Two-stage ignition of DME/air mixture at low-temperature (<500 K) under atmospheric pressure

Abstract

Low-temperature ignition characteristics of dimethyl ether (DME)/air mixture were studied in an external heated, straight-shaped, plug-flow reactor under atmospheric pressure. Auto-ignition of the mixture was attained under a specific narrow range of temperature and equivalence ratio with relatively longer exposure time. Three kinds of ignition behaviors were identified accordingly as the equivalence ratio increased, such as (1) periodic hot flames, followed by (2) periodic two-stage ignitions (weak flame(s) and subsequent hot flame), lastly (3) chaotic weak flames. Time-sequential gas analyses were conducted for the case showing a typical periodic two-stage ignition in order to investigate the mechanism of the observed low-temperature auto-ignition under 500 K. The results revealed that the formation of CH 4 and C 2 H 2 was promoted prior to the hot flame ignition, suggesting that the chain-branching reaction pathway might exist.The transition from weak flame to hot flame was clearly observed as the mixture equivalence ratio decreased, implying the oxygen could be responsible to trigger this transition. It is suspected that the chain-branching precursor CH 2 OCH 2 OOH radicals should be relatively stable in the examined temperature range here, thus can gradually accumulate through a longer exposure time, and eventually give rise to the chainbranching explosion.* Corresponding author. Address: Hokkaido University, Kita13 Nishi8, Kita-ku, Sapporo 060-8628, Japan. Tel. & fax: +81-11-706-6386. E-mail address: yuji-mg@eng.hokudai.ac.jp Two-stage Ignition of DME/air Mixture at Low-temperature (<500K) under Atmospheric Pressure 2 Keywords: dimethyl ether, low-temperature oxidation, low-temperature auto-ignition, flames with repetitive extinction and ignition (FREI), two-stage ignition, cool flame.Two-stage Ignition of DME/air Mixture at Low-temperature (<500K) under Atmospheric Pressure 3 Highlights ► Auto-ignition of DME/air mixture was captured in a specific narrow range in temperature and equivalence ratio. ► Weak flame is transited to hot flame as equivalence ratio decreases.► CH 4 and C 2 H 2 formed due to the chain-branching reaction pathways.

Analysis of the Kinetics and Yields of OH Radical Production from the CH3OCH2 + O2 Reaction in the Temperature Range 195–650 K: An Experimental and Computational study

“…While DME use clearly reduces sooting in compression-ignition engines, controversies exist with respect to its capability to reduce NOx, hydrocarbon, and CO emissions as well. 6,7 Detailed chemical kinetic models of DME autoignition, pyrolysis, and oxidation under varying temperature / pressure / equivalence ratio / residence time conditions have been developed and tested against data from several experimental systems, including jet stirred reactors, [8][9][10] rapid compression machine 11 , variable-pressure flow reactors, [12][13][14][15][16] shock-tubes [17][18][19] and direct sampling from flames. 20,21 Despite considerable experimental and modelling effort there is still a significant lack of understanding 22 of rates, products, and mechanisms of several important reactions, particularly reactions of the methoxymethyl radical (CH3OCH2).…”

High-Pressure Study of Methyl Formate Oxidation and Its Interaction with NO

“…Methods to reduce both emissions include high-pressure injection, turbocharging, and the use of fuel additives; the latest is thought to be one attractive and effective solution . Dimethyl ether (DME) and dimethoxymethane (DMM) are two examples of promising additives for diesel fuel and/or substitutes. − Methyl formate (MF, CH 3 OCHO) has been found to be a byproduct of the oxidation of several proposed fuel alternatives, such as these two, DME − and DMM. , MF is the simplest ester, and esters are the primary constituents of biodiesel. , MF has also been considered as a model molecule used to understand biodiesel and other such real fuel molecule combustion. , …”

Evaluation of Combustion Mechanisms Using Global Uncertainty and Sensitivity Analyses: A Case Study for Low‐Temperature Dimethyl Ether Oxidation

“…For Φ = 0.75 and T = 649 K, the isomerization reaction dominates with smaller contributions from the CH 2 OCH 2 O 2 H + O 2 = O 2 CH 2 OCH 2 O 2 H, O 2 CH 2 OCH 2 O 2 H = HO 2 CH 2 OCHO+OH, and HO 2 CH 2 OCHO = OCH 2 OCHO + OH channels. The reactions of hydroperoxymethyl formate are therefore an important pathway for the formation of OH in the current form of all the mechanisms although Gao and Nakamura question whether there are other possible secondary OH formation routes. At the higher temperatures, the competition between chain‐propagation QOOH = OH + 2CH 2 O and chain‐branching QOOH + O 2 increases in importance and the relative importance of the reactions of hydroperoxymethyl formate reduces.…”