An experimental study on droplet-scale combustion and atomization behavior in pure ethanol, methanol, and trimethyl borate, and their blends

Abstract

The combustion and atomization behavior of pure ethanol (EtOH), methanol (MeOH) and trimethyl borate (TMB) fuels and their blends prepared at 20 wt%, 40 wt%, 60 wt% and 80 wt% ratios were determined by processing videographs recorded with a high-speed camera and temperature data recorded with a thermal camera during droplet-scale combustion experiments performed at atmospheric pressure. EtOH and MeOH are good alternatives for transport due to their high oxygen content and relatively short carbon chains. TMB, an organoboron derivative in the liquid phase, is unique to creating a low-carbon emission and high-energy alternative fuel blend with boron, oxygen, and short carbon chains. This study focuses on the preparation of EtOH, MeOH, and TMB fuels and homogenized fuel mixtures with high energy values and the characterization of their combustion behavior. The experiments were carried out by suspending ethanol-trimethy borate (EtOH-TMB) and methanol-trimethyl borate (MeOH-TMB) fuel droplets on SiC wire and igniting them with an electrode producing an arc of 1 ms duration at 20 ms intervals with 6 kV energy. The results showed that EtOH and TMB formed a homogenized fuel mixture at all mixing ratios and the largest and most homogeneous green luminescence flame envelopes (depending on boron oxidation) were formed, indicating BO2 formation in almost all fuel mixtures. On the other hand, the droplets of MeOH-TMB fuel mixtures containing 20 wt%, 40 wt%, and 60 wt% MeOH exhibited the most favorable trend to the D2-law of diameter reduction during combustion. EtOH-TMB fuel droplets containing 60 wt% TMB exhibited the highest maximum flame temperature of 631 K. In this study, it has been shown that new-generation hybrid transportation fuels with no phase separation, low ignition delay times despite increased oxygen content, and high calorific value can be produced with hybrid fuel blends to be formed with TMB and alcohols. The results obtained will shed light on the literature for the solution to the problematic combustion characteristics of boron, which is tried to be used in many areas of the transportation industry.