Wärtsilä (Finland)

Model-based calibration of high-efficient reactivity controlled compression ignition (RCCI) engines popularly rely on chemical-kinetics based multizone models (MZM) for predictive, performance-oriented simulations. These models however, employ heuristic approaches to capture the critical phenomena of direct-injected fuel stratification and interzonal mixing, which limit their utility. These issues are presently addressed by (i) developing a semi-predictive fuel stratification sub-model; and (ii) implementing in-cylinder mixing based on the turbulence energy cascade mechanism. The simulations are parameterized to the latest line-up of Wärtsilä’s 20DF marine engines, with model calibration additionally supported by CFD results on this target cylinder geometry. Operating on natural gas and diesel fuelled RCCI, validation against the engine measurements reveals correct sensitivities to all combustion control parameters including injection timing and duration, and boost pressure. The MZM’s prediction accuracy is within 1.5°CA for combustion phasing, and all synthetic performance indicators, derived from pressure trace, are within 5% error. Additionally, the model reproduces the traces of mass averaged turbulent kinetic energy and turbulent viscosity within a relative root mean square error of 10% with respect to detailed CFD results. The realistic fuel distribution and improved interzonal mixing allows for accurate predictions of nitrogen oxides and hydrocarbon emissions in-line with state-of-the-art MZMs. With an average simulation time below 4 min per cycle, makes the improved MZM viable for rapid prototyping next-generation RCCI engines.

A crack propagation finite-element model of interior defect-initiated short cracks under near-threshold loading conditions is used to investigate the effect of plasticity-induced crack closure in the presence of a single overload and underload. The effect of an overload predicted by the present model is qualitatively very similar to what is commonly reported, but in this case an underload produces a differing result to the literature consensus, yielding a similar but weaker effect as the overload. Extended acceleration of crack propagation due to a single underload might not be attributable to plasticity-induced crack closure under plane strain conditions. A distinct crack profile shape consequent of crack tip blunting is present with both loading irregularities. A new method for examining crack closure for the entire crack surface is presented.

The effect of a rough, textured surface and contact orientations on the fretting behavior of self-mated martensitic 34CrNiMo6 +QT steel was examined via a large annular flat-on-flat contact. A friction study accompanied by microscopy analyses was performed to provide a clear insight into fretting characteristics. In gross sliding, the rough surface revealed a lower delayed friction peak and the same steady-state friction as the fine-ground smooth one. In partial slip, the stable friction threshold was around 0.5 for both surfaces. The oxidation-abrasion and its combination with adhesion were observed as wear mechanisms in partial slip and gross sliding, respectively.

Commercial shipping alone is responsible for transporting 90% of world trade. That’s a merchant fleet of more than 50,000 ships, worth around US$1.8 trillion, transporting an estimated 11 billion tons of goods each year.1 Typically, transporting that Amazon parcel from A to B involves multiple companies which must all be aligned if the efficiency, safety, and resilience of maritime operations are to be optimized.

<div class="section abstract"><div class="htmlview paragraph">The paper presents novel studies on the impact of different ignition control parameters on combustion stability and spark plug wear. First, experimental results from a 32.4-liter biogas fueled large bore single cylinder spark ignition engine are discussed. Two different ignition systems were considered in the experiment: a DC inductive and an AC capacitive. The spark plugs used in the experiment were of dual-iridium standard J-gap design of different electrode gaps. Test results show the importance of different degrees of freedom to control a spark. A robust ignition is found to be achieved by using a very short spark duration, which in turn reduces total energy discharge at the gap. Further observations reveal that once a stable and self-propagating flame kernel is developed, it becomes independent of the spark energy further added to the gap. Finally, results from the spark plug wear tests using a pressurized rig chamber are discussed. It is found that an excessive spark energy discharge at the gap contributes to high erosion of spark plug electrodes, which is not desirable. However, spark energy is not the only factor affecting spark plug erosion. It is also the type of spark discharge (DC/AC) that governs the electrode wear over time. Therefore, the advantage of an AC spark discharge over a DC spark has been well established through the experimental results. The inherent property of an AC spark is found to be significantly slowing down electrode wear over time, hence increasing the service life of a spark plug.</div></div>