الفهرس 
صفحة العنوانOnly 14 pages are availabe for public view
 |  | from | 193 |  |  |
| | | from | 193 | | |
Abstract
The latest developments in the engine’s design aim to maximize the power output, downsize the engine, minimize the fuel consumption, and to be pollution-free as possible. The piston assembly is considered the heart of the engine and its working conditions are the worst one where a high amount of heat and pressure is developed.
This thesis investigates the thermo-mechanical loads of the combustion gases and dynamic inertia on the piston assembly of a turbocharged diesel engine. The main emphasis is the effect of increasing the boosting pressure on the piston assembly loading until the possible maximum engine power is achievedand suggests the modification of the piston assembly design in order to increase the durability for more power loading and decrease the total mass. The temperature distribution, thermo-mechanical deformations, axial stresses (compressive/tensile) distribution, and safety factors on the piston assembly body are excessively calculated in order to predict any failure. Finite element methods (ANSYS-workbench) is used to analyze the thermal and mechanical loads applied to a three-dimensional model. The study is applied to the piston assembly of a 300 hp diesel engine (the base case) in order to increase the engine power by 17%, to be 350 hp (the upgraded case).
The piston, piston rings, piston pin, and connecting rod remain within safe conditions and can withstand further loads until the extra power increase reaches 56.7%. In order to withstand more loads with lower mass, the piston under consideration may be modified in several methods. First, opening an oil cooling channel inside the piston crown. Second, decreasing the thickness and length of the piston skirt and pin bosses. Finally, increasing the diameter of the piston pinhole and the fillet radius around pin bosses. Analytical investigations show that these modifications would reduce the maximum temperature, deformation at the piston crown, and the total mass of the piston by 32.4%, 39.4%, and 15.8%, respectively with no increase in the stresses. Further that, the piston pin is modified by decreasing its length from the low stressed regions at the edges. This modification leads to reduce the pin mass by 9.1%. Moreover, the connecting rod most stressed points are at the shank while less stressed are experienced at the big end. Calculations show that introducing minor changes to the rod geometry may result in decreasing the stresses. These changes include increasing the thickness of the shank cross-section, increasing the fillets radii and slightly decreasing the dimensions of the big end in order to maintain the same mass. The new geometry could significantly reduce the maximum stress by 25.5% with an insignificant reduction in the total mass of the connecting rod.
The modified piston assembly design can withstand, safely, the loads when the engine power increasesby up to 90%,more than the basic design by 33.3% with a lower mass by 6.6%.