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First-order elliptic Conditional Moment Closure (CMC), coupled with a computational fluid dynamics (CFD) solver, has been employed to simulate combustion in a direct-injection heavy-duty diesel engine. The three-dimensional structured finite difference CMC grid has been interfaced to an unstructured finite volume CFD mesh typical of engine modelling. The implementation of a moving CMC grid to reflect the changes in the domain due to the compression and expansion phases has been achieved using an algorithm for the cell addition/removal and modelling the additional convection term due to the CMC cell movement. Special care has been taken for the boundary conditions and the wall heat transfer. An operator splitting formulation has been used to integrate the CMC equations efficiently. A CMC domain reduction of the three-dimensional problem to two- and zero-dimensions through appropriate volume integration of the CMC equation has been explored in terms of accuracy and computational time. Additional considerati...

The autoignition of a gaseous n-heptane plume in heated turbulent air has been investigated experimentally and numerically with the conditional moment closure and a CFD code. It has been demonstrated that, consistent with previous experimental results for hydrogen and acetylene, the increased scalar dissipation rate created by faster co-flowing air delays autoignition, as revealed by a disproportionate increase of ignition length with air velocity. The predicted mean and variance of the mixture fraction, the mixture fraction PDF and the conditional scalar dissipation rate are in good agreement with experimental results obtained with acetone-tracer PLIF. The first-order, spatially averaged CMC model reproduces the experimental trends quite well, despite the neglect of conditional fluctuations and spatial dependence of the conditional averages. This is attributed to the fact that for a significant period of time before autoignition the conditional scalar dissipation rate at the most reactive mixture fraction is much smaller than the critical value above which autoignition is precluded.

The unsteady two-dimensional conditional moment closure (CMC) model with first-order closure of the chemistry and supplied with standard models for the conditional convection and turbulent diffusion terms has been interfaced with a commercial engine CFD code and analyzed with two numerical methods, an “exact” calculation with the method of lines and a faster fractional-step method. The aim was to examine the sensitivity of the predictions to the operator splitting errors and to identify the extent to which spatial transport terms are important for spray autoignition problems. Despite the underlying simplifications, solution of the full CMC equations allows a single model to be used for the autoignition, flame propagation (“premixed mode”), and diffusion flame mode of diesel combustion, which makes CMC a good candidate model for practical engine calculations. It was found that (i) the conditional averages have significant spatial gradients before ignition and during the premixed mode and (ii) that the inclusion of physical-space transport affects the calculation of the autoignition delay time, both of which suggest that volume-averaged CMC approaches may be inappropriate for diesel-like problems. A balance of terms in the CMC equation before and after autoignition shows the relative magnitude of spatial transport and allows conjectures on the structure of the premixed phase of diesel combustion. Very good agreement with available experimental data is found concerning ignition delays and the effect of background air turbulence on them.

Atypical femoral fractures can be subsequent to a long-term biphosphonates treatment; they have a high frequency of delayed healing. The authors describe a femoral pseudoarthrosis of an atypical fracture treated with intramedullary nailing in a female after prolonged alendronate therapy. Atypical femoral fractures can be subsequent to a long-term biphosphonates treatment even if, in the literature, there is no clarity on the exact pathogenetic mechanism. The Task Force of the American Society for Bone and Mineral Research described the major and minor features to define atypical fractures and recommends that all the five major features must be present while minor features are not necessary. Another controversial aspect regarding the atypical femoral fractures is the higher frequency of the delayed healing that can be probably related to a suppressed bone turnover caused by a prolonged period of bisphosphonates treatment. This concept could be corroborated by the Spet Tc exam. In the case of a pseudoarthrosis, there is not a standardization of the treatment. In this report, the authors describe a femoral pseudoarthrosis of an atypical fracture treated with intramedullary nailing in a female after prolonged alendronate therapy; the patient was studied with clinical, bioumoral end SPECT-Tc exam of both femurs. Many studies show the relationship between bisphosphonates and the presence of atypical fractures. These fractures should be monitored more closely due to the risk of nonunion and they require considering an initial treatment with pharmacological augmentation to reduce the complications for the patient and the health care costs.