Warm Start Robustness Improvement Using the Heated Cold Start System in Flex Fuel Engines

摘要

This paper presents a new ethanol content identification concept, with focus on flex fuel vehicles start ability robustness. The solution refers to the usage of cold start system based on heated fuel rail (normally used for low temperatures) in a preventive way like an ethanol sensor, ensuring a successful start attempt in specific conditions, even at high ambient temperatures. At most of flex fuel projects, the ethanol content calculation (or the percentage of ethanol in fuel) is done through the oxygen sensor (also called lambda sensor). Therefore the engine start strategy considers the fuel mixture determined in the previous vehicle operation. In situations when the adaptation cycle is not completed during the operation cycle previous to the start attempt, and also in combination with an extreme fuel exchange situation after tanking (previous to the last vehicle operation cycle), it may happens that the first start attempt is not successful. In this case the engine management strategy acts reactively to ensure a proper engine start and drivability until the correct ethanol content is calculated. The new concept heats the fuel in these specific conditions, using this additional fuel line ethanol content information to adjust the mixture parameters, ensuring the start ability. Thus, the engine management is not anymore reactive and can preventively act before the engine start, improving the flex fuel system robustness without the need of additional components.