Cyclopentadiene combustion in a plug flow reactor near 1150 K

Abstract

Cyclopentadienyl (CPDyl) was generated for study by oxidizing and pyrolizing 1,3-cyclopentadiene (CPD) in Princeton’s adiabatic, atmospheric pressure flow reactor. This study used nitrogen carrier gas, initial CPD concentrations from 1000 to 3000ppm by volume (ppmv), equivalence ratios from fuel lean (ϕ=0.6) to pyrolytic conditions (ϕ=100) and initial temperatures from 1100 to 1200K. The reaction progress was followed from 5 to 150ms using a water cooled sample probe and GC–FID analysis of C1–C14 species. The oxidation results show that CPD and CPDyl react via 19 pathways to yield 22 hydrocarbon intermediates. Analysis of the oxidative CPDyl ring opening pathways reveals the importance of the 2,4-cyclopentadienoxy (c-C5H5O) β-scission reaction: c-C5H5O↔CHCH–CHCH–CHO. The fastest theoretical mechanism has a calculated unimolecular high-pressure rate constant of 2.00×1013e−7215/Ts−1 which is seven orders of magnitude larger at 1150K than the previous literature estimate. Cyclopentadienone (CPDone) has been assumed to be an important intermediate in C5 ring oxidation even though it has not been unambiguously identified in the combustion environment. A detection limit of 20ppmv for CPDone in the present apparatus failed to note any CPDone. A set of mechanistic pathways for the C5 ring oxidation includes steps to avoid unrealistic CPDone production is presented. The complex mechanism illustrates the need for detailed models to understand the combustion of aromatics and soot precursors. The article stresses the importance of CPDyl in the formation of aromatic rings during combustion, which subsequently leads to polycyclic aromatic hydrocarbons (PAH) and soot precursors.