Search Results (6)

This study aims to investigate the structural, spectroscopic, and electronic properties of the synthetic missile fuel exo- and endo-tetrahydrodicyclopentadiene (THDCPD, JP-10) using density functional theory (DFT). It is to understand the dominance of the liquid exo-isomer (96%) of the jet fuel from the subtle differences between the isomers. The present DFT calculations reveal that the exo-isomer is 15.51 kJ/mol more stable than the endo-isomer, attributed to the flipping of the triangular ΔC8-C10-C9 ring in its norbornane skeleton. Calculated nuclear magnetic resonance (¹³C-NMR) and infrared (IR) spectra, validated by experimental data, reveal larger chemical shifts for junction carbons (C1/C2 and C3/C4) due to reduced electron shielding and show distinct vibrational patterns. Charge analysis indicates that all carbon atoms are negatively charged except for the C1/C2 carbons which are positively charged in both isomers. While overall IR spectra of the isomers appear similar, bands near 3000 cm⁻¹ correspond to distinctly different vibrational modes. The exo-isomer’s electronic structure features a more delocalized HOMO and a larger HOMO-LUMO gap (7.63 eV) than the endo-isomer (7.37 eV). All such differences contribute to the properties of exo-THDCPD and, therefore, why the exo-isomer dominates JP-10 fuel. Full article

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. Full article

With growing interest in sustainable civil supersonic and hypersonic aviation, there is a need to model the combustion of alternative, sustainable jet fuels. This work presents numerical simulations of several related phenomena, including laminar flames, ignition, and spray flames. Two conventional jet fuels, Jet A and JP-5, and two alternative jet fuels, C1 and C5, are targeted. The laminar burning velocities of these fuels are predicted using skeletal and detailed reaction mechanisms. The ignition delay times are predicted in the context of dual-mode ramjet engines. Large Eddy Simulations (LES) of spray combustion in an aeroengine are carried out to investigate how the different thermodynamic and chemical properties of alternative fuels lead to different emergent behavior. A novel set of thermodynamic correlations are developed for the spray model. The laminar burning velocity predictions are normalized by heat of combustion to reveal a more distinct fuel trend, with C1 burning slowest and C5 fastest. The ignition results highlight the contributions of the Negative Temperature Coefficient (NTC) effect, equivalence ratio, and hydrogen enrichment in determining ignition time scales in dual-mode ramjet engines. The spray results reveal that the volatile alternative jet fuels have short penetration depths and that the flame of the most chemically divergent fuel (C1) stabilizes relatively close to the spray. Full article

The aviation sector is facing a massive change in terms of replacing the currently used fossil jet fuels (Jet A, JP5, etc.) with non-fossil jet fuels from sustainable feedstocks. This involves several challenges and, among them, we have the fundamental issue of current jet engines being developed for the existing fossil jet fuels. To facilitate such a transformation, we need to investigate the sensitivity of jet engines to other fuels, having a wider range of thermophysical specifications. The combustion process is particularly important and difficult to characterize with respect to fuel characteristics. In this study, we examine premixed and pre-vaporized combustion of dodecane, Jet A, and a synthetic test fuel, C1, based on the alcohol-to-jet (ATJ) certified pathway behind an equilateral bluff-body flameholder, spray combustion of Jet A and C1 in a laboratory combustor, and spray combustion of Jet A and C1 in a single-sector model of a helicopter engine by means of numerical simulations. A finite rate chemistry (FRC) large eddy simulation (LES) approach is adopted and used together with small comprehensive reaction mechanisms of around 300 reversible reactions. Comparison with experimental data is performed for the bluff-body flameholder and laboratory combustor configurations. Good agreement is generally observed, and small to marginal differences in combustion behavior are observed between the different fuels. Full article

An Al/JP-10/oleic acid nanofluid fuel system has demonstrated potential in advanced combustion for aviation turbine engines. To improve the energy density of nanofluid fuel, a higher Al concentration requirement needs to be met. Correspondingly, a higher surfactant oleic acid concentration is required to maintain better dispersion stability. The increment of Al and oleic acid concentrations results in more frequent microexplosions, but a slower evaporation rate. Therefore, this paper proposes to deeply understand the contradiction of the concentration effect on the stability, physical properties, evaporation and microexplosion characteristics and obtain the best Al and oleic acid concentrations to maintain the most suitable comprehensive performance. Experiments on the stability, physical properties, evaporation and microexplosion characteristics were conducted, respectively. The analysis and discussion were then made to reveal the Al and oleic acid concentration effect on the stability, physical properties, evaporation and microexplosion characteristics. The results show that the optimum mass ratio of Al:oleic acid is 1:2 for the nanofluid fuels with Al concentrations of 2.5 wt.% or below, 1:2.5 for 5.0 wt.% or above to obtain the best stability. The physical properties of the nanofluid fuels such as density, surface tension and viscosity are linear, quartic and quadratic functions of Al concentration, respectively, relating to the internal flow and microexplosion of fuel droplets. With increasing oleic acid and Al concentration, the evaporation rates reduced, and the microexplosions became more frequent and intense. At a high ambient temperature of 600 °C, the evaporation rates were kept almost equivalent for JP-10, JP-10/oleic acid, and Al/JP-10/oleic acid fuels. It was found that the increment of ambient temperature can compensate for the reduction of the evaporation rate owing to the addition of oleic acid and Al nanoparticles, improving the evaporation and microexplosion performance. Full article

Diversification of energy sources is a key task for decreasing environmental impacts and global emission of gases. JP-8, a fuel derived from natural gas, coal, biomass, and waste plastics, is a bright prospect. JP-8 is considered a multi-source multi-purpose fuel, with several applications. A preliminary characterization of the JP-8 injection rate and injection quantity behavior was investigated based on the high-pressure common rail injection system used in a heavy-duty engine. According to the spill injection and injection pressure, a trade-off trend between injection rate and injection quantity was observed. As expected, pilot injection of JP-8 aviation fuel and diesel fuel affects the spray quantity and injection evolution of the subsequent operation without pilot injection. The difference in spilling between diesel and JP-8 aviation fuel is greater than the difference in injection amount per time; in the process of controlling the injector solenoid through ECU (Electric Control Units), the oil pressure valve and the needle valve operate to a higher extent in order to maintain the diesel fuel’s injection quantity volume. It was found that the total injection quantity was decreased by adding 20% pilot injection duration. Because the pilot injection quantity causes solenoid response, loss and needle lift stroke friction loss. Full article