Combustion and Flame, Vol.215, 66-77, 2020
Ignition delay time and laminar flame speed measurements of mixtures containing diisopropyl-methylphosphonate (DIMP)
Diisopropyl-methylphosphonate (DIMP) is a common surrogate of Sarin for which a detailed kinetics mechanism was developed in 2002 (Glaude et al.-). In the present paper, ignition delay times and laminar flame speeds of DIMP-based mixtures were studied around atmospheric pressure for the first time. Methane and hydrogen were used as baseline fuels, and mixtures of these fuels were doped with DIMP. The DIMP was added at 10% mol. of the fuel concentration for the shock-tube experiments (three equivalence ratios (0.5, 1.0, and 2.0) were investigated with methane). A stoichiometric DIMP/O-2 mixture was also studied. For the laminar flame speed experiments, an equivalence ratio sweep was performed, and DIMP was added at 0.1% vol. of the total mixture, although DIMP was added to up to 0.5% vol. for the maximum flame speed condition with H-2. Results showed that adding DIMP promotes the ignition of methane but also largely inhibits its laminar flame speed. A decrease in the flame speed with DIMP addition was observed with H-2 as well, and the maximum flame speed was found to decrease linearly with the amount of DIMP added. The new results with DIMP were compared to data obtained recently for other Sarin surrogates. The influence of the structure of these surrogates on combustion properties was discussed. The kinetics model for DIMP does not capture the peculiar OH* profiles observed in the shock tube for the DIMP/O-2 mixture, and the ignition delay times for the H-2-DIMP mixture were very poorly predicted. On the other hand, ignition delay times for the CH4-DIMP mixture were predicted with goodto-fair agreement for most cases. A chemical analysis showed that a sub-mechanism for iso-propanol needs to be added to the mechanism. An updated detailed kinetics model, with a state-of-the-art hydrocarbon chemistry (including iso-propanol chemistry) and updates in the phosphorous chemistry and thermodynamic database was tested. This updated mechanism provides predictions that are less accurate than the original model in most cases, indicating a strong need to revisit the reactions describing the thermal decomposition of DIMP. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.