A system (400) and method of determining fuel demands of a locomotive engine (10) based upon engine speed and power produced by the engine at a given time, so to optimize the engine's power output for a load while reducing engine emissions. The engine control architecture comprises three interrelated control loops (100–300). A primary feedback control loop (100) employs integral type control with gain scheduling to regulate engine speed to commanded slew rated based upon the locomotive's operator commands. A second control loop (200) provides an active, feed forward or predictive control consisting of a plurality of correction functions each utilizing a Taylor series having coefficients for each term in the series, the coefficients being modified to adapt the system to the engine with which it is used. A control third loop (300) optimizes reference speed slew rates and engine load rates by providing feedback of nominal engine fuel requirements or fuel demand, corrections to fuel demand based upon outputs from the second control loop, speed error values, and ambient conditions.