A Simulation Tool for Optimising Combustion Engine Cylinder Liner Surface Texture

Abstract: Fuel efficiency is one of the most important areas of automotive vehicle research and development today, with rising fuel costs, energy security and environmental concerns being at the forefront of customers and legislators minds. Heavy Duty Diesel Engines (HDDE) are the primary source of mechanical power generation in today’s trucks and buses and this is likely to continue for the foreseeable future. In the 2011 European Commission White Paper on transport, a reduction of at least 60% of greenhouse gas emissions from transport by 2050, with respect to 1990 levels, was called for. The report concludes that acting on vehicles’ efficiency through new engines, materials and design will help in the reduction of oil dependence, the competitiveness of Europe’s automotive industry as well as health benefits, especially improved air quality in cities. Therefore, the efficiency and frictional losses in a vehicles powertrain are areas of great interest. This thesis focuses on the Piston Ring to Cylinder Liner (PRCL) contact and the potential for improving its performance through the specification of an optimised cylinder liner surface texture. The PRCL contact is one of the biggest contributors to mechanical losses in a HDDE and so there is potential for large performance gains to be achieved through optimisation of this contact. This research has led to the development of a simulation tool capable of calculating the friction, lubrication regime, oil consumption risk and wear that occurs in the full ring-pack of a HDDE. Furthermore, the tool allows for the evaluation of the relative performance of different cylinder liner surface topographies. A mixed lubrication model, incorporating flow factors calculated using the homogenization technique, has been implemented to allow all regimes of lubrication to be considered. A mass-conserving cavitation algorithm, formulated as a Linear Complimentarity Problem, enables lubricant cavitation, fully-flooded or starved inlet conditions and the quantity of lubricant deposited on the cylinder liner surface to be modelled. The simulation tool is validated with both reciprocating bench tests and full single cylinder fired engine tests. The reciprocating bench tests measured both friction and film thickness and both showed good correlation with the predictions from the simulation tool. Simulations and experiments were conducted on four different cylinder liner variants and both ranked the frictional performance of the cylinder liner variants in the same order. A parametric study of honing depth, spacing and angle was undertaken using the developed simulation tool and the influence of these parameters on lubricant film thickness, friction, wear and oil consumption was investigated. The thesis concludes that a reduction in specific fuel consumption is achieveable through the optimisation of cylinder liner texture and outlines how this might be achieved.