No abstract

Summary 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.

Summary A travelling‐wave thermoacoustic refrigerator driven by a cascade thermoacoustic engine is evaluated experimentally in this paper. A prototype is developed under the constraint of a low‐cost and less complicated device. In order to reduce the total budget, commercial materials and standard parts are selected, and air at atmospheric pressure is used as working fluid in the system. The thermoacoustic coupled engine‐refrigerator system consists of 1 standing‐wave unit, 1 travelling‐wave unit, and 1 travelling‐wave refrigerator arranged in a linear configuration. A resonator‐tube is connected at each end of the thermoacoustic core. The effects of the length and hydraulic radius of the regenerator in the refrigerator on the cooling performance are investigated at different levels of input power. In the experimental results, the maximum temperature difference of 17.6°C was realised at the no‐load condition. The maximum coefficient of performance relative to Carnot (COPR) of 2.4% was accomplished at the cooling load of 13 W.

No abstract

No abstract

No abstract

No abstract

a b s t r a c tThis work presents the development and implementation of auto-ignition modelling for DI diesel engines by using the PDF-Eddy Break-Up (PDF-EBU) model. The key concept of this approach is to combine the chemical reaction rate dealing with low-temperature mode, and the turbulence reaction rate governing the high-temperature part by a reaction progress variable coupling function which represents the level of reaction. The average reaction rate here is evaluated by a probability density function (PDF) averaging approach. In order to assess the potential of this developed model, the well-known Shell ignition model is chosen to compare in auto-ignition analysis. In comparison, the PDF-EBU ignition model yields the ignition delay time in good agreement with the Shell ignition model prediction. However, the ignition kernel location predicted by the Shell model is slightly nearer injector than that by the PDF-EBU model leading to shorter lift-off length. As a result, the PDF-EBU ignition model developed here are fairly satisfactory in predicting the auto-ignition of diesel engines with the Shell ignition model.