We herein report an instability of a vortex ring, produced from the impact of a droplet of glycerol solution, penetrating in a water pool. The morphological and motional evolutions of the vortex ring have been captured using the high-speed shadowgraph technique. It is identified that the vortex ring undergoes a two-stage evolution with the disintegration as the turning point, namely, damping penetration and cyclic bifurcation, during which the viscous drag and gravity alternatingly dominate the penetrating behavior. We further propose two unified descriptions, respectively, for the penetration of the vortex ring before and after the disintegration and establish the instability criterion for both the disintegration and the bifurcation as well.

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Port fuel injection is an important technical route in methanol engines. To obtain a theoretical basis for injector arrangement and injection strategy development in methanol engines, an optimal experimental platform based on diffuse back-illumination and the refractive index matching method (RIM) was designed and built in this study. The experiments on the behavior of low-pressure methanol spray-wall impingement and wall film were carried out and the influence of the three boundary conditions of spray distance (Dimp), wall temperature (Twall), and injection pressure (Pinj) were analyzed comprehensively. Results showed that with the increase of Dimp, the overall shape of spray before impinging the wall changed from conical to cylindrical. The impinging spray height Hi and impinging spray width Wi increased with the decrease of Dimp and the increase of Pinj. Adhesive fuel film mass Mf increased with the increase of Dimp due to the decrease of kinetic energy during wall impact. In addition, the increase of the wall temperature Twall reduced Mf due to evaporation, but when Twall reached 423 K, Mf rebounded due to the Leidenfrost effect. The results of this study are helpful to improve the accuracy of the numerical methanol engine model.

For electric reliability and to save energy, the distributed power generation combining cooling and heating supply called a CCHP system for architectures has many potential advantages and is widely adopted to provide electric power and to satisfy local heating and cooling loads by waste heat recovery with low carbon intensity. However, the current CCHP system usually has a fixed ratio of the power and heat due to the features of its power unit, which leads to difficulties in the load management. In this paper, based on the operation of an internal combustion engine fueled with natural gas, a novel method is proposed and studied to achieve a controllable rate of heat/power to meet different load requirements of the electricity and heat (cooling or heating loads). By varying the ignition timing of the spark ignition engine, the combustion process within the cylinder can be adjusted to occur at different crank angles so that the engine crank shaft output power (related to the generated electricity) and the heat from the exhaust gas are changed accordingly. To study the effects of ignition timing on engine power and exhaust heat energy, a two-zone model was established with a predictive combustion model. The changes in the combustion process, output power, exhaust gas temperature, and heat energy were mostly our concern. The results show that the heat/electricity ratio can be adjusted from normally 1.0 to 1.6, and they can be controlled independently under partial load operating conditions. To solve the potential thermal failure of the turbine, the extraordinarily high exhaust temperature will be adjusted by compressed air.

Acoustic flame suppression is a potential technology which does away with the need to carry fire-extinguishing media and does not cause secondary pollution. We herein reported an experimental study on the displacement and extinction of jet diffusion flames exposed to speaker-generated traveling sound waves with a frequency of 110–150 Hz and local sound pressure of 2–16 Pa. The simultaneous movement of the flame and fuel was captured using a high-speed camera and schlieren techniques. Results showed that the flame oscillation was dominated by induced wind produced by membrane vibrations instead of sound pressure, and this induced wind’s frequency was the same as that of sound waves. Moreover, the movement of unburned fuel and flame was not synchronous, which resulted in an interrupted fuel–flame cycle. Consequently, the flame was gradually suppressed and completely extinguished after several oscillation cycles. Finally, we determined the extinction criterion that when the dimensionless gap between the flame and the unburned fuel was greater than or equal to 7, the flame would be extinguished. Results clearly revealed the mechanism of acoustic fire extinguishing, which provided reference for the feasibility of acoustic fire-extinguishing applications.