Speaker
Mrs
Anne Rodriguez
(CNRS-LRGP Nancy France)
Description
Due to the current issue concerning the growing primary energy demand, not to mention a general interest in sustainable development, bio-fuels became very fashionable in recent years. They are subject to a lot of research on combustion with the characterization of the reactivity and pollutant emissions. The molecule of dimethyl ether (DME) has led to a strong interest in the field of combustion. Corresponding to the simplest linear ether (CH3-O-CH3), it has a high cetane value (55-60) and a low toxicity. Promising studies have highlighted key-strengths of this molecule as an additive agent or even an alternative diesel fuel. Among these advantages, we find a particularly significant decrease in the formation of soot and NOx particles.
Due to its simplicity, DME is a good choice for understanding the mechanisms of ether oxidation. It exhibits typical “two-stages” ignition characteristics common to many hydrocarbons: low temperature, negative temperature coefficient, and hot ignition phenomena. Several experimental and theoretical studies have investigated on DME combustion, using various equipments (jet-stirred reactor, shock-tube, counterflow diffusion flame, variable-pressure flow reactor...) and at different operational conditions. Even if they bring essential information, they are unable to predict a single valid model for all circumstances. The objective of this study is to investigate DME oxidation with a different approach in order to complete existing experimental data, and subsequently better understand its reaction mechanism.
This was done with several experiments carried out in a jet-stirred reactor operating at 800 Torr, 500-1100 K, and at different equivalence ratios: 0.25, 1 and 2. The products obtained have been analyzed using two complementary methods: gas chromatography (GC) and cavity ring-down spectroscopy (CRDS). GC is efficient in separating compounds and allows us to analyse a wide range of products like CO, CO2, hydrocarbons, CH3CHO and CH3OCHO ; while CRDS is an absorption spectroscopic technique and allows us to analyze species such as CH2O, H2O and H2O2 (undetectable by GC).
Profiles of DME conversion and products were compared with expected theoretical profiles (cf. Zhao et al., J. of Chem. Kin. 2008,401-18). While they are quite similar at high temperatures, a significant difference appears at low temperature (from 500 to 750K). Whatever equivalence ratio studied, the model overestimates the conversion of the reactant over this range of temperature. Pre-established mechanisms are then not yet optimal and should be improved to better predict the oxidation of DME.
Primary authors
Mrs
Anne Rodriguez
(CNRS-LRGP Nancy France)
Dr
Christa Fittschen
(CNRS-PPCA)
Dr
Olivier Herbinet
(CNRS-LRGP)
Mrs
Ophélie Frottier
(CNRS-LRGP)
