PISTONS CONCAVED OR CONVEXED AT THE TOP AND NOT FLAT WHY?

WHY THESE?

WHY NOT THIS?

PISTONS AS ASPIRING MARINERS THINK IS NOT FLAT AND IS EITHER CONCAVED OR CONVEXED.THERE ARE VARIOUS REASONS FOR THIS QUERY.

PISTONS WITH FLAT SURFACES ARE NOT SELF SUPPORTIVE AND IS SUBJECTED TO PRESSURE ON ONE SIDE AS IT OCCURS WHEN AN ENGINE PISTON IS LOADED.

AN UNSUPPORTED FLAT SURFACE TAKES CONCAVE FORM ON ONE SIDE WHICH IS LOADED AND AS LOAD OR THE GAS PRESSURE INCREASES CURVATURE OF THE CONCAVITY INCREASES DEPENDING ON THE PRESSURE APPLIED.

THUS IF PISTONS WERE FLAT THEN IT WOULD GO THROUGH A PATTERN OF CONCAVITY WHICH IS DIRECTLY PROPORTIONAL TO PRESSURE i.e IF PRESSURE INCREASES THEN THE CONCAVITY ALSO INCREASES AND VICE VERSA. THIS CAUSES THE PISTON TO SUFFER FROM FATIGUE AND FAILURE OCCURS DUE TO THE ABOVE REASON EVEN THOUGH THE PARTS OF THE PISTON ARE GOOD.

CURVED SURFACES ARE SELF SUPPORTING WHEN LOADED ON ONE SIDE. THEY DON'T CHANGE THEIR SHAPE OR MOVE TO ANY DEGREE WITH CHANGES IN PRESSURE. HENCE FATIGUE FAILURE IS REDUCED AND IF THEY ARE RIGHTLY ARRANGED IN CONJUNCTION WITH THE FUEL INJECTOR GOOD COMBUSTION OCCURS.

SOME LARGE, SLOW SPEED, HIGHLY RATED 2 STROKE ENGINES HAVE CONVEX STRUCTURE ON OUTER PERIPHERY.THIS IS CLOSED BY A FAIRLY EXTERNAL FLAT AREA SUPPORTED BY BRACKETS ASSISTING IN COOLING AND REDUCING COMPRESSION LOAD ON THE PISTON WALLS.

SOME OTHER SECONDARY REASONS ARE THAT THE GAS PRESSURE DURING THE EXHAUST CAN BE EASILY REMOVED THROUGH THE PORTS IN CASE OF LOOP AND CROSS SCAVENGED ENGINES AND SOMETIMES ON THE SIDES THEY ARE HELPFUL FOR THE OPENIG AND CLOSING OF THE EXHAUST AND INLET VALVES.