Properties effect of blending fischer-tropsch aviation fuel on spray performances
Introduction
Increasing concern with respect to the growing energy demand and environmental protection drive the need for clean, alternative energy. The transportation industry, especially commercial aviation business, is playing an increasingly important role in energy consumption. According to forecast, 1950 freighter aircraft, of which 730 new build freighter aircraft will be needed by 2036 [1]. Gases and particles emitted by the aircraft could alter the concentration of atmospheric greenhouse gases including CO2, O3, CH4 and water vapor [2]. As a result, the interest in alternative aviation fuel is growing dramatically. Fuel derived from the fischer-tropsch process, owing to the near absence of aromatic and nitrogen, sulfur and other contents which could cause environmental damage in the composition, is treated as a possible alternative fuel in the near future. However, in order to be used as drop-in fuel, the characteristics of FT fuels have to meet the demanding requirements of the gas turbine engines for reliability and safety. In this situation, properties of FT fuel need to be thoroughly studied. Fully Synthetic Jet Fuel (FSJF), a coal-to-liquid fuel produced by Sasol, is known as the first fuel that can pass all the ASTM D7566 requirements. Studies on performances of FSJF have been carried out [[3], [4], [5]]. The results show that the properties and characteristics of Sasol FSJF fall within the experience of conventional jet fuels from petroleum. Zhao et al. [6] analyzed the atomization performance and thermogravimetric of coal-based fischer-tropsch synthetic fuel made in China, they reported that the average sauter mean diameter (SMD) and Burnout index of coal-based synthetic fuel are 9.4% smaller and 9.0% greater than those of RP-3 with a difference of approximately. Yang et al. [7] also investigated basic combustion performances and range of Chinese FT alternative fuel and reported that the FT fuel’ s lower density and higher calorific value lead to its range shortened by 2.1%. However, more researches needed to be done to thoroughly analysis the performances of Chinese FT fuel.
It is known that the combustion performance of fuels, which has a great influence on the performance of aero engines, is mostly decided by the spray characteristics of fuels. Macroscopic spray characteristics such as spray cone angle and liquid length determine the distribution of fuel in the combustion chamber, microscopic spray characteristics such as SMD and velocity of droplets have a significant impact on the combustion characteristics of the fuel. Differences of physical properties of fuels have an important effect on the atomization performances. Therefore, it is necessary to thoroughly understand how the physical properties effect the atomization characteristics. Studies on atomization have been carried out. Saha et al. [8] studied the breakup and coalescence characteristics of a hollow cone swirling spray, the effects of Reynolds number and Weber number in the liquid breakup regimes were presented in their study. Sivakumar et al. [9] investigated the atomization characteristics of aviation biofuel from a simplex swirl atomizer, they reported that the trend of SMD variation with axial distance is influenced by the atomizer flow conditions. Gan et al. [10] tested the effect of linear alkane C17, C18 on spray characteristics of jet fuel, the results show that a narrowed spray cone angle and decreased SMD were caused by additional linear alkanes. Kannaiyan et al. [[11], [12], [13]]also did considerable research on the atomization performances of synthetic alternative fuels. Comparing to the entire combustion chamber with a complex flow field, changes in fuel properties has a greater effect near the nozzle exit. However, far too little attention has been paid to discuss the differences of spray field near the nozzle exit caused by the different physical performances of FT fuel, especially flow details of the reflux zoon downstream the nozzle exit.
The objective of this study is to better understand the details of the atomization field of FT fuel near the nozzle exit and to get more insights information on the influence of fuel properties on spray reflux zoon. For this reason, this paper focuses on the macroscopic and microscopic spray characteristics of FT fuel near the nozzle exit, and attempt to relate fuel properties to their atomization performance through empirical formulas of SMD, cone angle and liquid length. Some researchers have been reported that the atomization performances of different fuels is very similar under high injection pressure [6,10], so the main objective of this study is to observe the differences of atomization performances between different fuels under low injection pressure.
Section snippets
Experimental details
Chemical components of FT fuel are different from those of conventional jet fuel due to the differences in the feedstock and refining process. As a result, both the chemical and physical performances could be different between FT fuel and conventional jet fuel. This study measured physical properties that may affect atomization performance such as density, viscosity and surface tension to help figure out how chemical components influence spray performances.
Fuel composition
Chemical compositions of RP-3 and FT fuel were investigated and shown in Fig. 4. Fig. 4 (a) classified the main components of RP-3 and FT fuel. About 70% of RP-3 is made up of normal straight chain (36.1%) and branched chain alkanes (33.5%), the remaining 30% are consisted by cyclo-paraffins (10.0%), aromatic (16.1%) and other components including polyaromatics. In contrast, the content of n-paraffins (76.8%) and iso-paraffins (22.9%) in FT fuel is close to 99% due to the characteristics of the
Conclusions
This work focus on the differences of macroscopic and microscopic spray performances between FT fuel and Chinese jet fuel RP-3 in a pressure swirl nozzle. The photographic measurement results show that both the maximum differences of the liquid length and the cone angle between fuels appear at the injection pressure of 0.1 MPa, where the liquid length of FT is 18.2% lower and the cone angle of FT fuel is 6.75% higher than those of RP-3, respectively. The results of the PDA measurement show a
Acknowledgement
This paper was supported by National Key Research and Development Program-International Cooperation Innovation-China (2016YFE0120100)
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