1,489 research outputs found
Tribology of piston compression ring conjunction under transient thermal mixed regime of lubrication
Fuel efficiency is the main IC engine attribute, with the compression ring-bore contact consuming nearly 5% of the fuel energy. Analyses are often idealised, such as isothermal condition and smooth surfaces, the former being particularly contrary to practice. An analytic solution to the average flow model is presented for this contact with a new analytical thermal model. The generated contact temperatures, particularly at the inlet result in thinner films than the idealised analyses. For the simulated city driving condition the power loss is mainly due to viscous shear under cold engine condition, whilst for a hot engine boundary friction dominates
Mathematics of moving boundary problems in diffusion
This thesis is concerned with the development, generahzation and apphcation of a formal series technique for classical one-dimensional moving boundary diffusion problems. The solution procedure consists of two major steps. Firstly, the introduction of a boundary fixing transformation, which fixes the moving boundary and simplifies the transformed equations. Secondly, the assumption of a formal series solution which leads to a system of ordinary differential equations for the unknown coefficients in the series. The method generalizes to multi-phase and heterogeneous moving boundary problems for both constant temperature and Newton\u27s radiation conditions and yields simple and highly accurate estimates for both the temperature and boundary motion
Super-hydrodynamic limit in interacting particle systems
This paper is a follow-up of the work initiated in [3], where it has been
investigated the hydrodynamic limit of symmetric independent random walkers
with birth at the origin and death at the rightmost occupied site. Here we
obtain two further results: first we characterize the stationary states on the
hydrodynamic time scale and show that they are given by a family of linear
macroscopic profiles whose parameters are determined by the current reservoirs
and the system mass. Then we prove the existence of a super-hyrdrodynamic time
scale, beyond the hydrodynamic one. On this larger time scale the system mass
fluctuates and correspondingly the macroscopic profile of the system randomly
moves within the family of linear profiles, with the randomness of a Brownian
motion.Comment: 22 page
Computation of entropy generation in dissipative transient natural convective viscoelastic flow
Entropy generation is an important aspect of modern thermal polymer processing optimization. Many polymers exhibit strongly non-Newtonian effects and dissipation effects in thermal processing. Motivated by these aspects in this article a numerical analysis of the entropy generation with viscous dissipation effect in an unsteady flow of viscoelastic fluid from a vertical cylinder is presented. The Reiner-Rivlin physical model of grade two (second grade fluid) is employed which can envisage normal stress variations in polymeric flow-fields. Viscosity variation is included. The obtained governing equations are resolved using implicit finite difference method of Crank-Nicolson type with well imposed initial and boundary conditions. Key control parameters are the second-grade viscoelastic fluid parameter (β), viscosity variation parameter (γ) and viscous dissipation parameter (ε). Also, group parameter (BrΩ-1), Grashof number (Gr) and Prandtl number (Pr) are examined. Numerical solutions are presented for steady-state flow variables, temperature, time histories of friction, wall heat transfer rate, entropy and Bejan curves for distinct values of control parameters. The results specify that entropy generation decreases with augmenting values of β, γ and Gr. The converse trend is noticed with increasing Pr and BrΩ-1. Furthermore, the computations reveal that entropy and Bejan lines only occur close to the hot cylinder wall
A Moving-Mesh Finite Element Method and its Application to the Numerical Solution of Phase-Change Problems
A distributed Lagrangian moving-mesh finite element method is applied to problems involving changes of phase. The algorithm uses a distributed conservation principle to determine nodal mesh velocities, which are then used to move the nodes. The nodal values are obtained from an ALE (Arbitrary Lagrangian-Eulerian) equation, which represents a generalisation of the original algorithm presented in Applied Numerical Mathematics, 54:450–469 (2005). Having described the details of the generalised algorithm it is validated on two test cases from the original paper and is then applied to one-phase and, for the first time, twophase Stefan problems in one and two space dimensions, paying particular attention to the implementation of the interface boundary conditions. Results are presented to demonstrate the accuracy and the effectiveness of the method, including comparisons against analytical solutions where available.
Transient elastohydrodynamic analysis of piston skirt lubricated contact under combined axial, lateral and tilting motion
Most modern engines utilise pistons with an offset gudgeon pin. In internal combustion
engines, the offset is to the major thrust side of the piston. The piston thrust side is the
part of the piston perpendicular to the gudgeon pin that carries the majority of side
loading during the power stroke. Primary reason for having the gudgeon pin positioned
eccentrically is to prevent the piston from slamming into the cylinder bore after the
connecting rod journal passes the top dead centre. This phenomenon is referred to as
piston slap, and is more pronounced in compression ignition and high performance
engines due to higher combustion pressure than that of commercial spark ignition
engines. The coming together of the piston and the bore results in scuffing, at best, or,
catastrophic failure at worst. Clearance space between bore and piston is filled by a
lubricant film. The main role of the lubricant is to separate the piston and bore by
reacting to the applied load.
Investigating the above problem requires a holistic approach, whereby a dynamic three
degree-of-freedom piston model is coupled with a lubrication model to represent the
actual system. The dynamic model determines the motion of the piston in combined
axial, lateral and rotation about the gudgeon pin. The reactive forces due to lubricant
films on the major and minor thrust sides of the piston play significant roles in piston
dynamics and are evaluated by either quasi-static or transient solution of the lubricant
contact conjunctions.
The novel quasi-static analysis is carried out in the sense of its detailed approach,
including many key practical features. not incorporated in other analyses, hitherto
reported in literature. These features include first and foremost the development of a
specific contact mechanics model for evaluation of conforming contacts for piston skirt
against liner or bore. The quasi-static analysis includes many practical feature not
encountered in other literature on the subject, such as detailed surface irregularities and
modification features, and with thermal distortion. The analysis has been extended to
thermohydrodynamics, as well as micro-hydrodynamics, all with high computational
mesh densities, and robust methods of solution in space and time domains, including
effective influence Newton-Raphson method and linear acceleration integration scheme.
The transient tribo-elasto-multi-body dynamics problem includes physics of motion study
from film thickness prediction and secondary motion evaluation of the order of
micrometers and minutes of arc to large rigid body dynamics, including simultaneous
solution of the contact problem at both major and minor thrust sides. Such a
comprehensive solution has not hitherto been reported in literature.
The thesis discusses many aspects of piston dynamics problem, through the broad
spectrum of vehicle manufacture, with many pertinent practical engineering issues. In
particular, it provides solutions for high performance Formula 1 racing engines. This is
the first ever comprehensive analysis of piston tribodynamics for this range of engines at
very high combustion pressures.
This study has shown the paramount influence of profile of piston in promoting
lubrication between the contiguous bodies, as evident from the pattern of lubricant flow
through the contact. Deformation of the bodies increases the volume of lubricant in the
contact. During the reversal in direction of piston motion, when the entraining velocity
momentarily cases and reversal takes place, the load is held by an elastic squeez
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