A Review of Surface Texturing in Internal Combustion Engine Piston Assembly

This paper presents a brief review of surface texturing with a focus on piston assembly application. The paper begins with a general discussion on surface texturing and the manufacturing process of micro dimples.  Further, it discusses the theory of hydrodynamic lift generation and the effect of parameters of micro dimples texture on the surface-to-surface friction. Finally, the effect of surface texturing on heat transfer is briefly discussed. In pursuits to improve internal combustion engine (ICE) efficiency, tribological improvement of moving surfaces by means of micro surface texturing seems to be one of the way. However, texturing parameters have to be carefully designed as it can cause detrimental effect if the designs are wrong. Studies has shown micro surface texturing at piston ring could reduce friction around 20%-50% compare with un-textured piston ring and also reduce fuel consumption at 4%. Micro Surface texturing could also improve heat transfer between the surfaces to reduce piston slap and lubrication oil temperature. As reports on the surface texturing on friction reduction and heat transfer improvement in piston assembly are relatively scarce, it is suggested that optimization of micro dimple parameters for piston skirt application and its effect on engine tribology and heat transfer characteristics be further investigated

An investigation on design and analysis of micro-structured surfaces with application to friction reduction

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityDrag reduction in wall-bounded flows can be achieved by the passive flow control technique using riblets and surface grooves aligned in the mean direction of an overlying turbulent flow. They were inspired by the skin of fast sharks covered with small longitudinal ribs on their skin surfaces. Although it was found that the drag reduction depends on the riblets’ geometrical characteristics, their physical mechanisms have not yet been fully understood in the scientific terms. Regarding riblets sizing, it has been critically explained in the literature how riblets with vanishing size interact with the turbulent flow and produce a change in the drag proportional to their size. Their shapes are focused upon because these are most significant from a technological perspective, and also less well understood. Different riblet shapes have been designed, some with complicated geometries, but except for the simple ones, such as U and V grooves, there has not been enough study regarding shape features. Therefore, special effort is undertaken to the design of an innovative type of ribleted surface, e.g. the Serrate-Semi-Circular shape, and its effect on the skin friction and drag reduction. In this work, the possible physical mechanisms of riblets for turbulent drag reduction have been explored. The modelling and experiments concerning the relationship between the riblets features and the turbulent boundary layer structure have also been reviewed. Moreover, numerical simulations on riblets with different shapes and sizes are presented and studied in detail. An accurate treatment based on k-ε turbulence model was adopted to investigate the flow alteration and the consequent drag reduction on ribleted surfaces. The interaction of the overlying turbulent flow with riblets and its impact on their drag reduction properties are further investigated. In addition, the experimental facilities, instrumentation (e.g. hotwires) and measurement techniques (e.g. time-averaged turbulence structure) have been employed to experimentally investigate the boundary layer velocity profiles and skin friction for smooth and micro-structured surfaces (the proposed riblet shape, respectively and the presented new design of riblets with serration inside provides 7% drag reduction. The results do not show significant reduction in momentum transfer near the surface by riblets, in particular, around the outer region of the turbulent boundary layer. Conclusions with respect to the holistic investigation on the drag reduction with Serrate-Semi-Circular riblets have been drawn based on the research objectives as achieved. Recommendations for future work have been put forward particularly for further future research in the research area.Brunel University and KIMM (Korea Institute of Machinery and Materials

Design, Development and Thermal Analysis of Reusable Li-Ion Battery Module for Future Mobile and Stationary Applications

open access articleThe performance, energy storage capacity, safety, and lifetime of lithium-ion battery cells of different chemistries are very sensitive to operating and environmental temperatures. The cells generate heat by current passing through their internal resistances, and chemical reactions can generate additional, sometimes uncontrollable, heat if the temperature within the cells reaches the trigger temperature. Therefore, a high-performance battery cooling system that maintains cells as close to the ideal temperature as possible is needed to enable the highest possible discharge current rates while still providing a sufficient safety margin. This paper presents a novel design, preliminary development, and results for an inexpensive reusable, liquid-cooled, modular, hexagonal battery module that may be suitable for some mobile and stationary applications that have high charge and or discharge rate requirements. The battery temperature rise was measured experimentally for a six parallel 18650 cylindrical cell demonstrator module over complete discharge cycles at discharge rates of 1C, 2C and 3C. The measured temperature rises at the hottest point in the cells, at the anode terminal, were found to be 6, 17 and 22 °C, respectively. The thermal resistance of the system was estimated to be below 0.2 K/W at a coolant flow rate of 0.001 Kg/s. The proposed liquid cooled module appeared to be an effective solution for maintaining cylindrical Li-ion cells close to their optimum working temperature

Reconfigurable laser micro-processing systems: development of generic system-level tools for implementing modular laser micro-manufactoring platforms

Laser micro-machining (LMM) is an attractive manufacturing technology for the fabrication of a wide range of micro-components due to its intrinsic processing attributes. In addition, LMM can be integrated in hybrid manufacturing platforms and thus to combine LMM with other complementary processes for the cost effective fabrication of a broader range of miniaturised products. Nevertheless, the broader industrial uptake of LMM is still to come due to system-level issues in designing and implementing LMM systems. In this context, the research reported in this thesis is aimed at improving the system-level performance of reconfigurable LMM platforms and thus to create the necessary pre-requisites for achieving a much better machining accuracy, repeatability and reproducibility (ARR) in different processing configurations. First, a systematic approach for assessing and characterizing the manufacturing capabilities of LMM platforms in terms of ARR is proposed. Then, the development of generic integration tools for improving the system-level performance of reconfigurable LMM platforms in terms of manufacturing flexibility and reliability both as stand-alone machine tool configurations and also as component technologies in multi-process manufacturing solutions is presented. Next, generic software tools are proposed and validated for improving the manufacturing capabilities of LMM systems for realizing complex multi-axis laser processing strategies with a closed-loop manufacturing control. Finally, the integration of LMM in process chains is validated to extend the capabilities of well proven conventional manufacturing routes, i.e. micro milling, for the fabrication of miniaturised products, i.e. Terahertz technology devices, which have complex and challenging-to-fabricate functional features and overall designs

In-Situ Synthesis of Aluminum- Titanium Diboride Metal Matrix Hybrid Nanocomposite

Metal matrix nanocomposites (MMNC’s) are reported to have improved mechanical, thermal and electrical properties as compared to their respective base alloys. To date, these materials have been synthesized mainly by powder metallurgy or deformation processing. Solidification synthesis of MMNCs is a promising method, capable of economically producing large and complex shapes, however technical challenges including nanoparticle agglomeration, and poor interfacial strength have hindered the adoption of this technology. In-situ processing methods, in which the reinforcements are synthesized in liquid metals, typically via exothermic reactions offer the potential for improved dispersion and interfacial bonding between the reinforcement and the matrix, however this technique has been largely unexplored in the literature for metal matrix nanocomposites. The objectives of this research were to examine the feasibility of synthesizing nano or sub-micron size particulates in liquid aluminum using in-situ stir mixing and squeeze casting. An exothermic reaction was designed to synthesize Al2O3 and TiB2 from TiO2 particles and elemental boron in an aluminum melt. This dissertation investigates (i) the mechanism of aluminothermic and borothermic reduction of titanium oxide in the presence of molten aluminum and boron, (ii) in situ synthesis of micron and nano sized particles via solidification processing, and (iii) the effects of processing variables on the physical, microstructural, mechanical and tribological properties of in-situ MMNCs. Microstructural examination and theoretical analysis indicates that the reaction to form TiB2 and Al2O3 proceeds through several complex non-equilibrium reactions. A multi-stage reaction model is proposed to describe the process by which the TiO2 surface is reduced to form Al2O3 and TiB2. The effects of the powder particle size on the formation of reinforcing phases and microstructural evolution have been investigated and it was found that nanosized TiO2 powder promoted the formation of smaller size reinforcing phases. Furthermore, a solidification route has been designed to fabricate in-situ aluminum composites reinforced with submicron Al2O3 and TiB2 particulates. Experimental and theoretical analysis is presented that shows that the particle size and refining power of nanoparticles is controlled by the viscosity of the melt, rather than precipitation and growth. In addition, it was found that increasing the weight percentage of nanoparticles of TiO2 resulted in an increase in elastic modulus with good agreement to analytical models. Increasing the weight percentage of reinforcement up to 4 wt% resulted in an increase in the hardness greater than that predicted by the rule of mixtures or the Hall Petch relationship

Gas atomized precursor alloy powder for oxide dispersion strengthened ferritic stainless steel

Gas atomization reaction synthesis (GARS) was employed as a simplified method for producing precursor powders for oxide dispersion strengthened (ODS) ferritic stainless steels (e.g., Fe-Cr-Y-(Ti,Hf)-O), departing from the conventional mechanical alloying (MA) process. During GARS processing a reactive atomization gas (i.e., Ar-O2) was used to oxidize the powder surfaces during primary break-up and rapid solidification of the molten alloy. This resulted in envelopment of the powders by an ultra-thin (t \u3c 150 nm) metastable Cr-enriched oxide layer that was used as a vehicle for solid-state transport of O into the consolidated microstructure. In an attempt to better understand the kinetics of this GARS reaction, theoretical cooling curves for the atomized droplets were calculated and used to establish an oxidation model for this process. Subsequent elevated temperature heat treatments, which were derived from Rhines pack measurements using an internal oxidation model, were used to promote thermodynamically driven O exchange reactions between trapped films of the initial Cr-enriched surface oxide and internal Y-enriched intermetallic precipitates. This novel microstructural evolution process resulted in the successful formation of nano-metric Y-enriched dispersoids, as confirmed using high energy X-ray diffraction and transmission electron microscopy (TEM), equivalent to conventional ODS alloys from MA powders. The thermal stability of these Y-enriched dispersoids was evaluated using high temperature (1200yC) annealing treatments ranging from 2.5 to 1,000 hrs of exposure. In a further departure from current ODS practice, replacing Ti with additions of Hf appeared to improve the Y-enriched dispersoid thermal stability by means of crystal structure modification. Additionally, the spatial distribution of the dispersoids was found to depend strongly on the original rapidly solidified microstructure. To exploit this, ODS microstructures were engineered from different powder particle size ranges, illustrating microstructural control as a function of particle solidification rate. The consolidation of ultra-fine powders (dia. less than 5ym) resulted in a significant reduction in dispersoid size and spacing, consistent with initial scanning electron microscopy studies on as-atomized cross-sectioned particles that suggested that these powders solidified above the threshold velocity to effectively solute trap Y within the alpha-(Fe,Cr) matrix. Interestingly, when the solidification velocity as a function of particle size was extracted from the aforementioned theoretical particle cooling curves, it could be offered as supporting evidence for these microstructure observations. Thermal-mechanical treatments also were used to create and evaluate the stability of a dislocation substructure within these alloys, using microhardness and TEM analysis of the alloy sub-grain and grain structure. Moreover, elevated temperature tensile tests up to 800yC were used to assess the initial mechanical strength of the ODS microstructure

The Effect of Friction Stir Processing on The Microstructure and Tensile Behavior of Aluminum Alloys

Friction Stir Processing (FSP) is a promising thermomechanical technique that is used to modify the microstructure of metals locally, and thereby locally improve mechanical properties of the material. FSP uses a simple and inexpensive tool, and has been shown to eliminate pores and also reduce the sizes of intermetallics in aluminum alloys. This is of great interest for research on solidification, production and performance of aluminum alloy castings because FSP can enhance the structural quality of aluminum casting significantly by minimizing the effect of those structural defects. In the literature, there is evidence that the effectiveness of FSP can change with tool wear of the tool used. Therefore, a study was first conducted to determine the effect of FSP time on the tool life and wear in 6061-T6 extrusions. Results showed the presence of two distinct phases in the tool life and wear. Metallographic analyses confirmed that wear in Phase I was due to fracture of the threads of the tool and Phase II was due to regular wear, mostly without fracture. Moreover, built-up layers of aluminum were observed between threads. The microhardness profile was found to be different from those reported in the literature for 6061-T6, with Vickers hardness increasing continuously from the the stir zone to the base material. To investigate the degree of effectiveness of FSP in improving the structural quality of cast A356 alloys, ingots with different quality (high and low) were friction strir processed with single and multiple passes. Analysis of tensile test results and work hardening characteristics showed that for the high quality ingot, a single pass was sufficient to eliminate the structural defects. Subsequent FSP passes had no effect on the work hardening characteristics. In contrast, tensile results and work hardening characteristics improved with every pass for the low quality ingot, indicating that the effectiveness of FSP was dependent on the initial quality of the metal. The evolution of microstructure, specifically the size and spacing of Silicon (Si) eutectic particles, was investigated after friction stir processing of high quality A356 castings with single and multiple passes. Si particles were found to coarsen with each pass, which was in contrast with previous findings in the literature. The nearest neighbor distance of Si particles also increased with each FSP pass, indicating that microstructure became progressively more homogeneous after each pass. In the literature, the improvement observed after FSP of Al-Si cast alloys was attributed to the refinement of Si particles. Tensile data from high quality A356 ingot showed that there was no correlation between the size of Si particles and ductility. To the author’s knowledge, this is the first time that the absence of a correlation between Si particle size and ductility has been found

Understanding the Evolution of Surface Texture Under Boundary Lubrication

The objective of this research was to understand the evolution of surface texture under boundary/mixed lubrication (BL). Significant material/energy losses occur during BL because of direct contact between the two surfaces. Traditionally, tribofilms have been studied extensively for BL while textures have been used as a static engineering design parameter to enhance lubricant film properties. However, texture is dynamic at the tribological mating interface, where both physical and chemical interactions are continuously modulated. The evolution and the interplay between the tribofilm and texture is least studied in the literature, which is the focus of this research. MoS2-based lubricants, known for their excellent anti-friction and anti-wear performance [1]–[3], were used during the experiments. The experiments were divided into two parts; 1) polished steel discs were used to study directed organization/re-organization of surface asperities in correlation with tribofilm; 2) textured discs were used to study the effect of artificial texture on manipulation of tribofilm properties. Three stages of lubrication evolution, namely break-in, development, and steady-state, were discovered and studied experimentally. Surface texture was characterized using laser scanning microscope. Tribofilm morphology and chemistry was studied using scanning and transmission electron microscopy and Raman spectroscopy. The results showed that the surface roughness increases during break-in period and then stabilizes. Addition of directional texture results in early onset and stabilization of tribo-chemical reactions. Raman spectra confirmed presence of MoS2, FeS2, Fe2O3, and molybdate compounds, consistent with previous studies. [3] Cross-sectional TEM images revealed presence of stored lubricant in valleys while delivering lamellar tribo-layer on asperities. From the results, the following lubrication mechanism was discussed. Initially, during the break-in period, contact between mating surfaces results in re-organization/re-alignment surface asperities under the applied load and directional motion. Creation of fresh asperities in the presence of lubricant along with energy dissipation is responsible for the onset of tribo-chemical reactions. Subsequently, during the development stage, progressing reactions between surface asperities and lubricant lead to formation and stabilization of tribofilm. Eventually, in the steady-state, stabilized texture and tribofilm results in stable lubrication response. The findings of this research will benefit heavy-duty industrial applications involving low-speed, high-load conditions

Machinability studies of selective laser melted titanium alloy Ti-6Al-4V

This study focusses on exploring the mechanical properties and machinability characteristics of Selective Laser Melted titanium alloy Ti-6Al-4V. It provides insights on how machining and additive manufacturing can be used collaboratively to improve the productivity and product quality of end titanium components.<br /