Fuelled by the need to save weight and reduce evaporative emissions, a great deal of innovative design and materials work is going into vehicle fuel tank systems. Continuing just-auto’s series of interviews with major manufacturers of fuel tanks, Matthew Beecham talked with executives of TI Automotive about trends in tank design, material choices, bio-diesel issues and capless fuel systems.

Generally speaking, what are the factors influencing the design of a fuel tank these days?

The main driver for fuel tank systems designs are the legislative requirements in regards to permeation. In addition, space is at a premium within a vehicle body and it becomes more and more critical to get the space necessary for a fuel tank – meaning fuel tank producers must be more creative when it comes to design.

In addition, components that reduce tail pipe emissions and hybrid vehicles are taking away the space that was traditionally reserved for the fuel tank.

In hybrid vehicles, fuel slosh noise reduction is getting more focus. This is especially needed for start-stop vehicles where the car becomes very silent – while standing at a traffic light for example. 

To address these issues, TI Automotive is developing and producing plastic fuel tanks in complex shapes and sizes, which enables self-damping, reduces emissions and weight and allows for the insertion of slosh walls to reduce noise and improve stiffness in hybrid vehicles.  

While most OEMs show a preference for plastic fuel tanks, am I right in thinking that some have taken a somewhat conservative approach with their initial PZEV vehicle introductions?  How do you see this market unfolding? 

Plastic fuel tanks that meet PZEV requirements are not new. TI Automotive has supplied complex plastic saddle-shaped tanks since 2004 to automakers in Europe and North America. The technical solutions are available, however the real decision about PZEV is related more directly to the market strategy of the OEM.

How do plastic tanks square in Europe given the end-of-vehicle-life requirements?

The end-of-life requirements will not have a significant influence on plastic fuel tanks and the market will continue using them. To meet the recycling requirements in Europe, TI Automotive invested in a recycling programme at the end of the 1990’s, and produced new tanks out of recycled tank material from scrapped vehicles. At that time it was not possible to guarantee a supply chain from old tanks going into the recycling process. 

Given the legislation in Europe and California, can steel tanks really make a comeback? 

The actual legislative requirements will not give a steel tank any benefit against the plastic tank. TI Automotive was always prepared to address new legislation with plastic fuel tanks and has proven this in the market. Considering the CO2 emission, plastic provides a significant benefit in the tank weight compared to a steel tank.

In terms of specification of other architectural parts of the fuel delivery system, such as gauging, venting and feeding, are there any notable trends happening there in terms of technology advances, use of different materials?

Main trends in fuel delivery systems are related to CO2 regulation (e.g. in Europe: 130 g/km in 2015 and potentially 95 g/km in 2020, corresponding respectively to circa 41.3 mpg and 56.5 mpg for gasoline vehicle).

This leads to effort in weight reduction as well as better system efficiency. As a result, brushless pump motors and complex feed pump control systems will begin replacing the current mechanical fuel pressure regulation with brush fuel pump motors.

Additionally, direct injection systems request higher feeding pressure and increased pump performance.

How does the quality of fuel storage affect the design of injection systems? In which countries is this big issue and what are the trends?

The major PC market is currently in Europe. Diesel passenger cars in China are also growing and will become a significant market. Diesel fuel quality in China will be challenging especially in terms of composition stability and sulphur content. However the technical solutions on the fuel pump and the fuel level gauge are already defined for withstanding fuel with high sulphur content. For example, the sealed level sensor is the relevant solution to prevent any impact of the sulphur on the electrical contacts in the level sensor.

Bio-diesel is already popular in Europe and is reported to be spreading to the North American market.  And yet are there still issues concerning the vehicle manufacturers using plastic fuel tanks to store bio-diesel?  Can steel do a better job? What do you see as the issues there?

Bio-diesel had in Germany a unique distribution in the past and was sold as 100 percent bio-diesel. For this application, TI Automotive made plastic fuel tanks 15 years ago which were assembled with special seals and all metallic parts in contact with fuel were replaced by stainless steel parts or other steel types able to handle the fuel. The tank shell was a conventional fluorinated HDPE tank shell at that time. Today, HDPE is performing well with bio-diesel and for the European OEMs, is a state-of-the-art material for this type of tank.

The complete bio fuel actually creates more a problem for metal components and elastomeric parts which are the same within steel tanks, meaning it provides no advantage for steel. As a disadvantage some steel types may face is the corrosion related to storing bio fuels. 
Although biofuels bring a number of benefits, they also present significant engineering challenges. As we understand it, for bioethanol the biggest challenge is the aggressive nature of the fuel in the vehicle tank. Would you agree?

Bio ethanol has absolutely no impact to the plastic fuel tank and for 6 Layer Coex tanks as they are  today – with even no impact on the permeation.  The issues with bio ethanol lies with elastomeric parts and metal parts and from this point of view, remains a bigger issue for steel tanks than for plastic tanks. For plastic tanks the preferred material for seals is FKM which is already in place within the North American market due to lower permeation rates of the material.

On the other hand, biodiesels bring different challenges and may also generate more NOx. Indeed, the challenges presented by biodiesels are significantly different.  Handling and storage is a big issue. Is that correct? In what ways does biodiesel impact on the fuel tank and system?

The statement about the NOx is correct but it will be addressed with the additional SCR systems in the cars. In regards to the bio diesel tanks; there are no additional measures to be taken. Only the elastomeric parts have to be out of FKM. 

As we understand it, BMW is now fitting its incorrect fuelling protection system (IFPS) to all diesel-powered models. Could we expect to see more of this type of mis-fueling technology among other carmakers?

Yes this will be a future trend and other OEM will bring that as well. Especially with the new Diesel injection systems (CDI) the technology is very sensitive and is not good in handling petrol without getting damaged. For the fuel tank system an incorrect fuelling is no problem. 

Capless fuel systems are appearing. Ford has already eliminated the petrol filler cap on certain vehicles.  Again, could we expect to see more capless fuel filler technology appearing?

Capless fuel tank systems have been on the market for many years. Considering the environmental effect, they are continuously under debate. The first drop if you insert the nozzle will go on the outside of the capless system and the same happens to the last, which drops of the nozzle while taking the nozzle out. And if you have fuel on the outside of the cap you have evaporative emissions and even possible draining down to the ground.

On systems with a conventional fuel cap this problem is significantly smaller. In general it is the philosophy of the OEM to go capless or not.