SENSITIVITY ANALYSIS OF AN EXHAUST-EMISSIONS-BASED AIR FUEL RATIO MODEL FOR GASOLINE-ENGINES/

This paper reviews some existing models for calculating air:fuel ratio based on analysis of exhaust-gas emissions, as an alternative to the conventional direct measurement of the Row rates of air and fuel. A co mprehensive model for accurate calculation is proposed, and a study is made of the model's sensitivity due to instrument errors in measuring emission concentrations. Results show that only four emission paramet ers-hydrocarbon, carbon monoxide, carbon dioxide and oxygen-are requir ed for accurate calculation of air:fuel ratio. The sensitivity paramet ers of these emissions are low relative to the sensitivity parameters due to errors in measuring rates of fuel- and air-flow. The total abso lute sensitivity of the former is about a tenth of the latter at stoic hiometric air:fuel ratio. This means that to obtain an accurate air:fu el ratio for an IC engine, instruments used for measuring fuel- and ai r-flow rate should have at least ten times the accuracy of the emissio n analysers, especially for gasoline engines where equivalence ratio i s determined at unity. A point is mooted: should a method based on exh aust emissions be regarded as the 'standard method' for measuring the air:fuel ratio in gasoline engines?