Sliding Mode Control of High Exhaust Gas Recirculation Diesel Engines, 03-R8010Printer Friendly Version
Inclusive Dates: 12/11/08 04/13/09
Background - Progressively stricter regulation of exhaust emission from engines has prompted a particular interest in management of pollutant production at source, i.e., in-cylinder of a (diesel) engine. Management of pollutant production in conjunction with moderate exhaust treatment (diesel particulate filter (DPF), lean NOx trap (LNT), selective catalytic reduction (SCR) etc.) is considered by many as a cost-effective means to meet the regulation. One of the paradigms to manage pollutant production in-cylinder is that of the so-called airflow-dominant fueling. This "fuel follows air" approach simultaneously affords combustion stability and managed pollutant production at source. However, an inherent weakness of such a strategy is that the torque response of the engine suffers if the air-supply is insufficient. Sluggish torque performance could result particularly in the case of a turbocharged engine where the air-supply and the fueling are inherently interdependent exhaust energy available to the turbocharger depends on fueling, but the fueling itself depends on the available air-supply.
Approach - To address the sluggish torque response we defined appropriate targets for the manifold states (pressure, oxygen concentration, and temperature) and developed a controller factorization with a sliding mode controller and a multi-port actuator controller as factors. The sliding mode controller operated on error in the manifold states and generated flow change commands to eliminate the error. The multi-port actuator controller operated on the commanded flow changes and generated position change commands to the flow-control devices. SwRI used a physically based model of the engine system along with singular value decomposition (to understand interactions) to derive the two controller factors. An explicit model of the turbocharger was not required.
Accomplishments - An appropriate combination of "airflow-dominant fueling" and "active management of air" lends good control over pollutant production and torque performance. Good torque response with reasonable NOx spike and low opacity was achieved with the method. The method was verified via constant-speed up and down torque transients. Pedal up-transients from an idle condition to maximum torque were achieved in approximately two seconds. NOx spikes were controlled to double the steady-state levels. No noticeable opacity spikes were observed. This compares favorably to the engine under its stock control, which has NOx spikes of four times the steady-state levels and opacity spikes of 35 percent or greater.