With the price of oil at rock bottom, it seems that no one is interested in biodiesel these days. But don’t think that cheap oil is a long-term solution. At some point, the price of oil will rise and biodiesel will once again be making the news.
Diesel engine fuel systems use fluorocarbon elastomers almost exclusively. Most systems use the traditional Type 1, or copolymer, grade of fluorocarbon like Parker compound VM100-75. It’s the most cost effective of all the fluorocarbons, has excellent compression set resistance, and does a wonderful job with diesel fuel. It’s not as good for low temperature as the low temperature (Type 3) fluorocarbon materials, but diesel fuel and biodiesel both gel at low temperatures, so this limitation doesn’t pose a real-world leakage risk.
Through extensive testing, we’ve found that the “old standby” fluorocarbon compounds do an adequate job in the common 20% biodiesel blends (B20) as long as the application temperature stays below 100°C.
|Material Type||FKM Type 1|
|B20 Biodiesel Blend, 336 hrs. @100°C|
|Hardness Change, pts||-2|
|Tensile Strength Change, %||-19|
|Elongation Change, %||+2|
|Volume Change, %||+4|
However, as the temperature rises and the concentration of biodiesel increases, elastomer compatibility becomes more of a concern. In addition, biodiesel absorbs water and begins to break down over time, and this accelerates the compatibility issues. From our testing, it’s clear that water is a significant “bad actor” when it comes to volume swell. Interestingly, methanol, potassium hydroxide, and higher acidity were not as aggressive to V1164-75.
|Material Type||FKM Type 1|
|Volume Change, %|
|B100, dry, 1008 hrs. @ 125°C||+5|
|B100, wet, (<=5,000 ppm water), 1008 hrs. @125°C||+47|
|B100, wet plus methanol and KOH, 1008 hrs. @125°C||+68|
|B100, rotten (acid number =5), 1008 hrs. @125°C||+23|
The solution is to look at higher performance fluorocarbon compounds. The improved low temperature fluorocarbon compounds also provide much more stability in biodiesel as the temperature increases and as the biodiesel becomes increasingly contaminated. Surprisingly, the GFLT-type of low temperature fluorocarbon (Parker compound V1163-75) did not perform as well as the other low temperature grades.
|Material Type||FKM Type 3||FKM Type 3||FKM Type 3||FKM Type 3|
|B100 plus 1% water, 168 hrs. @125°C|
|Hardness Change, pts.||-30||-9||-4||-21|
|Tensile Strength Change, %||-63||-8||-14||-28|
|Elongation Change, %||-40||+33||+7||-4|
|Volume Change, %||+42||+28||+5||+13|
Of course, these are not the only possible options for use in biodiesel. Other materials may be considered, but they were not evaluated in this particular study.
Low temperature performance
O-rings can typically seal to about 8°C below their TR-10 value in static applications and down to their TR-10 value in dynamic applications. The goal in the diesel engine industry is to seal at -40°C without leakage. To date, that has not been an issue for Type 1 FKMs in diesel and biodiesel applications.
In this case, the best materials for biodiesel in this testing, Parker compounds VG286-80 and V1289-75, also offer improved low temperature performance.
|Type 1 FKM||Type 3 FKM, low swell||Type 3 FKM||Type 3 FKM||Type 3 FKM|
Type 1 fluorocarbon compounds like VM100-75 will continue to be the low cost solution for sealing diesel and biodiesel. In fact, these materials have been used successfully in ongoing multi-year customer field trials without fuel leakage. However, Parker’s low temperature (Type 3) fluorocarbon compounds VG286-80 and V1289-75 offer significant improvements in compatibility with wet and contaminated biodiesel, as well as an additional safety factor for low temperature function.
This article contributed by Dan Ewing, senior chemical engineer, Parker Hannifin O-Ring Division.