Flex fuel and Flexstart system

Flex fuel and Flexstart systems
  • Function
    Versatile – economical – sustainable

    Flex fuel vehicles from Bosch have an injection system which can be operated with gasoline, with any mixture ratio of gasoline and ethanol or with pure ethanol. Regardless of the supply situation concerned, end customers are flexible when it comes to the choice of fuel and are able to respond to any price developments immediately.

    Ethanol as a fuel

    Derived from plants, ethanol is an alcohol that can be used as a fuel. Ethanol is added to the gasoline, the ethanol proportion can be between 5 and 85 %. E100 is a fuel with 93 % ethanol and 7 % water, with no gasoline admixture.

    The combustion basis of flex fuel and Flexstart systems forms the tried and proven port fuel injection technology. The networked system components precisely detect the ethanol proportion at all times. The control unit adjusts the air/fuel ratio accordingly, in order to transmit the requested torque cleanly and economically. Thanks to continuous further development, Bosch offers systems for direct injection too.

    Flex fuel und Flexstart systems

    Because ethanol is difficult to ignite at temperatures below 13 °C, vehicles with the flex fuel system have a small auxiliary fuel tank onboard. On the basis of sensor data, the control unit automatically switches to gasoline drive to guarantee a reliable and convenient start. After a short heat-up phase, the system reverts to ethanol drive.

    Moreover, Bosch has expanded its range by the innovative Flexstart system. It heats up - where necessary – the fuel via electronically-controlled heating elements in the fuel rail, which, thereby permitting a smooth start and drive even at low temperatures. Consequently, the second fuel system and the auxiliary tank for pure gasoline are not required in these vehicles, and start comfort on cold days can be optimized.

    Flex fuel with direct injection

    Through consistent further development, Bosch also permits flex fuel systems to be used in combination with direct injection. Flex fuel systems with direct injection (such as flex fuel and Flexstart based on intake manifold fuel injection) use a mixture of ethanol and gasoline as a fuel. Engines with direct injection generate the air/fuel mixture in the combustion chamber itself. The fuel is injected directly into the combustion chamber via high-pressure injection valves.

    The flex fuel system with direct injection offers additional advantages over flex fuel systems with port fuel injection. Air and fuel are precisely metered, prepared and distributed for each combustion cycle. The result: reduced consumption and lower emissions with higher engine output.

  • Customer benefits
    Tapping market potentials

    Alongside conventional combustion technology, alternative fuels are becoming increasingly important. Bosch offers customized engine management systems and injection components for the use of alternative fuels. As a pioneer in this field, Bosch began large-scale production of the flex fuel technology for the ethanol drive of gasoline engines in 1986 and has been consistently further-developing this technology ever since.

    In South America, ethanol produced from plants is a frequently used addition to convention gasoline. The world's leading market for ethanol vehicles is Brazil, where approx. 90 percent on new registered vehicles are ethanol-powered. But USA and Sweden are also seeing increasing use of flex fuel vehicles, which can be driven with 85 percent ethanol-admixture to the gasoline (E85).

    Flexibility with the choice of fuel

    For many customers, flexibility with the choice of fuel is the key argument for buying flex fuel technology. With this technology, you can always resort to the most economical fuel. If ethanol is not available as a fuel, flex fuel system vehicles can also be re-fueled just with gasoline. Flex fuel systems from Bosch guarantee mobility, irrespective of the ethanol supply.

    The high anti-knock properties of ethanol (110 octane) also allow vehicle manufacturers achieve a higher compression ratio. And thereby a higher engine output. Ethanol achieves an additional performance increase for turbocharged engines: E85 and particularly E100 with a 7 percent water content removes heat from the hot charge air upon evaporation (internal cooling). The air-gas mixture cooled as a result has a higher substance content for the same volume. This improves the engine's volumetric efficiency, thereby additionally increasing the power output – the best conditions for downsizing.

    Resource-friendly mobility

    Alternative fuels contribute towards economical and sustainable mobility. Especially with flex fuel systems, ethanol has become established as a fuel that can be added to conventional gasoline at a ratio of 5 to 85 %. Also, methanol can be used as a fuel.

    Until now, Ethanol has mainly been distilled from sugar cane or starch-containing grains. New technologies are based on the biomass use of cellulose-containing raw materials such as China grass. In this way ethanol, leads to a marked reduction in the CO₂ balance.

    Flex fuel systems also create a benefit from an economic perspective, since they reduce dependence on crude oil: instead of oil fields, only arable land is required. Using ethanol as a fuel means we are less dependent on prices and the availability of fossil fuels. This also creates potentials for developing new economic sectors in the fuel and vehicle industry.

  • Flexstart innovative system
    Maximum start convenience at cold temperatures

    The Flexstart system has the same functionality as flex fuel, along with additional benefits. It permits a smooth cold start with pure ethanol (E100) even at low outside temperatures. Unlike conventional flex fuel systems, the Flexstart system from Bosch does not require an auxiliary gasoline tank, since the ethanol is heated. This function is performed by electrically-controlled heating elements in the fuel rail. Without the driver noticing, it heats up the ethanol and thereby ensures an optimal start.

    The heated fuel rail heats up the ethanol to the required temperature, and so improves the ethanol evaporation process. Unlike conventional ethanol systems, the Flexstart technology is able to avoid emissions at engine start and reduce the required injection quantity.

    The Flexstart system maximizes the driver's sense of comfort. He can re-fuel with any ethanol and gasoline ratio, yet needs to keep his eye on just one fuel gage. As early as the heat-up phase, the optimized combustion process ensures outstanding engine operation and fewer impurities in the engine oil.

    At a glance

    • good start and driving behavior at lower outside temperatures
    • lower emissions than conventional cold-start systems (up to 2 % CO₂ and up to 15 % HC)
    • more convenient re-fueling
  • Automotive competence
    Comprehensive portfolio and extensive expertise

    Bosch develops and manufactures flex fuel technology for a broad vehicle segment, from motor cycles to passenger cars to light-duty commercial vehicles. For flex fuel vehicles, Bosch offers a broad product range for the vehicle functions of fuel supply, fuel injection, air control, ignition, engine control, turbocharging, thermal management, exhaust aftertreatment, transmission technology and start/stop. The range of components is rounded out by the innovative Flexstart system solution and flex fuel technology with gasoline direct injection.

    Systems competence and comprehensive know-how

    Bosch has a comprehensive understanding of drive systems. This includes knowledge of numerous technical parameters, correlations and dependencies of a flex fuel system. Bosch's system expertise ensures the optimal design of the individual components and hence maximum system efficiency. Networking the system with intelligent software achieves optimum functionality, even with differing fuel mixture ratios.

    Driving innovation and technology

    As an innovation driver in the automobile industry, Bosch is making sure that innovative technology is being developed to the large-scale standard for flex fuel systems too. With Flexstart, Bosch has launched the first series-produced system for cold start with ethanol fuel. The Brazilian Ministry for Science and Technology has recognized Bosch for its Flex Fuel technology with the "Technological Innovation Finep Award". Bosch has also received, in Brazil, the "Automotive Business" award and the coveted "Auto data" award in the "Technology Innovation" category.

    Ensuring quality and reliability

    Bosch technology for flex fuel vehicles meets the highest technical performance requirements and offers a high degree of functional safety and reliability. The high quality of this technology is down to years' of experience in the development of flex fuel systems. Bosch has been developing and manufacturing technology for flex fuel systems since 1986. Bosch's high quality standard contributes significantly to the reliability of the flex fuel systems, even with inferior fuel compositions.

    Global presence

    With flex fuel drive system experts, Bosch enjoys proximity to automobile manufacturers worldwide, knows the specific local requirements for the technology and understands the peculiarities through local development and manufacture.

    Development centers for flex fuel technology exist in Europe (Schwieberdingen, Germany), Asia (Shanghai, China), North America (Farmington Hills, Michigan) and South America (Campinas, Brazil). Bosch also helps local vehicle manufacturers develop new markets.

    Long-term partnership

    Bosch supports vehicle manufacturers' flex fuel activities throughout the vehicle's entire life cycle, from the design of new vehicle concepts, of the development and application to series production to vehicle service. At the same time, Bosch contributes extensive knowledge of cooperative partnerships with the vehicle manufacturers, offers knowledge transfer and thereby helps market the jointly developed technology to the end customer.


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