The use of alcohols as alternative fuel is becoming more and more prevalent. One of the biggest challenges to using alcohols as fuel is the difference in the Stoichiometric Air to Fuel Ratio (SAFR) of gasoline to that of alcohols. The differing SAFRs means that the fuel pump and fuel injectors must supply a different volume of fuel depending on the concentration of alcohol in the fuel. This challenge is further exacerbated by the fact the different types of alcohols have different SAFRs.
A conventional flex fuel sensor is able to determine the concentration of ethanol in a given fuel, or alternately, the concentration of methanol in a given fuel. The shortcoming of this technology is that it cannot measure both. Each sensor must be calibrated for either ethanol or methanol, and will be inaccurate if the other is present in the fuel. This limitation in measurement flexibility would cause problems in a market that offers both alternative fuels.
An alternate conventional solution employs a wide range oxygen sensor, also known as a Lambda sensor. This method employs an oxygen sensor in the exhaust line to measure the amount of oxygen remaining after combustion. The fuel to air ratio is then adjusted accordingly. This is a feedback method and can only make adjustments after combustion has already taken place. A refueling event can cause a large shift in the alcohol content, which can take several minutes for the Lambda sensor to detect. This delay results in excess emissions and loss of performance of the vehicle, while the system “learns” the properties of the new fuel.
A conventional near infrared sensor can eliminate the concentration of gasoline, methanol, and ethanol blends with good accuracy. However, the cost of the near infrared sensor is high, and the sensor can suffer from environmental and durability limitations.
Thus, there is a need to provide a sensor system for measuring the permittivity, conductivity and temperature of a given fuel and for outputting the SAFR so as to be fed forward to an engine control module.