Method and apparatus for performing modal mass analysis of exhaust gas

Abstract

A method and apparatus for measuring the quantity of an ingredient gas in the exhaust gas from a motor vehicle with a known engine displacement during a time period in which the vehicle is driven over varying driving modes (modal mass analysis). The resultant measurement is achieved without use of a constant volume sampling device by first measuring and storing data C.sub.E (t) representative of the concentration of the ingredient gas in the exhaust gas at successive time intervals during the period. The vehicle speed during each successive time interval is measured and stored, followed by calculating theoretical exhaust flow rate values Q.sub.Ei (t), representative of the flow rate of the exhaust gas for each of the succession of time intervals, based on the known engine displacement and the measured engine speed. Then approximate actual exhaust flow rate values Q.sub.Ea (t) are calculated using a polynomial curve fit method on the calculated theoretical flow rate values Q.sub.Ei (t). Lastly, the quantity M(t) of the ingredient gas in the exhaust gas for each of the succession of time intervals is determined on the basis of the operational equation