Low-temperature gas-phase oxidation of diethyl ether: Fuel reactivity and fuel-specific products

Abstract

Diethyl ether (DEE) has been recently suggested as a potential biofuel for compression-ignition engines that are known to be significantly controlled by low-temperature (LT) chemistry. However, the LT oxidation of DEE has not fully been understood in term of the formation of LT fuel-specific products. We have thus studied the oxidation of DEE by examining detailed profiles of its oxidation products under LT conditions (400–1100 K). To this end, we have used a dedicated experimental setup including a nearly-atmospheric jet-stirred reactor (JSR) coupled to online gas chromatography (GC). The experiments were complemented by measurements made with a JSR coupled to tunable synchrotron vacuum ultraviolet (SVUV) photoionization (PI) molecular-beam mass spectrometry (MBMS) for a cross-validation of the identification of important LT species.Experimental results indicate that DEE is very reactive; it starts to react around 425 K. DEE exhibits an unusual oxidation behavior with two negative temperature coefficient (NTC) zones in the JSR study. Because of this two-NTC observation, additional experiments were performed with a plug flow reactor (PFR) combined with electron ionization (EI)-MBMS, confirming this behavior in the two types of reactor. Moreover, about 20 oxidation species in C1C4 range were detected with several intermediates containing 2-3 O-atoms. Acetic acid is found to peak at 525 K with a very large amount, suggesting that it is a key species in the early stage of DEE's LT oxidation. Possible DEE-consumption paths leading to acetic acid formation could play an important role in the oxidation mechanism of DEE. A new model is proposed based on the present experimental observations to include new primary LT reaction paths. The model reproduces the experimental phenomena quite well and enhances the understanding of the two-NTC-zone occurrence and of intermediates containing 2-3 O-atoms during the LT oxidation of DEE.