Piston presentation

Detail presentation on "piston of IC engines"

1. SEMINAR ON PISTON OF I.C. ENIGNE Presented By Tejinderpal Singh 1508478 D4ME/B2 Department of Mechanical Engineering, Guru Nanak D ev Engineering College, Ludhiana

2. CONTENTS Introduction Piston Parts of piston Piston Functions Desirable characteristics of piston Piston head shape Piston types Piston failures Piston Materials Future piston Shape References

3. INTRODUCTION A Solid cylinder or disk that fits snugly into a hollow cylinder and moves back and forth under the pressure of a fluid{typically a hot gas formed by combustion, as in many engines}, or moves or compresses a fluid, as in a pump or compressor.

4. PARTS OF PISTON The Crown is the top surface of the piston which is subjected to tremendous forces and heat during all engine operation. The Ring Lands are the distance between the piston crown and the ring groove. Ring Groove is a recessed area located around the perimeter of the piston that is used to retain the piston ring. Skirt of a piston is the portion which is closest to the crank shaft that helps align the piston as it moves in the cylinder bore. Wrist Pin Boss is a bore that connects the small end of the connecting rod and the piston by a wrist pin.

5. PISTON FUNCTIONS To transmit the force of explosion to the crankshaft. To form a seal so that the high pressure gases in the combustion chamber do not escape into the crankcase. To serve as a guide and a bearing for small end of the connecting rod. Piston Skirt Functions Its function is to form a guide suitable for absorbing the side thrust produced on account of the inclination of the connecting rod. It must be of sufficient length to resist tilting of the piston under load. The combustion pressure from the piston crown is transmitted to the connecting rod through the ‘webs’ inside the piston. The webs also form heat path from the piston crown to the gudgeon pin bosses and the skirt. The ‘Bosses’ form a bearing surface for the rocking motion of the connecting rod.

6. DESIRABLE CHARACTERISTICS OF A PISTON It should be silent in operation. The design should be such that seizure does not occur. It should offer sufficient resistance to corrosion. It should have the shortest possible length. It should be lighter in weight. Its material should have a high thermal conductivity. It must have a long life.

7. PISTON HEAD SHAPE Flat head piston Recessed head piston Domed head piston Top of the piston is called head or crown. Some pistons head is provided valve relief. Pistons used in some high powered engines may have raised domes, which increases compression ratio as well as controls the Combustion. In some engines pistons may be specially dished to form the desired shape of the combustion chamber.

8. PISTON TYPES

9. Piston with horizontal slot Piston with Vertical slot Piston with T - slot Piston with Inclined Slot

10. OFFSET PIN TYPE PISTON Piston Description: The piston pin is offset towards the major thrust side of the piston to reduce piston wear, and piston noise. The major thrust side is the side that is loaded during the power event. The minor thrust side is the side loaded during the compression event.

11. CAM GROUND PISTON Piston Description: Most pistons are cam ground, this means they are not perfectly round. The diameter is larger on the non-thrust sides, because they tend to expand more as the temperature of the piston increases .

12. OIL COOLED PISTON Piston Description : A cavity is provided underneath the piston crown. To reduce the piston temperatures at the top ring to prevent carbon formation in the groove and to achieve sufficient oil film thickness on the ring periphery. This type of piston is provided in the medium and heavy speed diesel engines.

13. Taper Piston (a) cold ; (b) hot TAPER PISTON Piston Description: The crown side being smaller in diameter than the skirt end . As higher temperature occurs towards the crown, that side expands more than the skirt, due to which the piston diameter becomes uniform under running conditions.

14. Steel wire wound piston Aconoguide Piston Piston Description: A Band of steel wire under initial tension is put between the piston pin and the oil ring, thus restricting the expansion of skirt which is of spilt type or cam ground type. Piston Description: This type of piston consists of raised pads which are specially shaped to assist the creation of hydrodynamic lubrication. By this method up to 75% skirt contact area is reduced.

15. Piston with Heat Dam Piston Description: A groove cut near the top of the piston. This reduces the path of heat travel from the piston crown to the skirt. The skirt, therefore, runs cooler and does not expand much. Autothermic Piston Piston Description: P iston contains low expan- sion steel inserts at piston pin boses. At higher temperatures, this arrangement causing the piston to expand along the piston pin. In the direction perpendicular to piston pin there is corresponding contraction of the piston due to metallic action.

16. BI-METAL PISTON Piston Description : Made from both steel and aluminium. Skirt is formed by the steel and the aluminium alloy cast inside it forms piston head and piston pin bosses. As the coefficient of thermal expansion for steel is quite small, the piston will not expand much and hence smaller cold clearances can be maintained .

17. PISTON FAILURE

18. Piston Scuffing Burnt Piston Damage Description: D ue to excessive heat, the piston expands and becomes tight in the cylinder. As, a result the lubricant is squeezed out from the cylinder walls causing metal to metal contact. Damage Description: This may be chiefly on account of detonation or preignition. The burning due to detonation is generally at a farthest from the spark plug where the hot end gases rapidly releases their energy. In case of preignition, however, the burning is usually near the center of the piston head.

19. PISTON DRY RUNNING Damage Description: Unburned fuel has condensed at the cylinder running surface and diluted or washed off the load-bearing oil film. As a result, the interacting sliding parts (piston and cylinder bore) run dry against each other, which results in long, narrow friction marks. The piston ring zone usually remains undamaged .

20. PISTON PIN BOSS DAMAGE Damage Description: Boss fatigue fractures arise as a consequence of mechanical overstressing. If there is no sufficient oil supply: an incipient crack in the piston pin boss will then spread even under normal loads, and will cause the piston to split.

21. PISTON MATERIAL MELT OUT Damage Description: It occurs due to glow ignition on pistons. Glow ignition is triggered by glowing parts in the combustion chamber that are hotter than the self-ignition temperature of the air-gas mixture. These are essentially the spark plug, the exhaust valves and any oil carbon deposits on the combustion chamber walls. In the quenching area, the piston head is heated up significantly due to the glow ignition.

22. PISTON FAILURE DUE TO CIRCLIP DAMAGE Damage Description : End of the piston pin bore on both sides of the piston suffered serious damage. Circlip jumped out of the retaining groove and broke into fragments. Second circlip damaged. Due to the lack of retention. Front face of the piston pin worn to a convex shape. Asymmetrical running pattern of the piston. Asymmetrical piston wear pattern Piston pin boss and piston pin broken Pin bore hammered out in the area of the circlips .

23. PISTON MATERIALS Cast iron pistons High strength. Good wearing characteristics. Low thermal expensions. Heavier then aluminium pistons. Low thermal conductivity. Aluminium - cast pistons Si-9to12%, Ni-1%. Cu-1%,Mg-1%etc. Light weight. Economical. General usage. Brittle .

24. PISTON MATERIAL Hypereutectic Si-18to24%, Ni-1%. Cu-1%,Mg-1%etc . Cast Aluminium with a high Silicon Content. 25%,Lighter weight then normal cast aluminium piston. High performance. Less Brittle. More Scuffing resistance. Expensive then cast pistons. Aluminium –Forged piston: Si-9to12%, Ni-1%. Cu-1%,Mg-1%etc . Lighter in weight than normal cast piton. Stronger then normal cast piston. Due to less porosity they can conduct heat more rapidly. Approximately runs 20% cooler then cast piston .

25. FUTURE PISTON SHAPE Piston with reduced skirt length Piston Description: Reduced Skirt length. Reduction in Friction. Reduction in Weight. Effective Lubrication. Less Heat transfer from crown to the skirt.

26. REFERENCES A text book of Automobile Engineering, Vol. 2, Dr. Kirpal Singh, Standard Publishers Distributers, Delhi, 2011. Piston Damage – recognizing and rectifying, Motor Service, Kolbenschmidt. Presentation on Piston and Piston rings, Slideshare.com Piston Evolution, Engine Technology International.com, March 2015. Pdf file of The aluminium automotive manual.