Temperature Effects on Gaseous Fuel Cracking Studies Using a Dielectric Barrier Discharge

Fuel cracking using a plasma is one of the methods to enhance combustion by forming lighter hydrocarbons and hydrogen from heavier ones. Lighter hydrocarbons and hydrogen burn more cleanly and under much leaner burn conditions, thereby increasing combustion stability and producing less pollution (particularly oxides of nitrogen - NOx). The cracked fuel fragments are also expected to efficiently burn more, and thus, more energy can possibly be extracted from the fuel. Fuel cracking is accomplished at Los Alamos National Laboratory by using an AC annular dielectric barrier discharge (also called a silent electrical discharge). This forms a nonthermal plasma between the barrier (a ceramic tube) and the central electrode, which is typically charged to 5-10 kV. The nonthermal plasma is relatively cold, since electrons carry most of the energy and the ions and neutrals remain at approximately ambient temperature. Our experiments show that increased temperature inside the reactor elevates the stable concentration of CH₄ (methane), C₂H₂ (acetylene), C₂H₄ (ethylene), and C₃H₈ (propane) from a C₂H₆ (ethane) parent gas. The AC waveform was used to heat the dielectric barrier, which in turn heated the nonthermal plasma in the reactor. Results of these experiments were compared to a KINEMA model of ethane plasma chemistry. The model predicts the same global trends as the experimental data. This modeling shows that certain radical-forming reactions, and direct pathways for H₂, CH₄, and C₃H₈, have enhanced reaction rates at higher temperatures compared to the ambient case.