The Effect of Fuel Injection Equipment of Water-In-Diesel Emulsions on Micro-Explosion Behaviour

Abstract

The number and size distributions of the water dispersed phase have a significant effect on both the long-term stability of an emulsion, and the probability of micro-explosions inside an engine. The emulsions are subjected to intense pressure and shear flow in the fuel injection equipment resulting in changes in the number and size distributions of the dispersed phase. These changes, in turn, have significant effects on the micro-explosion behavior of the droplets. To our knowledge, these effects are not known and have not been reported previously. To uncover some of these effects we carried out a comprehensive experimental investigation on an emulsion spray of 10% water (by volume) in diesel at different injection pressures of 500, 1000 and 1500 bar. A measurement system consisting of a high-speed camera was used to visualize the droplets' micro-explosions and a thermocouple measured the temperature. Our measurements indicated that the emulsion shear in the injector nozzle shifted the emulsion droplet size distribution towards the smaller end resulting in a delay in the onset of micro-explosion. This delay in the onset of the micro-explosion is thought to be due to the decrease in the dispersed water coalescence rate which, in turn, increases the stability of the emulsion. The results also show that this delay in the onset of micro-explosion, and the temperature required for its onset, increased with injection pressure.

Comparison of NOx and Smoke Characteristics of Water-in-Oil Emulsion and Marine Diesel Oil in 400-kW Marine Generator Engine

“…The 3-phase emulsion is prepared using methods such as phase transfer, mechanical stirring and two-step emulsion. The two-step emulsified technology is widely used for O/W/O emulsions and has been reported in many studies [22][23][24][25]. A 2-phase oil/water (O/W) emulsified oil is first prepared using hydrophilic additives and then a 3-phase emulsion is formed using lipophilic surfactant.…”

Investigation of Puffing and Micro-Explosion of Water-in-Diesel Emulsion Spray Using Shadow Imaging

“…Based on the evidence that the injector nozzle shifts the size distribution of the dispersed phase towards smaller droplet sizes (discussed in the previous works [32,35]), only samples after the injector were used in each experiment.…”

“…A Span 80 (a lipophilic surfactant) with a hydrophilic-lipophilic balance (HLB) of 4.3 was used as the emulsifying agent to prepare 10% (v/v) water in diesel emulsion. A gravitational method [35][36][37] was used to characterize the stability of the emulsion. For this purpose, a mechanical stirrer running at 1000 rpm for 10 min was used to blend the emulsion, which was then stored in cylindrical tubs as shown in Figure 1.…”

“…An electronic fuel injection system (common rail) was used to spray and collect the injected samples, in order to characterize the emulsion's size distribution. The complete details for the setup, including the control of the injector opening and duration, can be found in the authors' previous work [32,35].…”

“…This algorithm automatically detects and measures the dispersed droplet size and number. The image processing sequence is discussed in detail in our previous work [32,35]. The equivalent diameter of each detected droplet was calculated based on the droplet's area.…”