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 C3H8 and C4H10 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 CH3OCH3, while the sensitivity factors of the H-abstraction and the decomposition of C3H8 (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 C3H8 and C4H10 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.