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Addai, Emmanuel Kwasi; Gabel, Dieter; Ali, Haider; Krause, Ulrich
doi: 10.1080/00102202.2016.1211447pmid: N/A
Investigation of the ignition behavior (minimum ignition temperature [MIT]) of dusts, gases, or solvents and their mixtures has been undertaken by performing a series of tests in the modified Godbert–Greenwald furnace. Four flammable gases (methane, propane, ethanol, and isopropanol) as well as three combustible dusts (starch, lycopodium, and toner) were used as materials. For the dusts alone test, the experimental protocol was in accordance with the European standard EN 50281-2-1, whereas for the gases, solvent vapors, and mixtures of these with the dusts, this protocol had to be modified slightly. The experimental results demonstrate the significant decrease of the MIT of either gas, solvent, or dust and an increase in the explosion likelihood when a small amount dust, which is either below the minimum explosion concentration or not ignitable itself at the given temperature, are admixed with gas or solvent and vice versa. For example, the MIT of methane decrease from 600°C to 585°C when a small amount of starch was added. This hybrid MIT further decreased to 490°C when a third component (ethanol) was added. The same effect was noticed when a small amount of gas was added to a dust; for example, toner with a MIT of 460°C decreases to 450°C when a small amount of ethanol was added, which further decreased to 430°C when a third component (propane) was added. The result also confirm that an explosion is possible for a process or a system where hybrid mixtures are generated even if the temperature is below the MIT of a single substance and, hence, the MIT of hybrid mixtures cannot be predicted by simply overlapping the effects of the single dust, gas, or solvent.
Dagaut, Philippe; Karsenty, Florent; Dayma, Guillaume; Serinyel, Zeynep
doi: 10.1080/00102202.2016.1212543pmid: N/A
The interest for synthetic and/or bio-derived jet fuels is increasing with the aim of reducing air transportation dependence on fossil fuels, soot emissions, and carbon footprint. Jet fuels can be produced through Fischer–Tropsch synthesis of paraffins followed by post-processing or blending to meet jet fuel specifications. Synthetic jet fuels mainly contain n-alkanes, iso-alkanes, and cyclo-alkanes, with possible aromatic fractions. The aim of this work is to study the kinetics of oxidation of gas-to-liquid (GtL) and coal-to-liquid (CtL) alternative jet fuels and representative surrogates in a jet-stirred reactor (JSR) operating under the same conditions of temperature, pressure, and equivalence ratio. To experimentally represent the selected synthetic jet fuels, we have designed surrogates consisting of 3–5 representative species. We experimentally studied the oxidation of these representative mixtures (n-decane, iso-octane, and decalin for GtL; n-decane, iso-octane, n-propylcyclohexane, decalin, and n-propylbenzene for CtL), a 100% GtL, and a 100% CtL in a JSR at 10 atm and an equivalence ratio φ = 1. A detailed kinetic reaction mechanism (2430 species versus 10,962 reversible reactions) and model fuels (4–7 components) were developed and validated by comparison with experimental results.
doi: 10.1080/00102202.2016.1212538pmid: N/A
The aim of this work is to study the effects of a multi-source ignition in a wide energy range on a two-phase mixture explosion composed of agricultural dusts with a gaseous fuel (methane or propane) and, more particularly, the pressure history inside a partitioned vessel. The initiation is introduced in the form of an increase of internal energy and a calculation methodology, which interestingly in the field of risk assessment is used to simulate the transmission of the explosion from one compartment to another adjacent compartment by means of the hot flow through the shared orifice and finally to generalize this methodology to a complex multi-partitioned structure. The basic characteristics of the model have been developed for the ignition and the combustion of dust suspensions and adapted to hybrid mixtures with appropriate parameters linked to simplified kinetics. A simple representation of the combustion phenomena based on energy transfers and the action of specific molecular species is presented. The model allows the study of the influence of various parameters, such as the dust or the gas concentration, the different ignition energies and their locations, and the size of the inner openings or the vent areas. The theoretical results have been compared with many data available in the literature and indicate correct preliminary tendencies.
Mokrani, Nabil; Rudz, Steve; Gillard, Philippe
doi: 10.1080/00102202.2016.1211856pmid: N/A
Ignition using laser breakdown of n-decane/air mixtures was investigated to highlight the influence of argon, moisture, concentration, and focal length on laser ignition probabilities. The effect of fuel impurities on minimum ignition energy (MIE) was also investigated. Characterization was performed using a Q-switched Nd-YAG laser (1064 nm) with a cylindrical vessel at a fixed temperature of 347 K and atmospheric pressure. The ignition probabilities obtained depended on the concentration of argon and water present in the combustion mixture. Results showed that Ar and H2O play a significant role in the breakdown process inducing ignition. MIE was determined for pure n-decane 99% and compared with the results of an impure n-decane 94% tested in a previous study. Finally, ignition delay time measured by recording photodiode signals and spectroscopic analysis was used to characterize ignition of the studied reactive mixtures as a function of different equivalence ratios.
Weinberg, Noam; Greenberg, J. Barry
doi: 10.1080/00102202.2016.1211858pmid: N/A
A laminar jet spray diffusion flame is analyzed mathematically for the first time using an extension of classical similarity solutions for gaseous jet flames. The analysis enables a comparison to be drawn between conditions for flame stability or flame blow-out for purely gaseous flames and for spray flames. It is found that, in contrast to the Schmidt number criteria relevant to gas flames, spray-related parameters also play a critical role in determining potential flame scenarios. Excellent qualitative agreement for lift-off height is found when comparing predictions of the theory and independent experimental evidence from the literature.
Mansouri, Zakaria; Aouissi, Mokhtar; Boushaki, Toufik
doi: 10.1080/00102202.2016.1211888pmid: N/A
Double helical precessing vortex core (PVC) and its interaction with premixed propane flame in a swirl-stabilized burner is studied numerically. The model burner is operated under atmospheric pressure, swirl number Sn = 1.05 and equivalence ratio Φ = 0.5. Turbulence-chemistry interaction is treated using detached eddy simulation (DES) turbulence model, and finite-rate/eddy dissipation model (FR/EDM) in combination with a 3-step reduced mechanism. The flow field is well captured by DES and the premixed flame is well reproduced by FR/EDM. Dominant strong vortices are detected in the shear layer of the inner recirculation zone, and secondary outer vortices are found in the combustion chamber corners. Temperature and reaction zone maps reveal that the flame is mainly stabilized in the inner shear layer. Q-criterion is used to visualize the 3D behavior of the flow. It is found that the unsteady flow contains a large-scale coherent PVC with double structure. In addition, a co-rotating large-scale secondary outer vortex rotates around the PVC. The characteristics of the double structure PVC are studied by analyzing its slope and strength, as well as the wavelength of the vortex. The mechanisms of interaction between the double PVC and flame are clarified over slices perpendicular to the vortex axis of the PVC. The analysis shows that across the vortex, a high velocity gradient occurs and no flame is identified in the vortex core region. A bit far of the vortex core, the flame is found to be strongly affected by the PVC. The flame front is highly curved, wrinkled, and rolled up around the vortex. In general, the double PVC is found to play an essential role in the stabilization of the premixed swirled flame.
Kim, Dohun; Son, Min; Koo, Jaye
doi: 10.1080/00102202.2016.1211865pmid: N/A
The pressure and temperature during liquid rocket engine ignition drastically increase because of energy generation from the severe combustion reaction of pure oxidizer and fuel. Studies on the ignition of oxygen/kerosene combustion are scarce. This research observes ignition transition of a gaseous oxygen/kerosene spray by directly visualizing the combustion flow field using a windowed combustor and high-speed shadowgraph imaging technique. The hydrodynamic characteristics of a propellant feed system are investigated before the ignition experiments by analyzing the time responses of propellant injection pressures and a high-speed movie of developing spray during injection. The experiments are performed with a 22.5 ms fuel pre-injection sequence. The high-speed shadowgraph imaging and dynamic pressure measurement results are analyzed. The effects of ignition timing on the ignition transition are focused on. The early ignition timing results in the smoothest ignition and longest ignition delay time from the propellant injection related to an ignitable transient spray condition. The combustion pressure rapidly increases with ignition timing delay. A peak pressure caused by propellant mixture accumulation is also observed. The ignition delay is less than 5 ms, and slightly decreases as the ignition timing is further delayed.
Agafonov, G. L.; Mikhailov, D. I.; Smirnov, V. N.; Tereza, A. M.; Vlasov, P. A.; Zhiltsova, I. V.
doi: 10.1080/00102202.2016.1211861pmid: N/A
Chemical ionization during the oxidation of methane and acetylene is experimentally and theoretically studied behind reflected shock waves over a wide temperature range and atmospheric pressure. The results of experimental measurements of the concentration of free electrons by microwave interferometry and electric probe method during the oxidation of acetylene and methane behind reflected shock waves are presented. A detailed kinetic model of the process of chemical ionization was developed. The results of experimental measurements and kinetic simulations are in good qualitative and quantitative agreement. The kinetic model of chemical ionization makes it possible to improve the kinetic description of the experimentally measured time histories of free electrons for the hydrocarbons studied.
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