Study on the explosion characteristics of propanal/air mixtures at elevated pressures

Propanal is a crucial intermediate speciates generated from the combustion of biofuels. To understand its for-mation pathways and optimize the clean combustion of biofuels, accurate determination of its laminar burning speed at engine-like conditions is essential. Additionally, propanal can be used to produce propionic acid by reacting with air under elevated pressures, which is a process that inherently poses a significant explosion risk. To address the above issues, the effects of initial pressures (0.1-1.0 MPa) and fuel concentrations (2.56-9.52%) on the explosion pressure and laminar burning speed of propanal/air mixtures were investigated. Results show that the relationship between the explosion pressure and fuel concentration was satisfactorily fitted by a cubic polynomial function. By comparing the laminar burning speed obtained using the constant volume method (CVM) and kinetic studies, the reliability of the kinetic model at elevated pressure was verified. According to the sensitivity analysis of elementary reactions affecting the flame temperature, the major elementary reactions affecting the combustion of propanal were analyzed. From fuel-lean to stoichiometric concentration, the com-bustion of propanal is dominated by the reaction kinetics of H2 and CO, while alkyl relevant mechanism controls the kinetics at fuel-rich conditions. At the fuel-lean conditions, recombination reactions were triggered during the collision of the excess oxygen molecules with reactive radicals. However, on the fuel-rich side, recombination reactions involving O2 progressively weakened. In addition to being affected by the equivalent ratio, elementary reactions are also profoundly influenced by the initial pressure. However, the effect of initial pressure on the elementary reactions is influenced by the fuel concentration. As the concentration of propanal is below the stoichiometric concentration, the sensitivity of elementary reactions increases gradually with the increasing initial pressures, while it no longer varies monotonously as the equivalence ratio reaches 1.5.