What is a Piston Ring, and how does it work?

Types of Piston Rings and Their Functions What is a Piston Ring, and how does it work?

Types Of Piston Rings And Their Functions:- In an IC engine, piston rings are metallic split type rings that are inserted into the grooves of the piston's outer diameter to maintain a good deal between piston and cylinder wall. In an IC engine, 3 to 4 rings are often employed.

Piston Rings' Purpose   

It acts as a pressure seal for burned gases, preventing them from entering the crankcase.

They serve as a conduit for heat transfer from the piston crown to the cylinder walls.

They keep the flow of oil to the skirt under control and prevent it from mingling with the gases within the combustion chamber.

Types of Piston Rings There are two types of piston rings; 1. Rings of Compression a) Counter bored and scrapper rings b) Headland rings 2. Oil control Rings

1. Compression Rings The piston usually has two or three compression rings installed. The compression ratio determines the number of compression rings.

Generally 2nd and 3rd compression rings are usually taper-faced. These are used to solve ringsticking issues in high-performance engines.

Oil control rings often contain a series of slots that carry surplus oil via holes in the piston groove to the interior of the piston and to sumps while leaving enough oil for cylinder wall lubrication.

Compression rings provide somewhat greater radial pressure to the cylinder walls than oil rings.

A) Scrapper and Counter Bored Rings For top and second compression rings, counter bored and scrapper rings are often employed.

Internal pressures caused by cutting away corner rings cause these rings to rotate slightly during the suction stroke.

When the piston rises higher during the compression stroke, the rings move upward as well, and they tend to push on the oil coating within the cylinder wall. As a result, the volume of oil fed to the combustion chamber is reduced.

During the power stroke, the pressure from combustion leads the rings to untwist, allowing them to make full contact with the cylinder walls for good sealing.

(B) Headland Rings Headland rings are a kind of compression ring that is unique. They feature a cross section that is formed like an L. It protects the region around Piston's headland. There is some unburned air fuel combination in this location.

This unburned combination may cause haze after cooling. This may be prevented by using headland rings, and the unburned mixture can be exhausted. During the power stroke, these rings offer effective sealing. It has a 10% boost in horse power.

The headland rings have the added benefit of providing strong sealing during the power stroke.

When combustion begins, the pressure works immediately on the ring's top lip, driving it out and ensuring effective sealing with the cylinder wall.

2. Oil Control Rings During each revolution of certain IC engines, the inner connecting rod divides oil from the oil pan. As a consequence, more oil reaches the cylinder wall than is required. It has to be scraped off and placed back in the oil pan. Otherwise, it will be sent to the combustion chamber and will be burned. As a result, oil consumption will rise, and the engine will need more regular oil changes. Oil removal from within cylinder walls is just as critical as cooling, sealing, and cleaning.

There are three different kinds of oil rings.

(i). One-piece slotted cast iron type: the cylinder features slots on both the top and lower sides.

To boost scrapping action, the expander spring raises the pressure of the ring on the cylinder wall. (ii). One-piece pressed steel type: These are often utilized in worn engine cylinder walls. Steel is used to construct it. It has the ability to seal one side of the groove. (iii). Three-piece steel rail with expander: enables sealing in both upward and downward directions. As a result, they are more effective at sealing.

Material Used For Piston Rings Fine-grained alloy cast iron is the most typical material for piston rings. Because graphite is contained in cast iron, it has a self-lubricating feature that reduces friction in cylinder liners and rings.

For optimal longevity, the piston ring material should be tougher than the cylinder lining.

Nickel, chromium, titanium, copper, vanadium, and molybdenum are common alloys used in cast iron. Piston rings are also made of pressed steel.

1. Piston Ring Gap Piston rings have a space between them and the piston grooves so that they may be fitted and withdrawn from the grooves as they wear out. Under strong pressure, the radial pressure produced by the gap guarantees efficient sealing to avoid leakage.

The spacing offered should be optimal, which means it should not be too little or too large. The spacing ranges from 0.178 to 0.50mm, and if the piston is greater than this, the gap is raised by 1mm for every 100mm increase in diameter.

For compression rings, the distance between the ring and the grooves should be between 0.038 and 0.102mm, and a bit less for oil control rings. During service, the ring may have lost part of its elastic qualities, resulting in a reduction in radial pressure on the cylinder wall. The spacing between fresh and old rings may be compared to see whether they're the same.

2. Ring Coating Piston rings are exposed to high temperatures and frequent loading situations, therefore they wear out quickly. As a result, different coatings are applied to the compression rings.

Rings are often coated with relatively soft materials such as phosphate, graphite, and iron oxide.

Oil-absorbent ring coatings are also available. They absorb oil quickly and increase ring lubrication as a result. They also keep rings from scuffing. Metal to metal contact at high temperatures causes scuffing. It's a phenomena similar to welding. Because the coating inhibits scuffing, no weld can be made because there is no exposed iron.

By chromium playing the ring rather than the bore, the rate of wear in the cylinder bore may be significantly decreased.