Hot Jet Re-ignition of Hydrocarbons and Hydrogen in Air: Effect of Jet Chemical Activity

Abstract

A jet of hot reactive gas can reliably ignite premixed gases in combustion engines. The presence of chemically active species in the hot jet may influence the time delay and ignitability limits for ignition of a combustible mixture. Rapid ignition and combustion may also involve complex interactions of pressure waves with flames in the transient jet, especially in a wave-rotor constant-volume combustor for gas turbine performance enhancement. In the present work, detailed numerical simulations are carried out to understand the relative role of chemical kinetics and turbulent mixing in a transient hot jet on ignition in a constant-volume combustor. A transient hot jet is modeled in two ways: as a relatively inert hot jet and as a radical-rich chemically active hot jet for slightly rich ethylene-air mixture. Combustion is modeled in the main constantvolume chamber for methane, hydrogen and blended methane-hydrogen mixtures. A hybrid eddy-break-up combustion model is applied, with detailed or reduced reaction mechanisms and the two-equation k-ω model. For stoichiometric methane mixture in the main chamber, the predicted ignition of the blended fuel mixture was surprisingly not any faster than that of pure methane. The ignition delay time of the more chemically active jet is slightly shorter than a jet of similar composition with only stable species. These observations generally point to a complex interaction of physical and chemical process in hot-jet ignition in a confined volume with shock dynamics and jet mixing processes playing a role that may be as important as chemical kinetics.

Three-Dimensional Simulation of Turbulent Hot-Jet Ignition for Air-CH4-H2 Deflagration in a Confined Volume

“…Preliminary experiments suggest that slightly rich combustion in the pre-chamber provides the most rapid and consistent ignition, given ambient room conditions of pre-chamber initial mixture, for a wide range of CVC conditions [14,18]. Therefore, the equilibrium temperature, pressure, and composition of the pre-chamber at equivalence ratio of 1.1 is calculated and applied to all the cases for initializing the simulation [18,19]. The initial thermal and chemical properties of pre-chamber and CVC chamber are listed in Table 2.…”

“…Active radicals in the hot jet, such as CHx and OH, mix with the reactants and have been shown to play a significant role in the ignition process [18]. Thus, global reaction models for autoignition of reaction.…”

Ignition by Hot Transient Jets in Confined Mixtures of Gaseous Fuels and Air

“…The ignition of combustible mixture using hot inert jet or combusted products has been rarely studied numerically using global reaction mechanisms, and very few studies that use detailed or skeletal reaction mechanisms are known [18][19][20]. The present work seeks to use detailed numerical simulations to investigate the ignition by a hot jet and ensuing combustion of three hydrocarbon fuels (methane, propane, and ethylene).…”