Percent Ethanol (PM) Estimation with Sealed Fuel Tank Information (Antoine Equation & Raout’s Law)
Publication Date: 2014-Oct-06
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Percent Ethanol (PM) Estimation with Sealed Fuel Tank Information (Antoine Equation & Raout's Law)
Certain in-vehicle OBD diagnostic monitors (ex: EVAP EONV) requires foreknowledge of percent ethanol (PM) for robustness purposes. The ethanol content is typically inferred from the UEGO sensors during engine combustion. While PM estimation works well with traditional (ICE engine only) setup, they don't lend themselves appropriately for HEV or PHEV where the ICE engine may not operate regularly. This is because the current source of estimation is UEGO sensing during ICE operation. Without frequent updates from such mechanism and the fact PHEV and HEV may take longer time to consume the same amount of fuel compared to an ICE engine only setup, over time E80 may become E70 or lower. This presents risks for fuel economy, emission control, drivability and various powertrain control problems. In this disclosure, we demonstrate a calculation that will update such information recursively with usage of well-known Antoine's Equation and Raout's Law. The method is independent of ICE engine operation.
The method is based on Antoine's Equation which approximates vapor pressure and temperature as a linear function is a transformed scale as the following: or
From Raout's Law, constant A and B are weighted combination of known mixtures. For example, E15's A and B constant are approximated if E10 and E100 are known. As a numeric example, E91's A constant would be approximat...