The improvement of fuel efficiency is one of important challenges in research and development of a vehicle, and for further improvement, it is important to measure instantaneous fuel consumption related to behavior of an engine.
To instantaneously measure fuel consumption, direct measurement by a fuel flowmeter is commonly used. However, in the case of a completed vehicle, the measurement using a fuel flowmeter is difficult. Also, it is not easy to, without disturbing any fuel system condition, place a fuel flowmeter in a fuel flow path.
For this reason, for example, a method (carbon balance method) that obtains emission mass from respective exhaust gas component concentrations in exhaust gas diluted by a CVS, and from the emission mass, calculates fuel consumption is used (e.g., JPA-2-234021). The carbon balance method is one that calculates fuel consumption from amounts of carbon contained in respective components of CO2, CO, and HC in exhaust gas.
However, in the case of the method that introduces the diluted exhaust gas diluted by the CVS into an exhaust gas analyzer through a sampling flow path, and measures the component concentrations of CO2, CO, and HC in the exhaust gas, it takes time for the diluted exhaust gas to be introduced into the exhaust gas analyzer through the sampling flow path, and therefore a response delay occurs. For example, measurement of fuel consumption of a vehicle that frequently performs a fuel cut and switching to electrical driving makes a response delay due to gas congestion caused by the sampling flow path particularly noticeable, and therefore may be unsuitable for the instantaneous fuel consumption measurement.