Control system for determining biofuel content

An apparatus, comprising:

• an operation conditions module structured to interpret an intake O2 value, an exhaust O2 value, and a biofuel O2 correlation;
• an O2 fuel determination module structured to determine an O2 biofuel value in response to the intake O2 value, the exhaust O2 value, and the biofuel O2 correlation;
• a fuel composition module structured to determine a tank biofuel value in response to the O2 biofuel value;
• a biofuel reporting module structured to provide the tank biofuel value;
• and
• an engine operations module structured to adjust a fueling parameter in response to the tank biofuel value.

A method, comprising:

• interpreting a current operating condition, an exhaust NOx value, and a biofuel NOx correlation;
• determining a tank biofuel value in response to the current operating condition, the exhaust NOx value, and the biofuel NOx correlation;
• and
• reporting the tank biofuel value.

A system, comprising:

• a direct injected internal combustion engine having an exhaust outlet and running excess oxygen;
• a NOx sensor in flow communication with an exhaust stream within the exhaust outlet, the NOx sensor providing at least one of an exhaust O2 value and an exhaust NOx value;
• and
• means for determining a biofuel value in response to the at least one of an exhaust O2 value and an exhaust NOx value.