14-10-2016, 02:44 PM
1459052908-newDESIGNANDFABRICATIONOFPENTROOFCOMBUSTIONCHAMBER.pptx (Size: 95.07 KB / Downloads: 5)
OBJECTIVE
To design a modified pent-roof combustion chamber.
To perform thermal analysis and structural analysis on the piston.
To fabricate the pent-roof piston.
INTRODUCTION
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In a pump, the function is reversed and force is transferred from the crankshaft to the piston for the purpose of compressing or ejecting the fluid in the cylinder. In some engines, the piston also acts as a valve by covering and uncovering ports in the cylinder wall.
Slipper piston:
A slipper piston is a piston for a petrol engine that has been reduced in size and weight as much as possible. In the extreme case, they are reduced to the piston crown, support for the piston rings, and just enough of the piston skirt remaining to leave two lands so as to stop the piston rocking in the bore. The sides of the piston skirt around the gudgeon pin are reduced away from the cylinder wall.
Trunk pistons:
Trunk pistons are long relative to their diameter. They act both as a piston and cylindrical crosshead. As the connecting rod is angled for much of its rotation, there is also a side force that reacts along the side of the piston against the cylinder wall. A longer piston helps to support this.
Crosshead pistons:
Large slow-speed Diesel engines may require additional support for the side forces on the piston. These engines typically use crosshead pistons. The main piston has a large piston rod extending downwards from the piston to what is effectively a second smaller-diameter piston. The main piston is responsible for gas sealing and carries the piston rings. The smaller piston is purely a mechanical guide. It runs within a small cylinder as a trunk guide and also carries the gudgeon pin.
Deflector piston:
Deflector pistons are used in two-stroke engines with crankcase compression, where the gas flow within the cylinder must be carefully directed in order to provide efficient scavenging. With cross scavenging, the transfer (inlet to the cylinder) and exhaust ports are on directly facing sides of the cylinder wall. To prevent the incoming mixture passing straight across from one port to the other, the piston has a raised rib on its crown. This is intended to deflect the incoming mixture upwards, around the combustion chamber.
Literature survey
The pent roof combustion chamber was reputedly used first in the engine of the 1904 Welch Model 4.0 built by The Welch Motor Co., Pontiac, Mi.
Pent roof combustion chambers were also used by Chrysler between 1951 and 1958 when it was discontinued due to high costs.
Nowadays almost all IC engines have some variation of a pent roof combustion chamber. This produces a high volumetric efficiency having at least two exhaust and two inlet valves/cylinder, driven by a single OHC or double OHC. The pent roof combustion chamber also reduces exhaust emissions, but although a high flame speed induces more power, this can also produce excessive levels of NOx’s.
Papers presented under pent-roof combustion chamber:
METHODOLOGY
Firstly dimensions are taken for designing the piston.
After designing the piston ,structural analysis and thermal analysis of the piston is analyzed.
Thirdly fabrication of the piston is done .
Material used is aluminium alloy because of its light weight, corrosion resistance and it is also easy to machine, it has high strength to weight ratio and finally it is recyclable cost efficient.