New high efficiency engine combustion modes hold the promise to significantly reduce the contribution of transport vehicles to climate change. All of these modes rely upon direct injection of fuel into the combustion chamber, and so fuel/air mixture preparation is a controlling process in terms of engine efficiency (i.e. reduced CO2 production) and pollutant emissions (including soot, another contributor to climate change). As these new combustion modes push to higher pressure and temperature, it would appear that the fuel jets probably undergo a thermodynamic change, becoming supercritical at the edges of the jet. If that were true, it would completely change our current understanding of fuel/air mixture preparation, and that would have a significant effect on engine performance and design. At this time several theory groups are in disagreement on whether or not this change happens, and if it does how best to understand it. This project will resolve those disagreements, and it will lead to the understanding required to adapt both fuel injectors and engines to this potential new reality. Aside from the motor industry, supercritical mixing is important to the pharmaceutical, food processing, catalyst production, and other nanomaterials industries, and our goal is to team with researchers in these areas as well. This project has four main parts. A specialized, optically-accessible cell will be designed and built based on a successful design under operation at the Technical University of Darmstadt. A laminar liquid jet (with clear access to the fluid/gas interface) will flow down through this chamber, which can be set to various pressures and temperatures below and above the liquid critical point. A line-Raman scattering instrument will be developed in order to characterize the chemical composition of the flowfield as a function of time and position. Next, laser induced thermal acoustics (LITA) will be developed. LITA will be used to measure the sound speed as a function of position and time as conditions are varied. The sound speed reaches a minimum at the critical point, and increases very steeply as pressure and temperature go above the critical point, so it can be a significant marker for thermodynamic states. Finally, Förster resonance energy transfer (FRET) will be evaluated as a way to observe changes in the density (mean free path) as the jet approaches a supercritical state. Such a change is considered to be a distinctive marker for this state as well. This program has been designed specifically for our theory partners (City University London, Sandia National Labs, Stanford University, and University of Wisconsin), who have taken part in planning discussions for this proposal. We will thus use the experiments to provide quantitative information never before available to academia or to industry. The information will provide unambiguous, quantitative results with two aspects: 1) Industry can use them to re-think their mixture preparation strategies, while 2) theoreticians can use the results to inform and validate models. Ultimately those models will be delivered to industry. As mentioned, there are many other subject areas interested in similar problems. Once this system is operating well we will approach UK researchers working in related areas and offer this facility for collaborative research. The US Air Force Office of Scientific Research has committed to support partially this effort, with $360,000.

Almost all engineering systems and many biological ones contain components that are loaded and rub against one another, such as gears and bearings in machines and hip and knee joints in humans. This rubbing results both in friction, that wastes energy, and in wear and other forms of surface damage that lead to machine (and human) downtime, and the need for expensive repair and replacement. This whole field of research is called Tribology and is pivotal both in the quest for sustainability, including reducing CO2 emissions, and in improving the quality of our lives. In Tribology the effects of rubbing, such as frictional dissipation and wear, are perceived as macroscale phenomena and are traditionally studied by macroscale experiments and analysis. However they actually originate at the atomic and molecular scale, where the severe local stresses produced by rubbing cause restructuring of surface layers, while the molecules of lubricant in rubbing contacts interact with and protect surfaces. Thus to understand and so improve tribological systems we need an approach that spans the molecular, meso- and macro-scales. This will yield both information as to the origins of friction and surface damage - and unwanted phenomena are best tackled at their roots - as well as the ability to design macro-scale components such as lubricants, bearings, gears, engines and replacement joints that operate reliably and efficiently for as long as required. To meet this need, the proposed research will develop and apply advanced techniques to model rubbing contacts at all the necessary scales - atomic/molecular simulations of surfaces and lubricants, meso-scale modelling looking at structural evolution of surfaces due to rubbing, and macro-scale simulations of actual rubbing components such as bearings and engines. These simulations will be validated by experiments that also span the same range of scales, including direct observation of molecules in rubbing contacts. The most critical and innovative stage of this project, however, will be to link all these models together in to a single computer-based package. The result will be a set of modelling programs that can be used in many different ways; for example to explore the origins of tribological phenomena; to optimise lubricant surface and materials design; to predict performance of machines based on a combination of design and underlying atomic/molecular processes. Such an approach will give us tools both to understand in full tribological phenomena such as friction and wear and to enable effective "virtual testing", where new and novel designs, lubricants and surfaces can be combined and their effectiveness tested prior to recourse to time-consuming and expensive experimental development.

Friction plays a central role in life; in transport, in manufacturing, in process engineering, in medical devices and in everyday human activities. Friction has commanded the attention of Amontons, Coulomb and Da Vinci and their simplistic, empirical laws have been the cornerstone of friction theory. At the conceptual and theoretical levels the vast modern day friction literature has revealed the enormous complexity of even the simplest processes and the limitations of the early friction laws. Friction is intimately linked to both adhesion, contact geometry and wear and all require an appreciation of the highly non-equilibrium and non-linear processes occurring over multiple length scales. The challenge presented is that friction in realistic engineering contacts cannot be predicted. Understanding the physical and chemical processes at contacting interfaces is the only route to cracking the tribological enigma. The research gap addressed in this Programme Grant is linked to the development of accurate experimental and numerical simulations of friction. We appreciate that the search for a unified model for friction prediction is futile because friction is system dependent. However, the goal to predict friction is achievable. We have identified 4 key areas where there are current challenges in understanding the origins of friction because of different complexities as outlined below: - Reactive surfaces; in many systems the frictional contact brings about chemical reactions that can only be described by non-equilibrium thermodynamics. We need accurate kinetic rate data for reactions which can only be provided by advanced in-situ chemical analysis - Extreme interfaces; these can be described as any interfaces that are inducing high strain rate material deformation and combined with electrochemical or chemical reactions. Simulation and sensing are key to improving the understanding. - Non-linear materials; in engineering and in biological systems we see the evolution of "soft" materials for tribological applications. Predicting friction in these systems relies on understanding the rheology/tribology interactions. - Particles and 2nd phase materials; for materials processing or for understanding the transport of wear particles in a contact we need to understand particle-particle friction in complex contact conditions where fracture/deformation are occurring.

The machines, products and devices all around us are full of moving parts; from the tiny read/write head in a hard drive, the prosthetic hip joint, the high speed train rail/wheel interface, the most powerful jet engine, to the giant gearboxes in wind turbines. It is the interacting surfaces in these moving parts where friction occurs and energy is lost. Lubrication is required to control friction and minimise the wear that causes premature failure. Selection of suitable rubbing materials and surface treatments helps to make parts last longer. Tribology is the science that encompasses the study of friction, wear, lubrication and surface engineering. It is a true underpinning technology behind developments in all industry sectors. This proposal is for a Centre for Doctoral Training in Integrated Tribology (iT-CDT) to act as a training school and centre for research excellence in tribology. We have established a number of industrial partners who are prepared to make significant cash commitment to the Centre. They will benefit from a supply of highly trained PhD graduates, research focussed on their industry needs, as well as access to a pool of research on generic pre-competitive themes. The two universities are fully supportive of the bid and are providing studentships, staff time, and facilities. The total gearing proposed is £3.75M (45%) from EPSRC, £2.2M from industry (26%), and £2.4M (29%) from the universities. Integrated Tribology Integrated across disciplines - the nature of tribology is such that a multi-disciplinary approach is essential: physics of surfaces, chemistry of lubricants, material and surface treatment technologies, and engineering design. The iT-CDT plans to recruit PhD students and undertake PhD projects that span the disciplines of physics, chemistry, materials science and mechanical engineering. Integrated across industrial sectors - tribology is an underpinning technology in all industry sectors. Many industries face the same generic problems (e.g. operating with thinning films, minimising and/or control of friction, fuel efficiency, reducing maintenance, extreme environments). The iT-CDT plans to integrate across sectors, sharing research expertise and common themes. Integrated over the product life cycle - tribology is involved at all stages of a product lifecycle - from design, manufacture, maintenance, repair, through to disposal. The iT-CDT plans to have projects that span these stages of the lifecycle and to train students in the appreciation of the lifecycle and its sustainability. Integrated across length scales - when surfaces rub together, atomic forces at the interface are responsible for friction and adhesion. The molecular structure of the lubricant and its chemical formulation provide protection. Interaction at this nano-scale governs performance at the macro-scale. The iT-CDT plans to integrate across length scales, combining analysis and methods from nano- to macro- in each project. Integrated across technology readiness level - The iT-CDT plans to give students experience of the different types of research. The Centre's structure of mini-projects, research, and a final impact project will give scope for fundamental pre-competitive research, consultancy type problem solving, and application of research in an industrial environment, respectively.