Experimental Study on Evaporation and Micro-Explosion Characteristics of Ethanol and Diesel Blended Droplets
Abstract
:1. Introduction
2. Experimental Device and Image Processing Method
2.1. Evaporation Device
2.2. Image Processing Method
2.3. Fuel Preparation and Physical Properties
3. Results and Discussion
3.1. Evaporation Sequence Diagram of Mixed Droplets
3.1.1. Evaporation Sequence of the DE20 Droplet
3.1.2. Evaporation Sequence of the DE40 Droplet
3.1.3. Evaporation Sequence of the DE60 Droplet
3.1.4. Evaporation Sequence of the DE80 Droplet
3.2. Evaporation Mode
3.3. The Influence of Mix Proportion on the Droplet Diameter
3.4. Expansion Intensity and Crushing Intensity
3.5. Time Percentage of Different Evaporation Stages
4. Conclusions
- (1)
- With the increase in ethanol blending ratio in mixed droplets (the proportion of ethanol gradually increased from 20% to 80%), the encapsulation mode of droplets changed from water-in-oil mode to oil-in-water mode. In water-in-oil mode, due to the high content of heavy components, the oil film directly covered the surface of the droplet, and the light components vaporized inside the droplet after they absorbed heat, and then gathered inside the droplet, resulting in ejection and micro-explosion. In the early stage of oil-in-water mixed droplets, light components were wrapped on the surface of the droplet, which needed to undergo evaporation for a period of time and then turned into water-in-oil mixed droplet. The droplet diameter changed in this stage, satisfying the d2 law.
- (2)
- The evaporation of droplets was divided into the following four modes: strong micro-explosion mode, ejection mode, exocytosis mode, and tensile crushing mode, and the explosion intensity decreased in turn.
- (3)
- The vapor cloud phenomenon was found in the evaporation process of the DE60 droplet, which was due to the high evaporation rate on the droplet surface, which led to the mixture of vapor and ambient gas, and the non-isothermal condensation phenomenon of a droplet under the condition of uneven heating.
- (4)
- Notably, our findings reveal the positive impact of increased ethanol content in reducing emissions such as particulates and NOx from diesel engines. However, as highlighted in the research by Nord, A.J., J.T. Hwang, and W.F. Northrop [50], while e-diesel can reduce particulate emissions, there remains controversy over its effects on NOx, CO, and HC emissions. Additionally, the low flash point of e-diesel could pose safety challenges.
- (5)
- Although diesel is compositionally complex, its evaporation process at 723 K can be regarded as the evaporation of a single-component droplet, satisfying the d2 law. The evaporation process of ethanol–diesel mixed droplets is divided into three phases, as follows: instantaneous heating, fluctuating evaporation, and equilibrium evaporation stages. During the fluctuating evaporation stage, droplets can produce ejections and micro-explosions of various intensities. The number and velocity of secondary droplets are positively correlated with the expansion and micro-explosion intensities of the droplets; the greater the intensity, the more numerous the secondary droplets.
- (6)
- Based on the experimental phenomena and comprehensive analysis, a model for the expansion and crushing intensities of mixed fuels was proposed that better conforms to actual laws. This model was used to calculate the expansion and crushing intensities of ethanol–diesel mixed droplets at different blend ratios. With the increase in ethanol blend ratio, both expansion and crushing intensities first increase and then decrease. This trend is consistent with the phenomena observed experimentally, where the expansion and crushing intensities were highest for the DE40 droplets.
- (7)
- Combining our experiments with those of Chen, Chan-Cheng, and Horng-Jang Liaw [51] comparing typical diesel fuel, we found that ethanol has a significantly higher spontaneous combustion temperature (AIT) of 368.8 °C, which significantly affects the ignition and combustion process under typical engine operating conditions. This higher AIT indicates that the use of ethanol–diesel mixtures may require the adjustment of engine settings or additional preheating measures, to ensure efficient and safe combustion under a variety of environmental conditions. Therefore, the development and optimization of ethanol–diesel mixtures as an alternative fuel requires not only consideration of its environmental properties, but also evaluation of its feasibility and safety in practical applications.
- (8)
- There is a clear positive correlation between the high microburst intensity observed in this study and the evaporation rate of droplets. Droplets with higher micro-explosion intensity promote more uniform and complete combustion by increasing the contact area between fuel and air. This improved combustion efficiency significantly reduces engine emissions of solid particles and unburned hydrocarbons, making it environmentally friendly. Particularly in internal combustion engines using diesel–ethanol blends, ethanol’s high oxygen content helps to reduce emissions of harmful gases such as nitrogen oxides (NOx), as the additional oxygen molecules promote a more complete combustion reaction. Future research will use techniques such as spectral analysis to quantitatively analyze this relationship to verify the specific impact between evaporation rate and environmental emissions.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Composition of Fuel Mixture (Volume Basis) | Designated Nomenclature |
---|---|
20% ethanol, 78% diesel, 2% n-decanol | DE20 |
40% ethanol, 58% diesel, 2% n-decanol | DE40 |
60% ethanol, 38% diesel, 2% n-decanol | DE60 |
80% ethanol, 18% diesel, 2% n-decanol | DE80 |
Properties | Diesel | Ethanol | DE20 | DE40 | DE60 | DE80 |
---|---|---|---|---|---|---|
Density (20 °C) [kg/L] | 0.822 | 0.789 | 0.816 | 0.811 | 0.805 | 0.799 |
Viscosity (20 °C) [mm2/s] | 2.93 | 1.20 | 1.95 | 1.82 | 1.72 | 1.63 |
Surface tension (mN/m) | 27.84 | 22.32 | 23.41 | 23.25 | 23.09 | 22.98 |
Boiling point (K) | 550–650 | 351 | — | — | — | — |
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Zhang, Y.; Meng, K.; Bao, L.; Lin, Q.; Pavlova, S. Experimental Study on Evaporation and Micro-Explosion Characteristics of Ethanol and Diesel Blended Droplets. Atmosphere 2024, 15, 604. https://doi.org/10.3390/atmos15050604
Zhang Y, Meng K, Bao L, Lin Q, Pavlova S. Experimental Study on Evaporation and Micro-Explosion Characteristics of Ethanol and Diesel Blended Droplets. Atmosphere. 2024; 15(5):604. https://doi.org/10.3390/atmos15050604
Chicago/Turabian StyleZhang, Yixuan, Kesheng Meng, Lin Bao, Qizhao Lin, and Svitlana Pavlova. 2024. "Experimental Study on Evaporation and Micro-Explosion Characteristics of Ethanol and Diesel Blended Droplets" Atmosphere 15, no. 5: 604. https://doi.org/10.3390/atmos15050604