Percent Ethanol Estimation on Sensorless Multi-Fuel Systems; Advantages and Limitations

Ethanol is a widely used automotive fuel alternative. To improve it's market acceptance multiple fuel capability is important. Engine management systems were recently introduced that reduce the add-on cost of multiple fuel capability by deleting the ethanol sensor and work with exhaust oxygen sensor feedback to estimate the Ethanol content in the fuel. These systems show a %Ethanol estimation accuracy of better than 4% over the entire %Ethanol range with nominal components. If stacked-up production tolerances of all components are considered this estimation accuracy is significantly worse introducing some undesirable side effects on fuel and spark delivery. Special care has to be taken in calibration, or specific engine management algorithms should be introduced, to minimize the impact of these side effects. In order to optimize performance on all percentages of Ethanol an adaptive knock control system as part of the engine management system should be used. For the Brazilian situation, that has E20 and E100 commercially available, system performance can be improved by limiting the learn range at the low side to E20.