Ionization in flames: current-voltage relationships for the flame ionization detector

An analysis is made of the ionization current drawn from a flame ionization detector having cylindrical symmetry. An idealized representation of the flame is used which enables a relation to be defined between the applied voltage and the current drawn from the flame, and the expression contains factors dependent on geometry and concentration. Results of experiments confirm the basic form of this expression for both positive and negative currents drawn from a premixed hydrogen + nitrogen + oxygen flame. The expression also holds for positive currents drawn from the hydrogen + nitrogen diffusion flame, but cannot yet satisfactorily account for negative currents at high rates of flow of hydrogen.