Jingyu Zhu

An investigation of the effects of fuel injection pressure, ambient gas density and nozzle hole diameter on surrounding gas flow of a single diesel spray by the laser-induced fluorescence–particle image velocimetry technique:

The characteristics of ambient gas motion induced by a single diesel spray were measured quantitatively by using a laser-induced fluorescence–particle image velocimetry technique under non-evaporating quiescent conditions. The effects of fuel injection pressure, ambient gas density and nozzle hole diameter on the ambient gas mass flow rate into the spray through the whole spray periphery (spray side periphery and tip periphery) were investigated quantitatively according to the gas flow velocity measurements. The results show that the captured gas mass flow rate through the spray tip periphery is prominent in the whole periphery and the proportion of the gas entrainment through the spray side periphery increases with spray development. The higher injection pressure significantly enhances the total gas mass flow rate through the whole periphery; however, the increase in the ratio of ambient gas and fuel mass flow rate becomes moderate gradually with the increase in the injection pressure. The higher ambient gas density results in a slight increase in ambient gas flow velocity along the spray side periphery and the tip periphery and a reduction of the spray volume; however, the ambient gas mass flow rate was apparently enhanced. The smaller nozzle hole diameter results in a significant decrease in the ambient gas mass flow rate and an increase in the ratio of the gas and fuel mass flow rate. Numerical simulation results provide more understanding of the spray-induced gas flow field and validate the measurement accuracy of the laser-induced fluorescence–particle image velocimetry results.

Effects of micro-hole nozzle and ultra-high injection pressure on air entrainment, liquid penetration, flame lift-off and soot formation of diesel spray flame:

Increasing the injection pressure and downsizing the nozzle orifice diameter have been major measures for diesel engines to facilitate fuel–ambient gas mixture formation and combustion processes. The objective of this investigation is to carry out a quantitative analysis on the effects of micro-hole nozzle and ultra-high injection pressure on the mixing and combustion characteristics of diesel spray flame. Hence, laser-induced fluorescence and particle image velocimetry technique was employed to quantitatively access the gas entrainment of diesel spray emerging from nozzle with orifice diameter down to 80 µm under injection pressure up to 300 MPa, together with OH* chemiluminescence imaging and two-color pyrometry techniques to resolve the combustion and soot formation processes. Additionally, numerical simulation on the multi-phase flow inside injector nozzle was conducted to obtain information on internal flow dynamics. Experimental results show that over 80% of the ambient gas entrained into a spray plume is through the capturing effect at its tip, followed by the entraining effects at its peripheral boundary. Moreover, both a decrease in orifice diameter and an increase in injection pressure result in enhancement of the instantaneous gas to fuel mass flow rate ratio, shortening of liquid length of spray under evaporating conditions. The lift-off length of a diesel spray flame is substantially extended by the increase in injection pressure, and slightly shortened by the decrease in nozzle orifice diameter. Additionally, the numerically acquired velocity and turbulence data at the nozzle exit plane provide interpretation on the variations of liquid length and lift-off length under different injection conditions. Finally, the combination use of micro-holes and ultra-high injection pressure greatly accelerate the mixing of fuel and ambient gas, avoiding the interference of liquid length and lift-off length, and drastically decreasing the soot formation.

Fuel Spray Combustion of Waste Cooking Oil and Palm Oil Biodiesel: Direct Photography and Detailed Chemical Kinetics

Ignition processes in engines is characterized by physical processes i.e. atomization and vaporization and chemical processes i.e. influence of cetane, oxygen content, and fuel molecular structure. Due to its future prospects in reducing emissions, it is crucial to investigate the physical and chemical ignition processes of biodiesel fuel whose physical and chemical properties are different from the conventional diesel fuel.