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Adding water to fuel droplets is known to lead to puffing and micro-explosion. Puffing and micro-explosion lead to a rapid increase in the liquid fuel surface area. This, in turn, leads to an increase in the fuel evaporation rate and the formation of a homogeneous fuel vapor/air mixture. The latter is important for improving the efficiency of combustion technologies, including those used in internal combustion engines. The effects produced by puffing and micro-explosion lead to a reduction in fuel consumption, improved fuel/air mixing, and a reduction in harmful emissions. The contributions of puffing and micro-explosion to fire extinguishing have also been discussed in many papers. In this paper, we review the state of the art in the investigation of composite droplet micro-explosion and discuss the sufficient conditions for the start of puffing/micro-explosion as well as child droplet characteristics.

Water-in-diesel emulsions potentially favor the occurrence of micro-explosions when exposed to elevated temperatures, thereby improving the mixing of fuels with the ambient gas. The distributions and sizes of both spray and dispersed water droplets have a significant effect on puffing and micro-explosion behavior. Although the injection pressure is likely to alter the properties of emulsions, this effect on the spray flow puffing and micro-explosion has not been reported. To investigate this, we injected a fuel spray using a microsyringe needle into a high-temperature environment to investigate the droplets’ behavior. Injection pressures were varied at 10% v/v water content, the samples were imaged using a digital microscope, and the dispersed droplet size distributions were extracted using a purpose-built image processing algorithm. A high-speed camera coupled with a long-distance microscope objective was then used to capture the emulsion spray droplets. Our measurements indicated that the secondary atomization was significantly affected by the injection pressure which reduced the dispersed droplet size and hence caused a delay in puffing. At high injection pressure (500, 1000, and 1500 bar), the water was evaporated during the spray and although there was not enough droplet residence time, puffing and micro-explosion were clearly observed. This study suggests that high injection pressures have a detrimental effect on the secondary atomization of water-in-diesel emulsions.

The present experiment was conducted by executing detailed tests on performance, combustion, and emission characteristics to prove that the Nerium biodiesel emulsified fuel can be an eco-friendly fuel. The emulsified biodiesel was formed by mixing with a small proportion of water in the limits of 5%, 10%, and 15% by volume. This study also assessed the stability of different emulsified blends. The properties were tested according to ASTM requirements. The blend of 60% diesel, 20% biodiesel, 15% water, and 5% surfactant showed the higher brake thermal efficiency and in-cylinder pressure by 13.72% and 12.6%, respectively, when related to base fuel. Also, carbon monoxide, oxides of nitrogen, opacity of smoke and hydrocarbon emission of the above blend decreased by 42.87%, 6.5%, 12.96%, and 31.94%, respectively, when related to base fuel. This can be attributed due to the micro-explosion and availability of the oxygen content in the fuel. The results noticed a significant improvement and advantage of using the eco-friendly emulsified fuel in traditional engines without any modifications. Micro-explosion during combustion stage guaranteed a reduction in emission of nitrogen oxides (NOx).Graphic abstract

The development of high-energy-density fuels is critical for advancing energy conversion technologies in propulsion and energy systems. Although nanofluid fuels have shown promise in enhancing combustion performance, the fundamental mechanisms governing high-solid-content systems—particularly their dynamic combustion behavior, micro-explosion processes, and associated energy release—remain insufficiently explored. This study systematically examines boron/JP-10 nanoslurry fuel droplets with high boron loadings (30 wt%–50 wt%) using micro highspeed imaging, two-dimensional temperature field measurements, and radiation spectroscopy. Results reveal that boron concentration critically affects combustion dynamics: increasing boron loading intensifies micro-explosions, which raises the flame temperature and accelerates the overall energy release. However, there is a concentration threshold; beyond this point, excessive particle loading promotes agglomeration, suppresses micro-explosions, and reduces both combustion efficiency and energy release. Spectral analysis confirms active participation of boron via BO2 radical emission. The residue morphology transitions from porous structures to dense shells with increasing concentration. This work provides new fundamental insights into the multiphase combustion mechanisms of high-energy-density slurry fuels and contributes to the design of advanced fuels for efficient energy conversion.

Aluminum/tetrahydrodicyclopentadiene/oleic acid (Al/JP-10/OA) nanofluid fuel is considered a potential fuel for aircraft powered by aviation turbine engines. However, an optimized formula for an Al/JP-10/OA system inducing a secondary atomization and micro-explosion effect and improving the burning performance needs to be developed. With this aim, in this work, the combustion characteristics of pure JP-10, JP-10/OA, JP-10/Al, and Al/JP-10/OA were experimentally tested, and a comparative analysis was conducted. Specifically, the influence of the surfactant and nanoparticle concentrations on the combustion characteristics of Al/JP-10/OA nanofluid fuel, including the flame structure, the flame temperature, the burning rate, the secondary atomization and micro-explosion effect, etc., were evaluated in detail. The results demonstrate that the addition of OA surfactant and Al nanoparticles had a significant effect on the burning rate of fuel droplets. The OA had an inhibition effect, while the Al nanoparticles had a promotion effect. As both OA and Al nanoparticles were added to the JP-10, the synergetic effect had to be considered. At the optimum ratio of OA to Al for the best suspension stability, there is a critical Al concentration of 1.0 wt.% from promotion to inhibition with increases in the Al concentration. The addition of OA and Al nanoparticles induced the secondary atomization and micro-explosion, resulting in an unsteady combustion and chaotic flame structure. The transient flame temperature of hundreds of Kelvins increased, the high-temperature flame zone widened, and thus, the energy release was elevated. Therefore, the combustion performance and energy release of Al/JP-10/OA nanofluid fuel can be improved through the secondary atomization and micro-explosion effect induced by the surfactant and nanoparticles.

Efficient and harmless disposal of multi-source organic liquid waste is a key requirement in current environmental protection. Herein, we employ high-temperature tube furnaces, small-scale rotary kilns, and industrial rotary kilns as test platforms, focusing on high-temperature conditions (>1200 °C) in existing industrial kilns. Systematic studies on combustion characteristics, pollutant emission laws, and disposal adaptability were conducted. We aim to clarify the intrinsic correlations between co-incineration behaviors, pollutant generation, and disposal feasibility for the co-incineration of multi-source organic liquid waste in cement kilns. The results demonstrate significant interaction effects during the co-incineration of multi-source organic liquids, which reduces combustion energy consumption and improves operational safety. The “micro-explosion” effect generated by high-temperature incineration is the key to regulating pollutant emissions, with CO emissions of only 6.71%. Tests on small and industrial rotary kilns indicate that co-disposal of liquid waste in cement kilns does not affect the stable operation of the kiln or the quality of the cement clinker, and pollutant emissions meet industrial standards. This work can provide a scientific basis and technical support for large-scale, efficient, and clean disposal of organic liquid waste in industrial cement kilns.

The evaporation, autoignition and micro-explosion characteristics of RP-3 kerosene droplets under sub-atmospheric pressure (0.2–1.0 bar) and elevated temperature (473–1023 K) were experimentally investigated using high-speed camera technology. The results showed that the droplet evaporation rate increased monotonically with increasing temperature and pressure under 573–873 K and 0.2–1.0 bar. The decrease of temperature and pressure was obviously detrimental to the successful autoignition of droplets and increased the ignition delay time. Autoignitions at 0.2 bar were very difficult and required an ambient temperature of at least 973 K, which was about 150 K higher than the minimum ignition temperature at 1.0 bar. Sub-atmospheric pressure environment significantly inhibits the formation of soot particle clusters during the autoignition of droplet. Reducing pressure was also discovered to reduce the likelihood of micro-explosions at 673, 773 and 823 K but increase the bubble growth rate and droplet breakage intensity. Strong micro-explosions with droplet breakage time close to 1 ms were observed at 0.6 bar and 773/823 K, showing the characteristic of bubble inertia control growth.

The present study investigates the combustion characteristics of the multicomponent diesel-water (D-W) emulsion fuel droplets. The stable blends obtained by using Surfactant, Span-80 (s) and three different fuels viz., WD1 (D-95%, W-3%, S-2%), WD2 (D-94%, W-4%, S-2%) and WD3 (D-96%, W-3%, S-1%) are subjected to the pendant mode of droplet combustion in the ambient conditions. The blend's stability depends on surfactant and water compositions. WD1 exhibited a higher viscosity W/s ≥ 1 at near-boiling point of the dispersed fluid. The higher viscosity droplets resulted in fewer secondary atomization. WD3 with lower viscosity (W/s >1.5) exhibited multiple cycles of the micro-explosion events. The cycles of micro-explosion depend on water to surfactant concentration. The blend with lesser surfactant exhibited the lesser cycles of explosion events. The regression rate of the droplets was fitted using d2-law. WD1 possesses the least burn time. The vapors of low volatile fluid, i.e., water vapor were trapped inside emulsion the droplets. Upon receiving the constant heat from flame surface, the surface of the droplets gets highly corrugated due to the capillary oscillations. Subsequently, the trapped bubbles of the less volatile fluid are ejected out as the daughter droplets. These ejections are more predominant in higher surfactant concentrations. The ejections frequency reduces with an increase in water %. This enabled the rapid burning of the droplet when compared to base fuel combustion.

The environmental, economic, and energy problems of the modern world motivate the development of alternative fuel technologies. Multifuel technology can help reduce the carbon footprint and waste from the raw materials sector as well as slow down the depletion of energy resources. However, there are limitations to the active use of multifuel mixtures in real power plants and engines because they are difficult to spray in combustion chambers and require secondary atomization. Droplet micro-explosion seems the most promising secondary atomization technology in terms of its integral characteristics. This review paper outlines the most interesting approaches to modeling micro-explosions using in-house computer codes and commercial software packages. A physical model of a droplet micro-explosion based on experimental data was analyzed to highlight the schemes and mathematical expressions describing the critical conditions of parent droplet atomization. Approaches are presented that can predict the number, sizes, velocities, and trajectories of emerging child droplets. We also list the empirical data necessary for developing advanced fragmentation models. Finally, we outline the main growth areas for micro-explosion models catering for the needs of spray technology.

To address the problems of the reduced evaporation rate and increased ignition time of kerosene droplets at sub-atmospheric pressures and high temperatures, boron and ethanol/water were selected as additives to be blended with RP-3 kerosene, respectively. The effects of different types of blended fuels on the evaporation, micro-explosion, and spontaneous ignition characteristics of RP-3 kerosene droplets were tested and compared using an independently designed, high-temperature, controlled-pressure experimental droplet system. A low-pressure environment (0.4 bar) promoted the high-intensity micro-explosion of RP-3/B and RP-3/water/ethanol droplets while reducing the number of puffing events. A comparative study of RP-3/B and RP-3/ethanol/water found that ethanol/water blended fuels had a higher micro-explosion intensity (1000–10,000 vs. 0.2–15 mm/s) and shorter droplet lifetimes and self-ignition times at low pressure. The 30%water fuel (30 vol.%water in water/ethanol sub-droplet) had the shortest ignition/breakup time, with an ignition time of 0.5715 s at 0.8 bar, 26.92% shorter than RP-3’s 0.782 s. This 30%water fuel mixture can increase the release rate of combustible vapors prior to ignition by inducing puffing and micro-explosions at high temperatures.