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Title: Integrated investigation of piston-cylinder impact-induced noise and passive control of the piston's secondary motion using nonlinear absorbers
Author: Dolatabadi, Nader
ISNI:       0000 0004 7971 0661
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2016
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Although alternative power sources are getting well-established, transportation will remain primarily dependent on IC engines using fossil fuels for at least a few more decades. The IC engines typically employ reciprocating pistons to convert the combustion pressure into mechanical work required by the vehicle. Engine NVH issues make their appearance at the piston-cylinder interface in the form of impulsive vibration signals. The piezo-viscous nature of the lubricant at the piston-cylinder conjunction can change the dynamic response of the impacting structures. Much of the published research to date has excluded the elasto-hydrodynamic effects of the lubricant on piston impact noise. Even when these effects were studied, the research focus has been primarily on the tribology of the contact. Thus, an accurate methodology is required to identify and predict piston impact noise using real in-cylinder conditions, especially at the lubricated piston-cylinder conjunction. This thesis presents a methodology to identify and predict piston impact noise for lubricated piston-cylinder conjunctions based on a multi-physics, multi-scale approach. The piston's kinematics and dynamics are determined in macro scale. The model of piezo-viscous lubricant film is developed in micro scale. The transferred impact power to the cylinder liner is evaluated through the elasto-hydrodynamic lubricant film. The radiated power from the engine surface integrates dynamics, tribology and acoustics. The model created has been verified against surface vibration and acoustic measurements in the laboratory using a single cylinder engine. One of the key findings is that identification of piston impacts is more accurate through methods developed for lubricated conditions. In the second part of the thesis, the feasibility of nonlinear energy absorbers to passively control the undesirable piston secondary motion is explored. The broadband operational frequency of the nonlinear absorbers shows the potential for reduction of the impact excitations. The examined absorber designs are single pendulum and double pendula oscillators with nonlinear stiffness and linear damping. The key finding is that the application of nonlinear energy absorbers can reduce the number and severity of impacts through controlling piston's secondary motion. The potential of this concept should be explored experimentally in the future in terms of the actual piston impact noise improvement, as well as the associated effects in power loss.
Supervisor: Not available Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Mechanical Engineering not elsewhere classified ; Transient elasto-hydrodynamic lubrication ; Piston impacts ; Slap noise ; Structural vibration energy ; Targeted energy transfer ; Nonlinear energy sink