Patent ID: 8733298

Claim:
Method for controlling operation of an internal combustion engine configured to combust fuel in a compression-ignition combustion mode, comprising: monitoring oxygen concentration in an exhaust gas feedstream of the internal combustion engine, mass flowrate of intake air, and a commanded fuel pulse of the fuel; determining a stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse; determining a first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel correlated to the stoichiometric air/fuel ratio of the fuel; and controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel; wherein determining the stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse comprises determining the stoichiometric air/fuel ratio in accordance with the following relationship: F x = 1 + AFR s 1 + W c / W f wherein F x is an exhaust gas mass burned fraction determined based on the oxygen concentration in the exhaust gas feedstream, AFR S is the stoichiometric air/fuel ratio of the engine fuel, W c is a mass of fresh air flow into an intake manifold of the engine determined based on the mass flowrate of intake air, and W f is an injected fuel mass determined based on the commanded fuel pulse.