineers precisely calibrate the actual closing point of the inlet valve in such a way that it coincides with the point where the motion of the incoming charge starts to reverse. At this point, the pressure in the cylinder becomes almost equal to the atmospheric pressure. Hence, the inlet valve is kept open until the piston enters its next upward stroke i.e the compression stroke. If the inlet valve closes at this point, the cylinder will receive less charge than its requirement. Therefore, the pressure in the combustion chamber remains below the atmospheric pressure, while the charge is still moving in the direction of the motion of the piston with high velocity. The entire charge cannot enter the cylinder even when the piston reaches the end of its downward stroke because the opening of the inlet valve is small. This air-fuel mixture (also known as charge) has both mass and motion. This is because the downward movement of the piston creates the vacuum (or negative pressure) in the cylinder and the air-fuel mixture gets filled in the empty space. In suction stroke, the air-fuel mixture or charge gets sucked into the cylinder very rapidly. when the piston starts to move up the cylinder in the compression stroke. Valve timing diagram of 4- stroke single cylinder diesel engine. It closes after quite a few degrees of piston reaching the BDC, i.e. 2-Stroke single cylinder petrol engine: Working: port is used instead of valve. The inlet valve usually opens few degrees before the piston reaches TDC in its exhaust stroke. Engine valve timing is the most critical process of IC engines. The timing of the opening & closing of valves is specified in degrees corresponding to the position of engine’s pistons. The engine’s camshaft opens and closes the valves at a specific interval. An automotive engine uses valves for it’s ‘breathing’ (inhale/exhale) process. The engine valves are just like the human nose. Firstly, read here about how the engine valves open & close.
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