Opportunity for Plastics in Extended-range Electric Vehicle Fuel Tank

Introduction

An Extended-range Electric Vehicle (E-REV) is a Plug-in Hybrid EV (PHEV) that uses an electric drive train and an Internal Combustion Engine (ICE) for the propulsion of vehicles. When a battery is discharged, the ICE acts as a range extender by generating additional electric power that supplies power to the electric drive and recharges the battery. The battery present in an E-REV has a much larger capacity of 10–20 kWh as compared to a conventional battery present in EVs, whereas the engine is smaller as it is only required to meet the limited power demand. Thus, an E-REV overcomes the range limitation of a BEV. An E-REV operates in a full electric mode for moderate distances, whereas it utilizes the ICE to charge the battery in case of long distances. (Source: International Journal of Engineering and Advanced Technology (2014))

The ICE in E-REVs consumes less fuel as compared to conventional Internal Combustion Engine Vehicles (ICEVs). There are mainly two reasons for it: the smaller size of engine present in an E-REV and the engine that operates at a constant, highly-efficient rotation speed of E-REV.

Storage tanks in automobiles

A fuel tank in an ICE-based vehicle that is dependent on its capacity and fuel efficiency to cover maximum distances. Larger tanks are heavier; though they increase the maximum distance covered by a vehicle, they take up more space. Traditionally, automotive fuel storage tanks are made up of either metal or plastic. (Source: General Motors Demonstration Project (1998))

Storage tanks that are made up of metal include steel or aluminum tanks welded from stamped sheets. Plastic fuel tanks are made from High-density Polyethylene (HDPE) by blow molding. HDPE-based blow-molded plastic tank can take complex shapes, which directly helps to save space. However, HDPE lacks in terms of safety and long-term ability to function.

Plastic fuel tank in extended-range electric vehicles

Plastic fuel tank3 in E-REV is replacing tanks used in conventional internal combustion engine vehicles. The weight of this plastic tank is less than the traditional metal tank used in ICE-based vehicles. TI Automotive manufactured a double molded plastic tank for Karma Automotive, a luxury electric car manufacturer. The plastic tank produced by TI Automotive for Karma is a lightweight tank that can handle high vapor pressure created in E-REVs, which allows optimization of the vehicle’s full electric operating range driving mode. (Source: Plastics Today (2019))

TI Automotive has a patented technology to produce plastic fuel tank and has been awarded PACE innovation award for its Tank Advance Process Technology (TAPT) manufacturing process in 2014. TI Automotive uses TAPT manufacturing process to manufacture advanced plastic tanks to meet various vapor pressure requirements of E-REVs. This process helps to develop different types of plastic fuel tanks from a single design blow tooling set. The traditional method of sourcing different tanks is based on engine type or region. TAPT enables the global standardization of complete vehicle platforms.

History of plastic fuel tanks

Components of fuel vapor control system

Fuel vapor is generated inside a fuel tank due to temperature and displacement. Evaporative hydrocarbon emissions are ejected during the combustion process. However, this does not happen with hybrid electric vehicles when running on electric mode. At high temperatures, the pressure accumulated inside the tank will be substantially higher than in a conventional fuel system. As this saturated vapor pressure of volatile gasoline is high at elevated temperatures, the plastic fuel tanks are susceptible to deformation. Fuel vapor control system in a vehicle controls pressure grades to be discharged or reduces the pressure inside the fuel tank.

The fuel vapor control system of a hybrid electric vehicle includes a temperature sensor, pressure grades, tumble sensor cut valve, and fuel level sensor. The temperature sensor is mounted on the top wall of a fuel tank. A pressure control valve has one end communicating with the shut-off valve, and the other end communicates with the canister. The electronic control unit that radiolabels fuel tank vapor pressure is calculated with the volume of the oil level to record changes in vapor temperature, pressure, and volume parameters. When the vapor pressure increases and reaches the maximum, the electronic control unit alarms a signal and prompts the engine of electric vehicles to start functioning.

Plastic fuel tanks in Europe accounted for more than 80% in 2015; this percentage is similar in case of North America. Automobile giants such as BMW, Daimler, Fiat Chrysler, Ford Europe, GM Europe, Honda, Peugeot – Citroen, Porsche, Renault-Nissan, Suzuki, Toyota, and Volkswagen prefer the use of plastic fuel tanks.

Advantages of plastic fuel tank

Lightweight4: In case of metal tank, the considerate weight of the high-density steel tank is ~8 times higher than HDPE. The wall of the HDPE-based tank is 3–4 times thicker than the steel tanks. Steel tanks are also very expensive due to the high cost of stamping. For example, a steel tank of a standard passenger car is ~21.92 kg, whereas the plastic tank weighs around 14 kg. A plastic fuel tank also helps in significant savings in use phase energy as compared to steel. This contributes to low energy requirement of a vehicle and potentially saves the fuel cost. Noise reduction is one of the most important parameters of electric vehicles. Plastic tanks dampen noise and vibrations in the cabin of electric vehicles. (Source: China Automotive Review – 2019)

Corrosion resistance5: Fuel tanks are generally exposed to corrosion due to the action of fuel and other external elements, such as mud, salt, gravels, etc. on the road. A plastic fuel tank is highly resistant to corrosion. Water vapor is formed inside a half-empty metal tank, which, in turn, results in rusting; however, the non-corrosive plastic tank is immune to rusting. (Source: Total Plastics Solutions – 2017)

Cost6: The cost of a plastic fuel tank is comparatively lesser than that of a traditional steel tank. The use of plastics not only reduces the cost of materials but also reduces the cost of maintenance. However, multilayer plastic tanks have barriers to meet standards that are being imposed on evaporative emissions. This adds to the final cost of the plastic fuel tank that in certain instances, reaches the same price as that of steel. (Source: International Journal for Innovative Research in Science & Technology – 2015)

Various shapes: Lightweight plastics can be molded into multiple shapes of tanks allowing them to fit into the provided space, and thus, reducing the final weight of vehicles. The leftover negative space can be filled by designing the plastic fuel tank at the end of car designing phase.

Service: The plastic industry offers a full-service in fuel tank operation by participating in designing tanks, building it, and sending the final product to an OEM. This is opposite to the steel industry that only provides steel; however, work related to offering a shape to the tank is undertaken by the OEM.

Disadvantages of plastic fuel tanks

Safety: There is a significant risk when a plastic fuel tank is subjected to fire. The plastic fuel tank is more likely to melt, and the fuel inside can flow out, which would eventually cause an explosion.

New plastic fuel tanks are very much advanced; they can deform and rebound without failing, thereby maintaining its original volume and safe tank pressure. This prevents the failure of explosion under crash stress.

Emissions: Plastic fuel tanks are permeable to gasoline hydrocarbons. There are certifications in some developed countries for Partial Zero Emission Vehicles (PZEV), which are not provided for vehicles comprising plastic fuel tanks. Ethylene vinyl alcohol (EVOH) is being used as a barrier material in HDPE-based plastic tanks, which lowers the vapor permeability. Regulations set by the US EPA (Environment Protection Agency) and LEV I by CARB (California Air Resources Board) are being met by the plastic fuel tanks using EVOH as a barrier material.

Disposal: Plastic fuel tanks were earlier disposed and caused a major problem to the environment. With current technological advancements, plastic or HDPE-based fuel tanks are recycled. However, technical characteristics are not exactly similar to that of virgin plastic. Regulations in Europe and the US are very stringent in mandating the filing of information regarding the disassembly on every vehicle. These laws require vehicle components to have more than 80% recyclability.

Conclusion

Plastic fuel tanks were traditionally used in internal combustion engine-based vehicles. Presently, hybrid electric vehicles that have an ICE, as well as a battery, also consist of plastic fuel tanks. These plastic fuel tanks help in weight reduction, which is one of the key requirements of the automobile industry. Extended-range electric vehicles are fulfilling the requirement of consumers’ extended range of battery to run electric vehicles for long distances. TI Automotive is the world’s first company to install a plastic fuel tank in an E-REV produced by Karma Automotive. The market attractiveness of E-REVs is expected to increase the consumption of plastics for fuel tanks, globally. The International Energy Agency (IEA) projects the volume of electric vehicles to reach 125 million by 2030.

References:

  1. International Journal of Engineering and Advanced Technology (2014)
    https://www.ijeat.org/wp-content/uploads/papers/v4i1/A3459104114.pdf
  2. General Motors Demonstration Project (1998)
    http://css.umich.edu/sites/default/files/publication/CSS97-01_LCD%20of%20Fuel%20Tank%20Design_EPA600-R97-118.pdf
  3. Plastics Today (2019)
    https://www.plasticstoday.com/automotive-and-mobility/plastic-fuel-tank-plays-key-role-extended-range-electric-vehicle/162721898360144
  4. China Automotive Review (2019)
    https://www.chinaautoreview.com/index.php/ti-automotive-to-supply-double-molded-plastic-fuel-tanks-to-karma-automotives-luxury-ev-program/
  5. Total Plastics Solutions (2017)
    https://www.totalplasticssolutions.com.au/the-benefits-of-plastic-fuel-tanks/
  6. International Journal for Innovative Research in Science & Technology (2015)
    http://www.ijirst.org/articles/IJIRSTV2I5056.pdf