Patent ID: 8381513

Claim:
A compression-ignition internal combustion engine system comprising: a compression-ignition engine, an exhaust passage and an exhaust gas treatment arrangement, wherein the exhaust gas treatment arrangement comprises a single catalyzing device being a three-way catalytic converter and a diesel particulate filter located downstream of the three-way catalytic converter in a direction of exhaust gas flow; further comprising an electronic control unit including instructions for: operating the engine so as to control the flow rate of gases into one or more combustion chambers of the engine and/or to control the injection of fuel into said one or more combustion chambers to provide stoichiometric combustion over a predetermined range of engine load; in a first mode, at low engine loads, operating the engine at high EGR rates under normal diesel combustion to reduce NOx emissions, in a second mode, at medium to high engine loads, operating the engine under stoichiometric conditions where NOx emissions can be reduced by way of the three-way catalytic converter and, in a third mode, under very high engine loads and/or engine speeds, operating the engine under normal diesel combustion conditions and low EGR rates to obtain maximum torque; operating the engine in an air-lead mode whereby the intake air flow rate is controlled to achieve a demanded torque and an amount of fuel injected is controlled to obtain a target air/fuel ratio based upon the intake air flow rate; operating the engine in an air-lead mode during quasi steady state engine conditions and under a fuel-lead mode during conditions of rapid changes in torque demand.