Optimal Use of E85 in a Turbocharged Direct Injection Engine

Ford Motor Company is introducing EcoBoost gasoline turbocharged direct injection (GTDI) engine technology in the 2010 Lincoln MKS. A logical enhancement of EcoBoost technology is the use of E85 for knock mitigation. The subject of this paper is the optimal use of E85 by using two fuel systems in the same EcoBoost engine: port fuel injection (PFI) of gasoline and direct injection (DI) of E85. Gasoline PFI is used for starting and light- medium load operation, while E85 DI is used only as required during high load operation to avoid knock. Direct injection of E85 (a commercially available blend of similar to 85% ethanol and similar to 15% gasoline) is extremely effective in suppressing knock, due to ethanol's high inherent octane and its high heat of vaporization, which results in substantial cooling of the charge. As a result, the compression ratio (CR) can be increased and higher boost levels can be used. The increased full load BMEP allows downsizing of the engine at equivalent or enhanced vehicle performance. By enabling higher CR and engine downsizing, the use of E85 DI + gasoline PFI makes the engine more efficient in its use of gasoline, thereby leveraging the effect of the available ethanol in reducing the consumption of gasoline. This leveraging has a profound influence on ethanol's net energy balance and CO2 reduction potential. The vehicle owner will realize high fuel economy because gasoline, with its high heating value per volume, is primarily used for most driving modes in a downsized, high CR engine. In this paper, the concept of E85 DI + gasoline PFI is assessed using a Ford Motor Company 3.5L turbocharged direct injection EcoBoost engine. A PFI system was added to the engine and CR was increased to 12:1. The amount of E85 required to avoid knock was quantified as a function of BMEP at various engine speeds on an engine dynamometer. A full load torque curve subject to the peak pressure and turbine inlet temperature constraints of the engine was also acquired. A vehicle simulation program was then used to quantify the amount of E85 required for various drive cycles, and to determine vehicle fuel consumption.