A Linearized Model of Engine Torque and Carbon Monoxide Emissions

Recently, an infrared diode laser spectrometer was developed which measures carbon monoxide (CO) exhaust emissions with a 25 ms response time. This rapid CO analyzer and a torque transducer were used to study the dynamic effects of air-fuel ratio perturbations about stoichiometry on CO emissions and engine torque, Linearised perturbation models expressed by transfer functions were obtained using frequency response techniques. The air-fuel ratio was perturbed around stoichiometry by varying either throttle position or fuel rate (via a modified Throttle Body Injection system) while holding the other parameter constant. Three speed-load points were studied in an engine dynamometer test cell to examine the effects of engine speed and load conditions on the structure and coefficients of the transfer functions.