A general structure of the specific optimal control has been previousl
y formulated and used to solve the fuel optimal problem of an aluminum
casting furnace. Proportional, integral, and derivative (P, I, D) clo
sed-loop control were applied to a 10-order nonlinear model of the fur
nace. This paper analyzes the resulting control actions and the dynami
c response to a step change in the target temperature of the liquid me
tal. it is shown that P and PD schemes ave stable but bring about a st
eady-state error; whereas PI and PID schemes cause no steady-state err
or but involve considerable oscillations in the transient response and
longer settling times. In view of the system's high thermal inertia a
nd the need to impose limits on fuel flow rate, it is found that a PD
scheme is the most appropriate due to the absence of over shoot and a
short settling time. The method is also applied to another optimizatio
n criteria, the minimization of temperature oscillations. This shows t
he applicability of the scheme to practical industrial problems.