Ignition of Non-Premixed Flames of Ethylene/-Dodecane Blends

Abstract

Ignition temperatures of non-premixed flames of ethylene/-dodecane blends were measured and modeled in the counterflow configuration at atmospheric pressure and an unburned fuel-carrying stream temperature of 453 K. Ethylene is an important product of the thermal decomposition of large molecular weight -alkanes such as -dodecane that produces ethylene via scission. Thermal decomposition is expected in scramjet applications in which the fuel is also used as the vehicle and engine coolant. Thus, the ignition process of the mixtures of the parent molecule and products of decomposition could be among the controlling factors of operation in hypersonic propulsion. In the present study, laser Doppler velocimetry was used to measure local strain rates and thermocouples were used to measure ignition temperatures. Simulations of the experiments were performed using four kinetic models, and comparisons were made against the experimental data. Notable discrepancies were found between the data and the predictions, as well among the predicted ignition temperatures. Through sensitivity and reaction path analyses, insight was gained into the physicochemical couplings during the ignition of binary fuel flames, and the sources of the discrepancies were identified to be of both kinetic and molecular transport natures. It was determined that there is an interesting kinetic coupling between these two fuels at the ignition state, given that, upon blending, ethylene acts as both a fuel and an intermediate of the decomposition of -dodecane.