11/19/2023 0 Comments Valve and ignition timing diagram![]() A four stroke engine may also have a blower. On the two-stroke cycle engine, the system also includes a blower for scavenging air and for combustion.On a naturally aspirated four-stroke-cycle engine, the system includes the air cleaner, a precleaner (if used), the intake manifold, and the connecting tubing and pipes.INDUCTION - The induction system provides the engine with an adequate supply of clean air for good combustion (and for scavenging cylinders on two and four stroke-cycle engines) for all operating speeds, loads, and operating conditions.ĬOMPONENTS WHICH ARE LIKELY TO BE FITTED IN AN INDUCTION SYSTEM Let it be 4 stroke engine or 2 stroke engine, both of hem have to undergo these 5 cycles. INDUCTION, COMPRESSION, IGNITION, EXPANSION and EXHAUST. Universally all the engines have 5 cycles i.e. So what all timing cycles are we looking at? As a result it becomes very important for us to understand as to what is happening when inside an engine cylinder so that we can troubleshoot accordingly. If we are not experiencing ignition of fuel at a position of piston where it normally occurs than we are likely to experience unfavorable combustion and poor engine performance. If all these strokes don't happen at the prescribed/designed time and instance than the engine will not work as it should. Exhaust valve lead helps to increase overall efficiency by decreasing the work done required to forcing out the burned gas.Now that we have learnt about engine classification let's now try and understand Engine Timing and associated Terminology.Įngine timing is the determination of what happens when inside an engine cylinder i.e at what position and at what instance we have Induction, Compression, Ignition and Exhaust.Intake valve lag helps to intake more air/fresh charge by the help of inertia effect of flowing air/ air-fuel mixture.Overlap is a secondary means of cooling of exhaust valve by fresh intake.Valve overlap/exhaust valve lag helps to scavenging of burned gas at region clearance volume.Valve overlap/ intake valve lead ensure the complete opening of intake valve when piston reached at TDC (and begins the intake stroke) so that it can suck large amount of air, fresh charge during suction stroke.Need or Advantages of valve lead, valve lag and overlap ![]() The overlap should not excessive so that it causes the expelling of fresh charge through the exhaust valve, or sucking of burned gas into the cylinder. The valve overlapping is a secondary means of cooling the exhaust valve by fresh air intake during the overlap. Ie the period of inlet valve lead and period of exhaust valve lag referred as overlap. The intake valve opens before piston reaches the TDC and exhaust didn’t close until piston passes the TDC. It happened at the end of exhaust stroke and at the beginning of intake. Valve overlap in valve timing diagramValve overlap is the short period of time in which both the inlet and the exhaust valve is open. ![]() □ Variable valve timing VVT of internal combustion engine - Advantages Valve lag – Inlet valve close after piston passed the BDC (at beginning of compression stroke), the exhaust close after piston passed TDC (at the beginning of suction stroke). But in a real engine, the inlet valve is set to close some degree (time) after the piston reaches the BDC and exhaust valve close after piston passed the TDC. Valve lag in valve timingIn the case of closing of the valve, in theoretical valve timing, the inlet valve close when the piston reaches the BDC and exhaust valve close when piston reaches the TDC. Both situations are described as valve lead. Valve lead - Inlet open before piston reach TDC (at the end of exhaust stroke), Exhaust open before piston reach BDC (at the end of power stroke). Theoretically the inlet valve open at TDC and exhaust valve open at BDC, but in engine design, it is set to that the inlet valve open before the piston reaches the top dead center, and exhaust valve open before the piston reaches the bottom dead center. The term “lead” and “lag” used to represent where the actual opening and closing of valve occurred. However, in a practical situation, opening and closing of engine valve occur at some degree (time) before or after TDC and BDC. Valve lead in engineTheoretically, the engine valve opens and closes at TDC (Top Dead center) and BDC (Bottom Dead Centre). ![]()
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