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Laminar flame speed measurements were carried for mixture of air with eight C3-4 hydrocarbons (propene, propane, 1,3-butadiene, 1-butene, 2-butene, iso-butene, n-butane, and iso-butane) at the room temperature and ambient pressure. Along with C1-2 hydrocarbon data reported in a recent study, the entire dataset was used to demonstrate how laminar flame speed data can be utilized to explore and minimize the uncertainties in a reaction model for foundation fuels. The USC Mech II kinetic model was chosen as a case study. The method of uncertainty minimization using polynomial chaos expansions (MUM-PCE) (D.A. Sheen and H. Wang, Combust. Flame 2011, 158, 2358-2374) was employed to constrain the model uncertainty for laminar flame speed predictions. Results demonstrate that a reaction model constrained only by the laminar flame speed values of methane/air flames notably reduces the uncertainty in the predictions of the laminar flame speeds of C3 and C4 alkanes, because the key chemical pathways of all of these flames are similar to each other. The uncertainty in model predictions for flames of unsaturated C3-4 hydrocarbons remain significant without considering fuel specific laminar flames speeds in the constraining target data set, because the secondary rate controlling reaction steps are different from those in the saturated alkanes. It is shown that the constraints provided by the laminar flame speeds of the foundation fuels could reduce notably the uncertainties in the predictions of laminar flame speeds of C4 alcohol/air mixtures. Furthermore, it is demonstrated that an accurate prediction of the laminar flame speed of a particular C4 alcohol/air mixture is better achieved through measurements for key molecular intermediates formed during the pyrolysis and oxidation of the parent fuel.

In this experimental study, the pressure dependence of the extinction strain rate of flames of jet fuel and other hydrocarbons was measured and quantified. Laminar nonpremixed opposed-jet flames of fuel/nitrogen mixtures versus oxygen-enriched air were progressively strained to extinction by lowering pressure over the pressure range 0.1 to 0.68 atm. The fuels investigated were methane; ethylene; Jet-A; n-decane; 1, 2, 4-trimethyl benzene; and blends of n-decane and 1, 2, 4-trimethyl benzene. All liquid fuels were vaporized and diluted to a mass fraction of 21.5% in nitrogen gas; the gaseous fuels were not diluted. The oxidizer was a 50/50% molar mixture of oxygen and nitrogen. The global strain rate at extinction was seen to monotonieaHy increase with pressure in the subatmospheric pressure range explored. Overall reaction orders calculated from density-weighted extinction strain rates were between 1.3 and 2.0. Jet-A flames were extinguished at conditions similar to those for the decane/trimethyl benzene blends, indicating that these blends can serve as a surrogate for Jet-A. DOI: 10.2514/1.42742

This study investigates the differences between oxycombustion and conventional air combustion through methane flame extinction measurements and calculations. We report global extinction strain rates for methane with O2/N2, O2/CO2, and O2/CO2/H2O flames for a range of calculated stoichiometric adiabatic flame temperatures. Tests were performed in a subatmospheric opposed-jet burner, with pre-vaporized water. For a given oxidant diluent, global extinction strain rates increase strongly with increasing flame temperature and with pressure. At a given temperature, the effect of oxidant composition depends on whether dissociation is included in computing the stoichiometric adiabatic flame temperature. When dissociation is included, O2/CO2and O2/CO2/H2O flames are roughly 30% harder to extinguish than O2/N2flames. When dissociation is not included, the oxidant composition has a minimal effect. Calculations with the CHEMKIN suite of programs yield the same ranking of extinction strain rate for the different additives, when stoichiometric adiabatic flame temperature is matched with dissociation included. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation characteristics of C2 hydrocarbons were revisited in flames established in the counterflow configuration. Laminar flame speeds of ethane/air, ethylene/air, and acetylene/oxygen/nitrogen mixtures as well as extinction strain rates of non-premixed ethane/air flames were measured using digital particle image velocimetry. The experiments were modeled using three different kinetic models. While the experimental and computed laminar flame speeds agreed closely for all C2 hydrocarbons under fuel-lean conditions, notable discrepancies were identified under fuel-rich conditions. Using the computed flame structures, insight was provided into the controlling mechanisms that could be responsible for the observed discrepancies. More specifically, the uncertainties associated with the kinetics of the thermal decomposition of the ethyl radical were found to be a potential source of the observed discrepancies for ethane flames. It was shown also by using alternative rate constants for the ethyl radical decomposition, the rate of flame propagation and the extinction propensity are affected notably. Furthermore, the values of the branching ratio of acetylene consumption reactions involving atomic oxygen were found to have a significant effect on the propagation of rich acetylene flames. [Copyright &y& Elsevier]