Mass flow rate determination

A method of operating an internal combustion engine, comprising:

• receiving a first input and a second input both indicative of operation of an inlet air compressor or the internal combustion engine;
• inferring respective inlet air compressor mass flow rates of a first characteristic field and a second characteristic field, the first and second characteristic fields being of a compressor map, where the first and second characteristic fields are two sections of a common compressor speed curve divided by a maximum pressure ratio of the curve;
• selecting one of the inferred inlet air compressor mass flow rates based on a comparison of an inlet air compressor mass flow rate inferred at a region crossing in the compressor map to a sensed inlet air compressor mass flow rate;
• and
• adjusting one or more operating parameters of the internal combustion engine based on the selected inferred inlet air compressor mass flow rate.

A mass air flow sensor for an inlet air compressor of a turbocharger, comprising:

• a first input for receiving one of a compressor speed and an engine speed;
• a second input for receiving one of a compressor output pressure and an engine torque;
• a first characteristic field for inferring a first compressor mass flow rate based on the first and second inputs according to a first region of a compressor map;
• a second characteristic field for inferring a second compressor mass flow rate based on the first and second inputs according to a second region of the compressor map;
• a selection unit for selecting one of the first and second inferred compressor mass flow rates based on a comparison of a compressor mass flow rate inferred at a region crossing in the compressor map to a sensed compressor mass flow rate, the first region of the compressor map structured to infer compressor mass flow rates for relatively low engine speeds and loads, and wherein the second region of the compressor map is structured to infer compressor mass flow rates for relatively high engine speeds and loads.