Oxidation study of small hydrocarbons at elevated pressure part II: A two-fuel compound mixture of acetylene and 1,3-butadiene

Abstract

The high-pressure oxidation experiments of a two-fuel component mixture of 0.2%1,3-butadiene (1,3-C4H6), 0.2% acetylene (C2H2), nitrogen (N2) and oxygen (O2) (see Table 3, No.1 & 2) were carried out in a jet-stirred reactor (JSR) at 12 atm within 575–1025 K under fuel-lean (φ = 0.5) and fuel-rich (φ = 3.0) conditions. 15 species profiles of products and intermediates were identified and quantified by gas chromatography (GC) and gas chromatography-mass spectrometer (GC–MS). This work is enlarging the experimental data base obtained from the study of C2H2/1,3-C4H6 mixtures reported earlier. The updated comprehensive chemical reaction kinetic model based on the experimental data of the current work and the AramcoMech 3.0 model is containing 635 species and 3291 reactions. The comparison between the new experimental data base and the data predicted by the updated model was done for major products and intermediates, such as oxygenated species and aromatics. In general, a good agreement was found. It was shown that the fuel-rich oxidation of C2H2/1,3-C4H6 mixtures (see Table 3, No.2) contributes largely to benzene (C6H6) formation compared to neat oxidation of C2H2 (see Table 3, No.4) as well as of 1,3-C4H6 (see Table 3, No.6). At temperatures below 900 K, C6H6 is mainly formed through the C2 + C5 channel: C2H2 + C5H5 → C6H5CH2 → C6H6. The C2 + C4 pathway: C4H5-I/N + C2H2 → FULVENE → C6H6 tends to be the dominant route for C6H6 formation at temperatures above 900 K. A rate-of-production (ROP) analysis indicates that both C2H2 and 1,3-C4H6 are consumed mainly by addition reactions with mainly OH radicals involved. The consumption of C2H2 decreases with increasing values of the fuel-equivalence (φ), while the consumption of 1,3-C4H6 is much less effected by the specific φ values. Compared with the results obtained at fuel-lean condition (φ=0.5), the C3H5-A and C5H5 radicals consume more C2H2 with increasing temperatures at fuel-rich condition (φ=3.0). The oxidation process of 1,3-C4H6 is occurring mainly by H-abstraction with OH radicals, H-addition, and subsequent reactions. According to sensitivity analysis, the reaction H2O2 (+M) ⇌ OH + OH (+M) can promote the consumption of C2H2 and of 1,3-C4H6; however, the promoting effect gradually decreases with increasing of φ values. On the other hand, the consumption of C2H2 can also be promoted by the reactions C3H5-A + C2H2 ⇌ CVCCVCCJ and 1,3-C4H6 + OH ⇌ C3H5-A + CH2O, in addition, the promotion effect can gradually enhance with increasing φ values. For 1,3-C4H6 consumption, the promoting effect of the reaction 1,3-C4H6 + CH3 ⇌ C4H5-I + CH4 also strengthens. The results of the present work contribute to a better understanding of benzene formation at high-pressures in particular and provide valuable information for the study of the formation pathways of PAHs and soot as well.