MEO FUNCTION IV

Draw the valve timing diagram of 4 Stroke naturally aspirated and supercharged engine and why overlap period is more in pressure charged engine?

Differences of the timing of the air inlet and exhaust valves differ between naturally aspirated and pressure charged four stroke engines. These differences depend to some extent on the speed of the engine and also on the degree of supercharging.

stroke

FIG: VALVE TIMING DIAGRAM FOR NATURALLY ASPIRATED ENGINE 4-STROKE ENGINE

stroke 1

FIG: VALVE TIMING DIAGRAM FOR NATURALLY TURBOCHARGEDED ENGINE 4-STROKE ENGINE

What is overlap period?

The overlap period is when both the exhaust and air inlet valves are opened together. It is sometimes referred to as the scavenge period in pressure charged four stroke engines.

Overlap period in naturally aspirated and supercharged engine:

 In the naturally aspirated engine, the overlap is 36°; in the pressure charged engine, it is 120°

Advantage of large overlap period:

The large overlap period in the pressure charged engine allows complete expulsion of exhaust gases from the cylinder. During this period, a large amount of air passes through the inlet valve, cylinder, exhaust valve and cooling the parts in the process. This cooling helps to keep the surface temperatures of these parts at a lower value, which reduces thermal stresses.

After the exhaust valve closes, less heat is passed into the air that follows into the cylinder and a greater mass of air is therefore present when compression begins.

About the author

Anand Gautam

Anand Gautam is a marine engineer, Graduated from M.E.R.I. Mumbai. He likes to sail onboard ship and is one who is passionate about his job. He loves to share his knowledge, information, and ideas to everyone in a simplified way just for his satisfaction.

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