An experimental study on evaporation, puffing, micro-explosion, and secondary breakup of multi-fuel blend droplet

Abstract

To mitigate the significant impact of CO₂ and other GHG on global warming and climate change, it is crucial to target one of the major sources of these emissions—fossil fuel-powered vehicles. These vehicles include cars, trucks, and buses, relying on internal combustion engines and are significant contributors to CO₂ emissions within the transportation sector. Although these vehicles are gradually being replaced by renewable energy and hybrid alternatives, they still hold a significant share of the market and vehicle fleet, making it essential to improve their efficiency and reduce emissions during this transition. Supported by advanced strategies, such as injection techniques—CRDI, PI and VIT, combustion technologies—HCCI, PCCI, LTC and DF, after treatment systems—SCR, DPF and EGR, conventional diesel fuel continues to be widely utilized due to its high energy density and superior fuel efficiency with ICEs. Blending diesel with alternative biofuels such as biodiesel and bio-alcohols, presents a promising approach for enhancing engine performance and reducing emissions. The study critically examines the potential of these alternative biofuels usability in ICEs, to enhance fuel atomization and address the challenges related to their integration into existing engine technologies. The study investigates the transient behaviours of microdroplets in alternative multi-fuel blends for ICEs with a focus on biodiesel and bio-alcohol blends to explore these behaviours impact on fuel-air mixing. Experiments were conducted through introducing single fuel, binary, and ternary fuel blend droplets in various environmental temperature using LDBOS. These experiments were performed at three high temperatures: LLPT, MLPT and HLPT. The experimental fuels included diesel, biodiesel, HVO, bio-alcohols (methanol, ethanol, and octanol), and their blends. The transient behaviours of these fuel droplets were recorded using DBIMP technique, capturing key phenomena such as evaporation, nucleation, puffing, micro-explosion, secondary breakup, and combustion. Key findings of the study include The evaporation rate of diesel-biodiesel blends was slightly lower than that of diesel-HVO blends, with pure diesel demonstrating the fastest evaporation rate.

The addition of biodiesel and HVO significantly reduced soot formation during combustion. Blends with a high diesel content are prone to ignite at high temperatures. In diesel-water emulsions, droplets exhibited more reactive behaviour, including rapid expansion and deformation at high temperatures. Blends of diesel/biodiesel/HVO with alcohols (methanol, ethanol, and octanol) showed enhanced puffing and micro-explosion phenomena intend to improve fuel-air mixing. The inclusion of water with more than 35% volume fraction, further intensified puffing and micro-explosion effects, particularly at higher temperatures. Aerated diesel showed shorter evaporation times with longer aeration durations, highlighting the influence of aeration on evaporation behaviour.

Overall, the study suggests that heating temperature has the most significant impact on fuel evaporation, puffing, micro-explosion, and combustion phenomena, followed by fuel composition and blending ratio. These findings provide important guidance for optimizing fuel formulations to enhance fuel atomization and fuel-air mixing, presenting a promising strategy for improving the performance of alternative multi-fuel blends in ICEs.