A method can be used for determining fuel consumption of an internal combustion engine of a vehicle, in real time. The method includes determining a fuel injection quantity of the internal combustion engine based on an oxygen concentration signal from an oxygen sensor and a MAF signal from a mass airflow (MAF) sensor. The MAF sensor is coupled to the intake line and is configured to measure and monitor the mass flow rate of intake air flowing through the intake line. The method further includes determining, via an engine control module (ECM), an instantaneous fuel flow of the internal combustion engine based on the fuel injection quantity. The method further includes communicating, via the ECM, the instantaneous fuel flow to a body control module (BCM) and determining, via the BCM, an average fuel economy of the internal combustion engine based on the fuel flow.

A combustion speed, for example, is estimated or evaluated, with a required accuracy, more simply than the conventional art, while reducing man-hours to produce a heat generation rate waveform of an internal combustion engine. An increase rate of a heat generation rate relative to a change in a crank angle in a heat generation rate increasing period (e.g., a first-half combustion period a) in which the heat generation rate increases after ignition of an air-fuel mixture is defined as a heat generation rate gradient b/a that is one of characteristic values of the heat generation rate waveform. The heat generation rate gradient is estimated based on a fuel density (e.g., fuel density .sub.fuel@dQpeak at heat generation rate maximum time) at a predetermined time set in advance in the heat generation rate increasing period so as to produce the heat generation rate waveform using the estimated heat generation rate gradient.

A first-half combustion period, for example, is estimated/evaluated, with a required accuracy, more simply than the conventional art, while reducing man-hours to produce a heat generation rate waveform of an internal combustion engine. Within a combustion period of an air-fuel mixture, a period from an ignition time FA to a heat generation rate maximum time dQpeakA where the heat generation rate is maximum is defined as the first-half combustion period a that is one of characteristic values of the heat generation rate waveform. The first-half combustion period a is estimated based on an in-cylinder volume at the heat generation rate maximum time, and furthermore by being corrected using an exponential function of the engine rotation speed with a value depending on a tumble ratio as exponent. Thus, the heat generation rate waveform is produced using the estimated first-half combustion period a.

A combustion speed, for example, is estimated or evaluated, with a required accuracy, more simply than the conventional art, while reducing man-hours to produce a heat generation rate waveform of an internal combustion engine. An increase rate of a heat generation rate relative to a change in a crank angle in a heat generation rate increasing period (e.g., a first-half combustion period a) in which the heat generation rate increases after ignition of an air-fuel mixture is defined as a heat generation rate gradient b/a that is one of characteristic values of the heat generation rate waveform. The heat generation rate gradient is estimated based on a fuel density (e.g., fuel density .sub.fuel@dQpeak at heat generation rate maximum time) at a predetermined time set in advance in the heat generation rate increasing period so as to produce the heat generation rate waveform using the estimated heat generation rate gradient.

In order to provide a flow rate measurement device that can measure a flow rate of a sample fluid passing a tube body with high accuracy even though temperature irregularity of the sample fluid generates along a radial direction of the tube body, the flow rate measurement device comprise a temperature measurement device that measures a mean temperature of a sample fluid discharged from an internal combustion engine or temperature distribution of the sample fluid along a radial direction of the tube body, and a flow rate of the sample fluid is measured based on the mean temperature or the temperature distribution measured by the temperature measurement device.