Electrical Conductivity Measurements via a Low-Voltage Conductivity Channel

The electrical conductivity in combustion gases with four different compositions (2% potassium with 0%, 10%, 15%, and 20% aluminum by mass added to a hydrocarbon fuel burned in gaseous oxygen) was determined experimentally using conductivity channels with two geometrical configurations, one with a constant bore and one with a tapered bore. Electrical conductivity for these conditions was calculated using the MACH2 numerical code, augmented with a transport property code. The fluid- mechanical conditions in the flow streams were also calculated using the axisymmetric and 1-D (NASA CEA) nozzle flow codes, both of which used the same transport property code to calculate the electrical conductivity. In the laboratory conductivity channel experiments, relatively low applied voltages were chosen to avoid unnecessary electrical heating of the test gas which might possibly have distorted the results. Results indicate that the measured conductivity increased linearly from approximately 10 mhos/m to 20 mhos/m as the aluminum was increased from 0% to 25% by mass. The results presented here differ markedly from those reported in shock tube experiments. The numerical simulation of the constant bore channel underpredicted the experiment within 15% and underpredicted the tapered-bore channel within 30%. The sources of uncertainties are addressed and provide some measure of confidence in the quality of the results. This is the first reported measurement of electrical conductivity values in the combustion products of a quasi-steady flow as a function of composition, together with the validation of these values with a 2-D computation.