Experimental investigation on droplet burning characteristics of diesel-benzyl azides blend

- Burning characteristics of diesel-benzyl azides blend droplet are studied.
- Micro-explosion shortens combustion duration for smaller droplet sizes.
- Liquid-phase reaction of benzyl azides improves the burning rate of droplets.
- Increasing mass fraction of benzyl azides strengthens the soot generation propensity.
- Ambient oxygen concentration and initial diameter affect combustion characteristics.

In this work, the droplet burning characteristics of neat benzyl azides, diesel-benzyl azides blends (10%, 30%, 50% of benzyl azides (wt.)) and diesel fuel were investigated under atmospheric pressure. The ambient temperature around the flat-flame burner is about 1123 K. The initial droplet temperature is about 300 K. The effects of ambient oxygen concentration (14%, 21% and 30%) and initial droplet diameter (∼257 μm and ∼456 μm) on the burning characteristics were also studied. Experiments were carried out using the droplet free falling technique. A CCD camera with a micro lens was used to collect droplet photos, through which the droplet burning rate and flame size were deduced. A strobe light which could freeze the droplet visually was also used to collect ignition delay and combustion duration. The flat-flame burner manipulated by varying the composition of the premixed gas consisting of propane, oxygen, and air was used to provide combustion environment. The results show that the addition of benzyl azides not only increases the burning rate but also causes micro-explosion before the end of the flame because of the occurrence of liquid-phase reaction. With the increase of benzyl azides mass fraction, the ignition delay decreases, the combustion duration first increases and then decreases. Furthermore, due to the faster evaporation rate of benzyl azides, the droplet flame sizes increase with the benzyl azides mass fraction increasing during burning. However, the diesel-benzyl azides blend has stronger sooting propensity than diesel. Meanwhile, the ambient oxygen concentration and droplet initial diameter have important effects on the burning characteristics of diesel-benzyl azides droplet.