Laser-based speciation of isoprene thermal decomposition behind reflected shock waves

Abstract

Isoprene holds significant relevance in the realm of atmospheric and combustion chemistry due to its widespread occurrence in both natural and anthropogenic sources. Despite the pivotal role of isoprene in global emissions and combustion scenarios, a detailed understanding of its speciation during thermal decomposition is lacking. Leveraging recent advancements, our focus is on time-resolved speciation behind reflected shock waves, providing precise quantification of the mole fraction time histories of major products. Using a low-pressure shock tube, we investigate isoprene pyrolysis over temperatures of 1280–1780 K and pressures ranging 2.8 to 3.2 bar. Employing multi-wavelength analysis technique, five laser beams are co-aligned through the shock tube to measure the evolution of five major hydrocarbons, namely isoprene, methane, ethylene, acetylene, and 1,3-butadiene, offering a comprehensive overview of isoprene pyrolysis. Comparison of the measured data with the predictions of literature kinetic models shows the inadequacy of existing models. Our proposed model, featuring an updated isoprene pyrolysis subset, enhances predictability and highlights the intricate chemistry of isoprene pyrolysis. Rate of production and sensitivity analyses are used to illustrate key pathways responsible for the formation of observed species. This work will help advance our understanding of isoprene's role in combustion chemistry and pollutant formation, facilitating the optimization of future energy systems.