Ignition and Flame Speed Kinetics of Two Natural Gas Blends With High Levels of Heavier Hydrocarbons

Abstract

High-pressure experiments and chemical kinetics modeling were performed to generate a database and a chemical kinetic model that can characterize the combustion chemistry of methane-based fuel blends containing significant levels of heavy hydrocarbons (up to 37.5% by volume). Ignition delay times were measured in two different shock tubes and in a rapid compression machine at pressures up to 34 atm and temperatures from 740 to 1660 K. Laminar flame speeds were also measured at pressures up to 4 atm using a high-pressure vessel with optical access. Two different fuel blends containing ethane, propane, n-butane, and n-pentane added to methane were studied at equivalence ratios varying from lean (0.3) to rich (2.0). This paper represents the most comprehensive set of experimental ignition and laminar flame speed data available in the open literature for CH4/C2H6/C3H8/C4H10/C5H12 fuel blends with significant levels of C2+ hydrocarbons. Using these data, a detailed chemical kinetics model, based on current and recent work by the authors, was compiled and refined. The predictions of the model are very good over the entire range of ignition delay times, considering the fact that the data set is so thorough. Nonetheless, some improvements to the model can still be made with respect to ignition times at the lowest temperatures and for the laminar flame speeds at pressures above 1 atm and rich conditions.

Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

“…To facilitate those estimates, we have built on the recent studies of smaller methyl esters noted above, which have established that H atom abstraction reactions depend mostly on the type (i.e., primary, secondary, tertiary, allylic, vinylic) of C-H bond is being broken. Rates of radical decomposition via β-scission, additions of molecular O 2 to alkyl radicals, rates of alkylperoxy radical isomerizations, and many other reactions of the methyl alkylperoxy radical isomerizations have been estimated based on past experience [39][40][41]51], with alkylperoxy systems.…”

“…For many of the elementary reaction in this core mechanism, rates have been studied experimentally or computed from first-principles electronic structure techniques. For the present study, we have adopted a recent small molecule mechanism of 10 Curran et al [51] which itself was built onto an even more basic H 2 /O 2 mechanism [52,53]. In addition, since the long straight-chain portions of methyl stearate and methyl palmitate are structurally identical to n-alkane molecules of similar length, we have included the n-alkane kinetic mechanisms developed recently for n-alkanes as large as n-hexadecane [41] and have extended those mechanisms to include n-C 17 H 36 to treat the 1-C 17 H 35 n-alkyl radical that can be produced from breaking the bond between the methyl ester group in methyl stearate and the long carbon chain containing 17 C atoms.…”

Simulation of ignition delay time of compressed natural gas combustion

“…This indicates that the sensitivity of reaction 2 increases with T. Reaction 2, O+OH<=>O2+H, to the right has a small activation energy (Ea), i.e., 0 cal/mol. Therefore, the reaction to the left, O2+H→O+OH, is considered to have fairly large Ea, as written in Bourque et al's mechanism [19], i.e., 16600 cal/mol. This shows that reaction 2 was one of the controllers in the elementary reactions, because it occurred at high temperature.…”

Fuel Flexible Turbine System (FFTS) Program

“…Also, no heat losses or diffusion effects are considered in the PSR model so the residence time that is calculated relies on the empirical data of the pure NG extinction limit. Figure 67 shows the residence time at extinction to be 0.053, 0.064, and 0.063 for Galway C5 (Bourque, Healy et al 2008), Galway nC5 (Healy, Kopp et al 2010), and GRI Mech 3.0 chemical kinetic mechanisms, respectively. This effective residence time at the extinction limit is then fixed in the PSR and EQ is varied until a reaction can no longer be sustained.…”