The Flex-Fuel system requires the Fuel Pump to be corrosion resistant, ethanol compatible, and have a high flow rate. For example, let us consider the Bosch 044 series Fuel Pump. Its stainless steel pump casing (tensile strength 520 MPa) and fluororubber seal components (ethanol swelling resistance < 5%) can be utilized in E85 fuel (ethanol concentration 85%) for more than 150,000 kilometers, and the flow error rate is still ±2% (the error rate of ordinary pumps in E85 is more than ±8%). According to A study by SAE International, for the vehicle with shared Fuel pumps in E85 fuel, the impeller corrosion rate increases fourfold (with an average annual wear of 0.08 millimeters), the motor load current range expands from ±0.5A to ±1.8A, and the fault rate increases by 50%. In Brazil in 2021, due to the popularity of ethanol Fuel, material incompatibility was the reason for 23% of the Fuel Pump failures in Flex-Fuel models. The cost of maintenance was decreased by 35% after they were substituted with ethanol-resistant models.
The flow rate and pressure need to be calibrated based on the characteristics of ethanol fuel. The calorific value of ethanol is 30% lower compared to gasoline. The ECU has to increase the Fuel injection pulse width (e.g., from 3 ms to 4.5 ms) to maintain the air-fuel ratio. Therefore, the Fuel Pump flow rate has to be increased by 40%-50%. For example, the Ford F-150 Flex-Fuel vehicle utilizes the Walbro 450 L/h high-flow pump (65 psi pressure). In the E85 operating mode, the flow stability error is ±1.5 psi (±5 psi for the original factory pump), and the fuel injector life is extended from 80,000 kilometers to 120,000 kilometers. Delphi test shows that the detonation risk caused by pressure fluctuation in the original Fuel Pump in E85 increased from 2% to 15%, while following modification, the ECU correction dropped by 18% and fuel efficiency by 5%-8%.
Cost-effectiveness and technological innovation go hand in hand. The cost of ethanol-resistant Fuel pumps is approximately $200- $300 (as opposed to standard pumps at $120- $180), but the average annual maintenance cost is reduced by $200. The intelligent Fuel Pump jointly developed by Tesla and Bosch has an ethanol concentration sensor. It can adjust the PWM frequency (1 to 5 kHz) in real time, switch E10 and E85 seamlessly, reduce the flow error rate to ±0.8%, and increase the motor efficiency by 22%. The North American market data in the year 2023 show that 65% of Flex-Fuel models choose the intelligent Fuel Pump, which reduces the fuel-adaptive failure rate from 12% to 3% through CAN bus communication.
Material innovation guarantees long-term compatibility. The silicon carbide-coated impeller (15 microns thick coating) wears only 0.01 millimeters a year in E85 (0.06 millimeters a year for non-coated), and withstands a fuel temperature of 120°C (the limit for standard impellers is 90°C). General Motors’ 2022 HydroGreen Fuel Pump uses ceramic bearings (friction coefficient 0.02) and polyaryl ether ketone (PAEK) housing. It has a lifespan of up to 200,000 kilometers in E100 fuel, with a flow attenuation rate of less than 1%, at an extra cost of 25%. Frost & Sullivan predicts that the total market value of Flex-Fuel compatible Fuel pumps worldwide will be 4.8 billion US dollars in 2027, with the South American market holding 45% of this. The major driving factors include ethanol fuel’s penetration rate (target 60%) and carbon emission regulations’ requirements (ethanol emission reduction benefits up to 30%).