A high-pressure jet-stirred reactor study of di-iso-pentyl ether oxidation and detailed kinetic modelling

In this study, the oxidation of di-iso-pentyl ether (DIPEE) is investigated for the first time. Dilute mixtures (DIPEE/O 2 /N 2 ) were oxidized in a jet-stirred reactor at 10 atm, between 450 and 1210 K and at a residence time of 0.7 s. Four mixtures were tested with equivalence ratios of 0.5, 1, 2, and 4. In the low/intermediate temperature region, about 40 species were identified and quantified through FTIR and GC-FID-MS analyses. Given the quantified intermediates, it was observed that alkyl radical intermediates such as iso-pentyl and iso-butyl radicals appear to play an important role as intermediates in DIPEE oxidation. The most abundant oxygenated intermediate species at low temperature include formaldehyde, iso-pentanal, acetaldehyde, and acetone with mole fractions greater than 100 ppm. Besides, species such as iso-butanal, isopentanoic acid, isoamyl formate, and isoamyl alcohol were also identified and quantified. DIPEE has very high reactivity (here, it starts to oxidize at 470 K) and exhibits two distinct zones of negative temperature coefficient before the high-temperature zone, which can also be referred to be as a double-cool flame. This behavior is due to the interactions caused by the low-temperature chemistry of the alkyl radicals within the cool flame regime. A detailed kinetic sub-mechanism for DIPEE oxidation was developed including detailed low-temperature reactions of species like iso-pentanal and iso-butanal, based on our previous studies. While the kinetic mechanism predicts the experimental profiles reasonably well, there is room for improvement especially for the rate constants of the low-temperature reactions of the oxygenated species for which very few theoretically obtained or directly measured values exist. Novelty and significance statement This is the first time di-iso-pentyl ether is studied for its combustion kinetics (detailed speciation and kinetic mechanism). Our ether oxidation mechanism is updated with this new sub-mechanism and used to explain the “unconventional” double cool-flame behavior exhibited by this fuel. This is a rather recent and hence under-studied area of low-temperature oxidation. This study on di-iso-pentyl ether reveals similarities and differences between the trends observed with dialkyl ethers previously studied in the same experimental set-up under same thermodynamic conditions. With >30 products identified, it helps constraining the kinetic mechanism while pointing out sources of inaccuracies commonly encountered but not necessarily addressed. Some of these ethers have the potential to be a biofuel, but they also contribute to the understanding the fundamentals of low-temperature chemistry dealing with the double cool-flames.