A Comparison Between the Combustion of Isooctane, Methanol, and Methane in Pulse Flame Combustors with Closed Loop A/F Control

CO/H₂ (ratios i.e. water gas shift equilibria) in exhaust gases produced from the combustion of pure isooctane, methanol, and methane in a pulse flame combustor were measured. Measured CO/H₂ ratios were directionally consistent with C/H ratios of the respective fuels. The average CO/H₂ ratios in combusted isooctane, methanol, and methane were found to be 3.8, 1.25, and 2.0, respectively. The effect of these differences on feedback A/F control with a HEGO (heated exhaust gas oxygen) sensor were also examined. Feedback control of isooctane combustion produced operation very near to stoichiometry. On the other hand, the combustion of methanol under feedback control resulted in steady state lean operation while feedback control of methane combustion produced rich operation. For all three fuels, operation shifted in the lean direction as combustion efficiency was degraded. In addition, evidence is provided which indicates that the differences in control characteristics between isooctane, methanol, and methane are the result of H₂ enriching and incomplete equilibration of CH₄ at the HEGO sensor electrode.