The changeover to biofuels increases demands on a vehicle’s fuel system and the various seals contained within.
It seems more and more likely that the use of fossil fuels is heading down a dead-end street. Global warming, rising oil prices and the overwhelming dependency on oil make it a less than viable option for the future.
The introduction of such biofuels as ethanol and biodiesel, with their inherent potential to significantly reduce CO2 emissions, appeared to be the sustainable solution. But the eco-euphoria gave way to alarming reports about the side effects of biofuel production, such as deforestation, rising food prices and even food shortages.
European car manufacturers consider sustainable biofuels an essential part of an integrated approach to reducing CO2 emissions and have invested in engine modifications to accommodate current biofuel blends and future fuel mixes with a higher biofuel content.
A new generation of biofuels
“The second generation of biofuels,” says Gordon Micallef, Technical Director, Trelleborg Sealing Solutions, Malta, “is likely to play an increasingly important role as an energy source for transportation in the near future. These biofuels are made from non-edible feedstock, but also have higher CO2 avoidance potential and increased hectare yields.”
However, these biofuels present new challenges in many areas, from production, to the service station, to the vehicle. “One has to consider their effects on elastomers in fuel and exhaust-gas systems, such as O-Rings used as piston seals. For instance, a blend ratio of 25 percent alcohol in gasoline can cause major deterioration in the properties of elastomers.”
Trelleborg is working on safe alternatives for all types of combustion engines, collaborating with fuel producers and dealers – as well as with customers and original equipment manufacturers. Through testing and compound development, the company is comparing the effects of biofuels on various elastomeric sealing compounds in search of optimal formulations.
Image shows typical seal configuration within a biofuel injector.
Testing reproduced service conditions
“Recently,” Micallef says, “we evaluated the compatibility of typical automotive fuels for both diesel and gasoline engines with various fuel system compounds focusing on hardness, stress-strain and volume swelling. As newer gasoline engines operate at high pressures, the combined effect of high pressures and biofuels was also studied.” The standard laboratory tests suggested that typical elastomers of FKM (Fluorocarbon) and FVMQ (Fluorosilicone) were compatible with the selected biofuels. However, going one step further, testing was conducted to reproduce service conditions.
“This presented a different picture,” Micallef says. “Water contamination in biodiesel is highly probable, which can lead to nonreversible degenerative effects on certain FKMs.”
“In high-pressure gasoline applications,” he continues, “the risk of rapid decompression failure, where gas captured within the seal can cause the seal to split, is increased by the addition of ethanol. In our tests, non-optimized compounds cracked sub-surface. This dramatically reduces the integrity of the seal, while being difficult to detect.”
Crucial to select the right compound
Trelleborg’s tests have proven it crucial to select the right compound for the various seals used in fuel applications.
“Research and development is essential,” says Micallef, “and we are currently working on the next generation of compounds. Our tests show that Trelleborg compounds are superior to non-optimized FKMs in terms of addressing the challenges of biofuel.”
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