Douglas Ray Hamburg

A Closed-Loop A/F Control Model for Internal Combustion Engines

A mathematical model is developed which describes the operation of an A/F control system containing an engine, an exhaust gas oxygen sensor, and a feedback controller. The dependence of model parameters on engine operating conditions is discussed, and the model is used to compare integral and proportional/integral control algorithms. Actual data obtained on an engine-dynamometer are presented to test the validity of the model.

AN ENGINE-DYNAMOMETER STUDY OF THE A/F COMPATIBILITY BETWEEN A THREE-WAY CATALYST AND AN EXHAUST GAS OXYGEN SENSOR

An engine-dynamometer study was performed to quantify the air-fuel ratio (A/F) offset between the window of a three-way catalyst (TWC) and the closed-loop control point of an exhaust gas oxygen (EGO) sensor. In this study, the effects of rpm, torque, EGR, and A/F modulation were explored along with the age of the TWC and EGO sensor. In general, it was determined that the closed-loop EGO sensor control point shifts lean as a function of increasing feedgas NOx concentration, thus causing the engine A/F to move away from the high NOx conversion efficiency regime of the TWC.

The Effect of EGR System Response Time on NOx Feedgas Emissions during Engine Transients

Quantitative measurements were made of NOx feedgas emissions during transient engine operation as the response time of an EGR system was progressively degraded. For a simple acceleration-cruise-deceleration engine speed/torque versus time trajectory, it was found that the NOx emissions were higher during acceleration and lower during deceleration than corresponding values predicted from steady-state mapping data. The magnitude of the differences, as well as the total mass of NOx integrated over the speed/torque trajectory, all increased as the EGR response time was increased. Using a simple dynamic EGR model, NOx feedgas emissions were predicted for engine operation with a production EGR system over a 128 second portion of the FTP CVS cycle. The NOx feedgas predictions were shown to be in excellent agreement with actual emission measurements.

ENGINE DYNAMOMETER STUDY OF THE TRANSIENT RESPONSE OF ZRO2 AND TIO2 EXHAUST GAS OXYGEN SENSORS

The transient response of ZrO2 and TiO2 EGO sensors has been investigated under actual engine operating conditions. The results of this study show that the response of an EGO sensor is dependent upon the characteristics of the engine and feedback control system with which it is used. Specifically, sensor response time is a function of the magnitude and frequency of the A/F changes and the initial and final values of A/F to which the sensor is exposed. ZrO2 and TiO2 sensors show similar transient behavior and have practically equivalent response times.

A Comparison Between Predicted and Measured Feedgas Emissions for Dynamic Engine Operation

Vehicle chassis dynamometer tests were performed to compare predicted and measured total feedgas emissions and fuel economy for dynamic operation of an engine. In general, the tests showed that predictions based on steady-state mapping data agreed well with measured values except for NOx emissions. Subsequent engine-dynamometer tests indicated that the discrepancy between predicted and measured NOx emissions was due to competing effects of combustion chamber wall temperature and dynamic EGR time response. A technique was developed which utilized the results of a simple transient test to improve the accuracy of predicting NOx emissions when EGR time response was not a factor. The effect of degraded EGR time response on both instantaneous and total NOx emissions was also explored.