Experimental and Kinetic Study on Ignition Delay Times of Liquified Petroleum Gas/Dimethyl Ether Blends in a Shock Tube

Abstract

In this study, ignition delay times of liquified petroleum gas (LPG)/dimethyl ether (DME) (LPG consists of C 3 H 8 and C 4 H 10 in this work) were measured in a shock tube at different DME blending ratios (0%, 10%, 30%, and 50%), pressures (5, 10, and 15 atm), temperatures (1100–1500 K), and equivalence ratios (0.5, 1.0, and 1.5). The chemical kinetic mechanism of LPG/DME was established based on Lawrence Livermore National Laboratory’s C1–C4 chemical kinetic mechanism ( Combust. Flame 1998, 114, 192–213) and Zhao’s DME chemical kinetic mechanism ( Int. J. Chem. Kinet. 2008, 40, 1–18), and its predictions agree well with experimental data. A sensitivity analysis and a reaction pathway analysis were conducted using CHEMKIN-PRO to study the impact of DME addition on the ignition and combustion process. The experimental results show that the ignition delay times of LPG/DME change linearly with increasing DME blending ratios. The sensitivity analysis shows that the number of major promoting reactions for mixtures increases, including H-abstraction and decomposition of CH 3 OCH 3, while the sensitivity factors of the H-abstraction and the decomposition of C 3 H 8 (reactions R115, R120, and R125) decrease with increasing DME blending ratios. The reaction pathway analysis indicates that the H-abstraction reactions play a dominant role, and the contribution rate of OH to H-abstraction increases, while that of H-radical decreases slightly in the oxidation of C 3 H 8 and C 4 H 10 with the increasing proportion of DME in the LPG/DME mixtures. Further analysis shows that although the growth rate of H before ignition is LPG100 > LPG50 > DME, reaction R22 in the oxidation process of mixtures makes OH accumulate rapidly in a short time, resulting in a much higher peak concentration of OH than that of H; therefore, the ignition delay times of mixtures are shorter than those of neat LPG.