Simultaneous measurements of temperature, CO, and CO2 time-history in reacting n-heptane/O2/argon mixtures blended with diethyl ether behind reflected shock waves

Abstract

The temperature, CO, and CO2 time-histories for the fuel-rich (equivalence ratio ϕ = 1.2 and 2.0) oxidation of n-heptane/diethyl ether/O2/argon mixtures were measured simultaneously in a shock tube using laser absorption spectroscopy. Two transition lines (v" = 0, P8, 4.73 μm and v" = 1, R21, 4.56 μm) in the CO fundamental band were selected to simultaneously measure the temperature and CO time-histories. One transition line in the CO2 fundamental band (v3“= 0, R88, 4.18 μm) was used for the CO2 time-history measurements, with its absorption cross-section measured at 1240 – 2600 K and 0.7 – 3.8 bar. A kinetic model was then developed that combined the NUI Galway 1.1 mechanism and the DEE sub-mechanism (Sakai et al. 2017). All the measured data were compared with predictions based on the proposed mechanism and the Zeng et al. (2017) mechanism.Both mechanisms accurately predicted the near-equilibrium/plateau temperatures for ϕ = 2.0 and CO for ϕ = 1.2. However, for ϕ = 1.2, both mechanisms slightly overpredict the near-equilibrium temperature and CO2. For ϕ = 2.0, the presented mechanism better predicts the CO plateau concentrations while the Zeng et al. (2017) mechanisms are better in predicting CO2 plateau concentrations. The predictions were less accurate for the temperature rise and CO/CO2-evolution processes. The predictions were also less accurate for specific equivalence ratios and blending ratios of n-heptane and diethyl ether. Rate-of-production analyses showed that HCO + M = H + CO + M is the primary pathway for producing CO and CO + OH = CO2 + H is the primary pathway for producing CO2 for the conditions in this manuscript. Sensitivity analyses show that the most sensitive reaction is H + O2 = OH + O, with some reactions related to AXC3H5 and CH3CHO also influencing the CO and CO2 time-histories. Modifying the rate constants of the specific reactions reduces the differences between the predicted and measured results, but discrepancies still exist and the mechanisms need to be further improved.