Proton exchange membrane fuel cells (PEMFCs) using porous metallic foam flow-field plates have been demonstrated as an alternative to conventional rib and channel designs, showing high performance at high currents. However, the transport of liquid product water through metal foam flow-field plates in PEMFC conditions is not well understood, especially at the individual pore level. In this work, ex-situ experiments are conducted to visualise liquid water movement within a metal foam flow-field plate, considering hydrophobicity, foam pore size and air flow rate. A two-phase numerical model is then developed to further investigate the fundamental water transport behaviour in porous metal foam flow-field plates. Both the experimental and numerical work demonstrate that unlike conventional PEMFC channels, air flow rate does not have a strong influence on water removal due to the high surface tensions between the water and foam pore ligaments. A hydrophobic foam was seen to transport liquid water away from the initial injection point faster than a hydrophilic foam. In ex-situ tests, liquid water forms and maintains a random preferential pathway until the flow-field edge is reached. These results suggest that controlled foam hydrophobicity and pore size is the best way of managing water distribution in PEMFCs with porous flow-field plates.

This article describes a proper-orthogonal-decomposition (POD) based methodology proposed for the identification and separation of coherent and turbulent velocity fluctuations. Typically, POD filtering requires assumptions to be made on the cumulative energy content of coherent modes and can therefore exclude smaller, but important contributions from lower energy modes. This work introduces a suggested new metric to consider in the selection of POD modes to be included in a reconstruction of coherent and turbulent features. Cross-correlation of POD spatial modes derived from independent samples is used to identify modes descriptive of either coherent (high-correlation) or incoherent (low-correlation) features. The technique is demonstrated through application to a cylinder in cross-flow allowing appropriate analysis to be carried out on the coherent and turbulent velocity fields separately. This approach allows identification of coherent motions associated with cross-flow transport and vortex shedding, such as integral length scales. Turbulent flow characteristics may be analysed independently from the coherent motions, allowing for the extraction of properties such as turbulent length scale.

Cylinder deactivation, sometimes referred to as variable displacement engine technology, is a method being employed in state-of-the-art reciprocating engines to improve fuel economy. The approach involves disabling the valve actuation of one or more cylinders to deactivate them, thus forcing the engine to operate at a higher specific load across the remaining cylinders to produce the torque demanded. Operating at such a point with an increased throttle opening reduces the engine’s pumping losses and hence reduces fuel consumption. In this work, the spray morphology, combustion and emissions of a three-cylinder downsized gasoline turbocharged direct injection engine with variable displacement engine capability on one cylinder were studied. This investigation allowed the interaction between the fuel spray, engine performance and emissions immediately following the reactivation of the deactivated cylinder to be better understood. Three operation modes were examined which included running the engine at full displacement, at the reduced displacement and at full displacement with increased indicated mean effective pressure, matching that of the reduced displacement mode. The study showed that cylinder deactivation significantly reduced specific fuel consumption at the conditions tested in comparison to full displacement operation. It was also found that when running the engine at full displacement but with the reduced displacement–level indicated mean effective pressure, the specific fuel consumption was greater than for reduced displacement operation. In addition, it was observed that particulate number emissions increase transiently during the deactivation period due to the disturbances to the fuelling control caused by displacement transitions. Improved fuelling control, refinement of the engine calibration during reduced displacement operation or a gasoline particulate filter could be used to manage this particulate number level.

Phase-locked particle imaging velocimetry measurements are carried out in a direct-injected spark-ignition single-cylinder optical research engine equipped with fully variable valve timing to assess the impact of asymmetric intake valve lift strategies on the in-cylinder flow. The engine was operated under a range of asymmetric strategies, with one valve following a full lift profile, while the second intake valve is scaled as a factor of the first, expressed as % maximum valve lift. Proper orthogonal decomposition combined with a proposed methodology allows instantaneous velocity fields to be decomposed into what are nominally demonstrated as coherent and turbulent constituent velocity fields. Analysis of the coherent fields reveals the behaviour of large-scale structures within the flow, subject to cyclic variation. In the case of 40% maximum valve lift, an increase in the flow cyclic variability is observed. This is found to be as a result of a switch between a flow dominated by a counter-rotating vortex pair and a single vortex. The impact of maximum valve lift on the bulk motion is further evident by an increase in the magnitude of swirl ratio from 0.5 to −6.0 (at 75°CA). Analysis of the turbulent constituent shows how the increased valve life asymmetry leads to increased turbulence during the intake stroke by over 250%. Finally, it is shown how the ensemble turbulence statistics may be misleading as stochastic fluctuations were found to be typically 66% of the total turbulent kinetic energy calculated from the ensemble statistic in the tested conditions.