Development and application of the drop number size moment modelling to spray combustion simulations

This work presents the development and implementation of spray combustion modelling based on the spray size distribution moments. In this spray model, the droplet size distribution of spray is characterised by the first four moments related to number, radius, surface-area and volume of droplets, respectively. The governing equations for gas phase and liquid phase employed are solved by the finite volume method based on an Eulerian framework. These constructed equations and source terms are derived based on the moment-average quantities which are the key concept for this work. The sub-model employed for ignition and combustion is the coupling reaction rate between Arrhenius model and Eddy Break-Up model (EBU) via a reaction progress variable. The results obtained from simulation are compared with the experimental and simulation data in the literature in order to assess the accuracy of present model. Comparing with the experimental results, present approach is capable to provide a qualitatively reasonable prediction for auto-ignition. In addition, the flame area developed during the combustion progress corresponds with the experimental data.     

Application of spray combustion simulation in DI diesel engine

This work presents the development and implementation of combustion model for DI diesel engines by using the PDF-Chemical Equilibrium combustion model. The key concept of this approach is to predict the thermochemical variables (e.g., temperature, species mass fractions) and then the average scalars of these variables are evaluated by a probability density function (PDF) averaging approach. To realize flame propagation, the reaction time scale is employed to relax the infinitely fast chemistry of chemical equilibrium. The PDF-Eddy Break Up ignition model is adopted in the auto-ignition calculation. With regard to the comparison results, the simulation results are in good agreement with the experimental results in both ignition and combustion modes. In addition, the predicted lift-off length also corresponds to a power-law scaling of Siebers et al.     

The performance improvement of a cascade thermoacoustic engine by adjusting the acoustic impedance in the regenerator

A novel cascade configuration consisting of one standing wave unit and one travelling wave unit arranged in series is studied in this paper. Theoretically, a straight‐line cascade engine provides an efficient energy conversion, reduces the difficulties of fabrication and allows no Gedeon streaming. In order to achieve such a powerful cascade thermoacoustic engine, the regenerator of the travelling wave unit must be operated in high impedance and travelling wave phasing region. Various techniques of phase adjustment by modifying the configurations and geometrical dimensions of the system are investigated both numerically and experimentally in order to adjust the position of the sweet spot as well as to promote the acoustic impedance in the regenerator. It is found that the effective tuning methods with less modification here are accomplished by changing the volume of down‐cavity and reducing the flow area of down‐resonator by inserting the pencil. The exploration also shows that the acoustic field in the system is quite sensitive to the effect of down‐resonator length. The performance of the proposed system is clearly improved after the phase‐adjustment schemes are completely implemented, in which the regenerator works within the sweep spot zone with high acoustic impedance. Copyright © 2016 John Wiley & Sons, Ltd.