Modelling and analysis of lubricated piston skirt-cylinder sub-systems in internal combustion engines
Amirun Rasyid Abu Bakar
Date of Issue2017-05-26
School of Mechanical and Aerospace Engineering
This paper aims to investigate the efficiencies of the 4-stroke engine by observing the lubrication present in the piston skirt-cylinder assembly. The main investigation is done on the translational joint connecting the piston skirt to the piston liner. Simulation is run using Visual Studio with FORTRAN compiler using Finite Element Method and Reynolds Equation. Parameters that are varied in the code are piston skirt-liner clearance, lubricant dynamic viscosities and crank velocities. Dynamic viscosities of 0.01Pas – 0.04Pas was considered as they overlapped with the engine oils available are tested. The crank velocities of 1000, 2000, 4000 and 6000 rpm are used to simulate mean operating crank shaft velocities. The clearances tested are 0.015, 0.025, 0.035, 0.045 and 0.055mm. The results are as expected with the higher RPM and viscosities generating the highest frictional power losses (FPL). However, the trend isn’t linear, as it is found that low RPM operating with lubricants of higher viscosities can also generate high FPL and thus, a case study is done to analyse and apply the findings. The different dynamic viscosities of SAE rated engine oils are investigated to be used for our case study. The cars chosen in the case study are the Honda Civic 2012 models with different engine capacity. Results obtained from the simulations are applied to the estimated modal operating crank velocity and analysed. It is also found that the higher clearances will incur higher secondary motion and velocities of the piston. And as a result, there will be a higher amount of vibrations and noise as a consequence. A careful balance of these variables is needed to ensure the highest efficiency of the piston skirt-liner lubrication. As such, a with a good knowledge of all three variables together, which are modal operating crank velocities of the vehicle, dynamic viscosities of the lubricant and the clearance specifications of the car engine, will allow car owners to maximise the efficiency and performance of their machine.
Final Year Project (FYP)
Nanyang Technological University