The problem of fouling in the heat exchangers of exhaust systems has yet to be resolved. This results in enormous costs for engine manufacturers due to the required over-sizing during design and due to unscheduled maintenance needs.This article presents an experimental layout developed for measuring fouling in diesel engine exhaust gas systems. This facility was based on a circular cylindrical cross-flow device, with one straight and smooth stainless steel probe positioned transverse to the flow of exhaust gases. The probe can be cooled from the inside with water and fouled on the outside as a result of particle deposition from exhaust gases.The tests were conducted under constant engine operating conditions. Therefore, the asymptotic depth of the fouling layer could be measured at different angular positions at the end of each test.The critical wall shear stress rate is proposed as the controlling mechanism of the local removal process that leads to different fouling depths around each probe. This is in contrast to the critical velocity concept, which cannot be applied at a local scale due to its formulation. The experimental results, although subject to the usual uncertainties of fouling processes, seem to support this idea.

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A highly accurate SPH method with a new stabilization paradigm has been introduced by the authors in a recent paper aimed to solve Euler equations for ideal gases. We present here the extension of the method to viscous incompressible flow. Incompressibility is tackled assuming a weakly compressible approach. The method adopts the SPH-ALE framework and improves accuracy by taking high-order variable reconstruction of the Riemann states at the midpoints between interacting particles. The moving least squares technique is used to estimate the derivatives required for the Taylor approximations for convective fluxes, and also provides the derivatives needed to discretize the viscous flux terms. Stability is preserved by implementing the a posteriori Multi-dimensional Optimal Order Detection (MOOD) method procedure thus avoiding the utilization of any slope/flux limiter or artificial viscosity. The capabilities of the method are illustrated by solving one- and two-dimensional Riemann problems and benchmark cases. The proposed methodology shows improvements in accuracy in the Riemann problems and does not require any parameter calibration. In addition, the method is extended to the solution of viscous flow and results are validated with the analytical Taylor–Green, Couette and Poiseuille flows, and lid-driven cavity test cases.

The enormous amount of waste heat that is rejected through the exhaust system in a modern engine is possibly the main source of energy yet to be converted into power on a conventional internal combustion engine. The groups of technologies exploiting this source of energy are normally called Waste Heat Recovery (WHR) systems. The most promising WHR technology under development is probably the low pressure Rankine cycle employing an organic working fluid. The strong interaction between the WHR system with the exhaust and cooling systems of the engine, combined with the inherent transient nature of the engines employed in transportation, makes the correct design, sizing and construction of its main components especially challenging. In this work, commercial 1-D software is employed to model the recovery system. The system consists of two boilers, one in the main exhaust line and another in the exhaust gas recirculation circuit. These boilers generate high pressure vapour that is expanded to obtain power. The low pressure vapour leaving the expander is used to preheat the high pressure liquid at the exit of the pump, while the cooling system of the engine is used to convert the low pressure, low temperature vapour into liquid in the condenser. Finally, a positive displacement pump is employed to heighten the pressure of the liquid. For this, R245-fa will be used as operating fluid. To build the model of the whole system, specific geometrical and material aspects of each main component are required. This information is based on state-of-the-art equipment and on experimental information available for the calibration of each subsystem. A parametric optimization of the main operational parameters of the WHR, is done to optimize the performance of the different systems and integration with the engine. Finally, the whole system is simulated under different load conditions of the engine to obtain its overall performance.

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