Hongzhi Sheng

The droplet group microexplosions in water-in-oil emulsion sprays and their effects on diesel engine combustion

To clarify the combustion mechanism of water-in-diesel fuel emulsion sprays and to evaluate the possible benefit of emulsions in practical usage, combustion bomb experiments, dynamic engine tests, and computer simulation were carried out, and some useful conclusions have been reached. The droplet group (lump-fashioned) microexplosions in water-in-diesel fuel emulsion sprays on an eddysizescale during the atomization, evaporation, and combustion processes in a high-pressure, high-temperature bomb were observed with a multipulsed, off-axis, image-plane, ruby laser holocamera and a highspeed camera. The explosions eject droplet fragments from the spray region to several millimeters away, improving the fuel-air mixing process and speeding up the flame propagation. A no-water layer formed by a Hill vortex was also observed in emulsion droplets. The ambient temperature has the most important influence on the occurrence and violence of the microexplosion. Road-load-simulation engine tests were carried out on a dynamic engine test bed. The experimentalresults show that emulsion fuels have no significant influence on fuel consumption and reduce engine torque if no adjustment is made for the injection system, but that smoke emission is much improved when emulsion fuel is used. The combustion characteristics and the rate of heat release are also analyzed to reveal the difference between emulsion and diesel fuel. The relationships between the optimum water percentages and fuel consumption under various operating conditions were analyzed by numerical combustion modeling.

Heat-Transfer Study of External Superheater of CFB Incinerator

The heat transfer coefficients for horizontally immersed tubes have been studied in model internally circulating fluidized bed (ICFB) and pilot ICFB incinerators. The characteristics in the ICFB were found to be significantly different from those in a bubbling bed. In ICFB, there is a flowing zone with high velocity, a heat exchange zone, and a moving zone with low velocity. The controllable heat transfer coefficients in ICFB strongly depend on the fluidized velocity in the flowing zone, and also the flow condition in the moving zone. The heat exchange process and suitable bed temperature can be well controlled according to this feature. Based on the results of experiments, a formulation for heat transfer coefficient has been developed. These results were applied to an external superheater of a CFB incinerator with a 450 °C steam outlet in a waste-to-energy pilot cogeneration plant of 12 MW in Jiaxing City, China.