Research on the Material Compatibility of Elastomer Sealing O-Rings

Significant attention has been paid to combustion engines for the utilization of new liquid fuels and their testing at the present. Research activities in ensuring the optimum function of the engine by watching sealing and distribution rubber elements, which are part of fuel systems, should be an integral part of fuels research. When evaluating fuels utilization in combustion engines, the issue has to be judged in a complex. However, when using biofuels in combustion engines, it is not always simple owing to the different degradation properties of these products. Elastomer material is not entirely resistant to various types of fuels. More or less, it is possible to expect changes in its mechanical properties. For the evaluation of the functionality of elastomer sealing elements based on ACM, HNBR and FVMQ type O-rings with pure and blended fuels, the evaluation of changes in mass, hardness Shore A, permanent deformation CS, tensile strength TS and deformation Eb after immersion with the tested fuel is mainly used. Permanent changes were found by the tests. The degradation of elastomer O-rings was more pronounced for the tested fuels containing ethanol, iso-butanol, n-butanol, methanol and dodecanol. HVO 100 fuel containing hydrotreated vegetable oil did not show significant degradation of elastomer O-ring seals. Of the O-rings tested, the FVMQ type O-rings showed the best performance in terms of material compatibility for all fuels tested.


Introduction
There is a huge number of elastomer materials that can be used in fuel systems. The producers of these elastomer seals define the options and limits of their applications. New elastomer materials for a certain application, namely, composite-based nanoparticle fillers, have been constantly developed [1,2]. Although many decades have passed since the first practical application of the vulcanization of rubber, intensive research in the area of sophisticated methods affecting the chemical process of vulcanization is still underway [3]. Conclusions from computer-aided design and associated mathematical modeling are particularly important for practical applications, especially among manufacturers [3,4].
Significant research has been conducted on the options of new biofuels and their various combinations in the field of fuels. These research activities influence the properties and emissions of combustion engines. It is necessary to not forget the weak points of these engines, and they are elastomer seals and fuel tubes which can have, in the case of the damage or the deterioration of mechanical properties, major consequences for the whole car. So, the development of reliable, high-performance elastomer materials will continue to play a key role in developing new emission-decreasing fuels [1]. be expected in the future [18]. However, these fuels and their various combinations can aggressively act as elastomer seals and distribution tubes of fuel systems [1]. So, it is necessary to determine which changes can occur in the long term, which generally increase the degradation of the elastomer material [12,16]. It is necessary to determine the compatibility of elastomer elements exposed to the influence of liquid biofuels in combustion engines with an emphasis on their service life and on keeping the required mechanical properties.
The degradation of rubber materials in biofuels is caused by the presence of various additives in biofuels and rubber blends, oxidation and rubber damage [19].
In an automotive system, a number of modular units, such as the fuel pump, the fuel injectors, the engine and the exhaust system, are in direct contact with the fuel and the sealing rubber element [19]. Since conventional automotive fuel systems have been adapted to petroleum-based fuels, switching to biofuels can potentially cause the swelling and degradation of the rubber [20].
Research shows that the most significant deterioration is in rubber materials compared to various metals and their alloys, which causes swelling and degradation, particularly of O-rings [21].
The compatibility of individual elastomer materials (abbreviations according to ISO 1629) and the resistance to liquids that can be used in the automotive industry are presented in Table 1 [11]. However, the authors of this publication state that the presented resistance and compatibility values of individual elastomer materials are orientations, and they always have to be experimentally verified because of the various physical aspects of a specific application in the fuel system [11]. However, it is possible to regard this table as a basic presumption narrowing the selection of tested materials. The aim of this research was the long-term monitoring of the compatibility of elastomer O-ring-based seals with pure and blended fuels and the associated definition of mechanical tests, i.e., the material compatibility of elastomer seals and fuel was evaluated on the basis of permanent deformation CS, tensile strength TS, elongation Eb, hardness Shore A and mass.

Materials and Methods
The material compatibility of the elastomer seal (sealing O-rings) and the fuel is tested over a time interval of 2998 h (approx. 4.2 months, 125 days), which is determined in accordance with ASTM D471-16 (Standard Test Method for Rubber Property Effect of Liquids).
According to the supplier's specification, the O-rings made from ACM are highly resistant against oils with a high temperature; they are used in the automotive industry for sealing the engine and for gearbox oil and other high-temperature lubrication systems. The ACM O-rings have a temperature range from −20 to 175 • C. The O-rings made from HNBR are highly resistant against mineral oils with additives, and their temperature range is from −20 to 150 • C. The O-rings made from FVMQ are highly resistant to oils, fuels and solvents, especially aromatic and chlorinated hydrocarbons and alcohols; their temperature range is from −60 to 200 • C.
The test fuels that were used in the tests aimed at influencing the chemical resistance and compatibility of the elastomer materials defined in Table 2. Since ethanol and methanol are insoluble in diesel, it is necessary to use co-solvents in order to prevent a phase separation. Iso-butanol and dodecanol were used as the co-solvents. For 5% blends, only iso-butanol was used; for 10% blends, the use of the combination of iso-butanol and dodecanol was necessary, especially for methanol. For fuel blends with n-butanol, no co-solvent was used, as there are no solubility problems with n-butanol in diesel, and no phase separation was observed.
Specifications of the test fuels and their base components are shown in Table 3. The fuel density and kinematic viscosity were determined by means of the Stabinger Viscometer SVM 3000 from Anton Paar GmbH (measurement accuracy < 1%, repeatability = 0.1%).
The calorific values of the base fuels were determined using the isoperibol calorimeter LECO AC600 (range 23.1-57.5 MJ/kg for a 0.35 g sample, accuracy 0.1% RSD) according to CSN DIN 51900-1 [22] and CSN DIN 51900-2 [23]. The mass contents of the carbon, hydrogen and oxygen of the alcohols were calculated based on the atom masses of the atoms in their molecule. For diesel, the content is given by EN 590, and for HVO, it is given by EN 15940. The C, H and O contents of the fuel blends were calculated based on the mass concentration of the individual alcohols in the blends, which was determined using the measured densities of the base fuels and their volumetric concentrations.
The material compatibility of the elastomer seal and the fuel was evaluated based on permanent deformation CS (%), tensile strength TS (MPa), elongation Eb (%), hardness Shore A SHA and mass before and after immersion in the tested fuel. Material compatibility measurements after the removal of the O-rings from the test fuels were performed after the evaporation of the volatile fuel in accordance with ASTM D471-16, which was determined by stopping the mass loss of the samples on the analytical scales.
The measurements of permanent deformation CS (%), tensile strength TS (MPa) and elongation Eb (%) were carried out on the electromechanical testing machine MPTest 5.050 of the Czech company LaborTech. According to EN 7500-1, the device meets the requirements for class 0.1. The accuracy of the force gauge used is 0.1 N; the position of the crossbar is detected with an accuracy of 0.001 mm.
The permanent deformation-compression set is another essential parameter for determining the sealing properties of the elastomers in the fuel systems. The fact that pressing causes not only their elastic deformation but also their plastic deformation is a reason for this. The permanent deformation CS can considerably differ owing to the degradation acting of the liquid contaminant fuels.
The permanent deformation CS was measured according to the modified standard CSN ISO 815-1 (Rubber, vulcanized or thermoplastic elastomer-Determination of permanent deformation in compression-Part 1: At laboratory or elevated temperatures). The research results of Muller et al. [6] proved the possibility of testing O-rings from the fuel system. The modification of the standard consisted in the use of real sealing rings and the loading time. The measurement of the permanent deformation of the O-rings can be seen in Figure 1A.
hardness Shore A of the O-rings can be seen in Figure 1D. Figure 1 shows the testing of the initial mechanical properties of the O-rings and the properties after a specified time of 2998 h after their immersion in the tested fuels. The material compatibility of the elastomer seal and fuel based on permanent deformation CS (%) can be seen in Figure 1A; the tensile strength TS (MPa) can be seen in Figure 1B; the elongation Eb (%) can be seen in Figure 1 B; the mass can be seen in Figure 1C; the hardness Shore A SHA can be seen in Figure 1D. The change in the mechanical properties of permanent deformation CS (%), tensile strength TS (MPa), elongation Eb (%), hardness Shore A SHA and mass before and after immersion in the tested fuels is calculated as a percentage change and is in accordance with ASTM D471-16.
The percentage change in mass ΔM was calculated using Formula (5), where: ΔMchange in mass (%), M0-initial mass of the O-ring specimen in air before immersion in the fuel (mg), M1-mass of the O-ring specimen in air after immersion in the fuel (mg).
The change in hardness ΔH after immersion is given in units of hardness and is calculated according to Formula (6), where: ΔH-hardness change after immersion (ShA), H0-initial hardness of the O-ring specimen in air before immersion in the fuel (ShA), H1hardness of the O-ring specimen in air after immersion in the fuel (ShA).
The percentage change in tensile strength ΔTS was calculated according to Formula The permanent deformation CS can be calculated according to Equation (1), where: CS-permanent deformation-compression set (%), h 0 -initial height of the O-ring (mm), h 1 -height in the state of compression (mm), h 2 -height after release (mm).
The tensile strength TS and the elongation Eb can be determined in accordance with the standard. The tensile properties of the rubber were determined according to the modified standardČSN ISO 37 (Rubber, vulcanized or thermoplastic elastomer-Determination of tensile properties). The modification consisted in testing real fuel seals. The modification of real products determined for the fuel systems was proved by the scientific studies of Muller et al. [6]. For example, the authors recommend using hooks for O-rings clamping to prevent damage of the surface integrity and decreases in the tested material strength.
The tensile strength TS can be calculated according to Equation (2), where: TS-tensile strength (MPa), F m -maximum tensile force (N), h 0 -initial height of the O-ring (mm).
The elongation E b can be calculated according to Equation (3), where: The initial inner circumference of the O-ring C j was calculated from the inner diameter of the O-ring, which was determined from the distance of the hooks during the tensile test, when the measured force started to increase. The final inner circumference of the O-ring C b was calculated from Formula (4), where 2.9 mm is the hook wire diameter.
where: C b -final inner circumference of the O-ring (mm), L b -distance of the hooks when the O-ring breaks (mm). The tensile strength and elongation measurements of the O-rings can be seen in Figure 1B. The initial mass of the specimen (sealing O-rings) in air and the mass of the specimen in air after the immersion in the tested fuel were determined by weighing on KERN analytical scales. The measurement of the mass of the O-rings can be seen in Figure 1C.
The hardness is the most often tested mechanical quantity of elastomer materials. The hardness can be defined as the body resistance to the penetration of another harder body (indenter) into a tested surface. However, the measurement of the elastomer material hardness is a problem owing to the thickness of the tested material. The standard CSN EN ISO 868 states a minimum value of 4 mm for the Shore A method. It is suitable to use this method (Shore A) for elastomer seals because it is determined for soft to medium-hard elastomer materials. It is possible to solve this problem by layering several elastomer materials on top of each other, which the standard enables. The authors Muller et al. introduced a special device for testing layered O-rings hardness [6]. The measurement of the hardness Shore A of the O-rings can be seen in Figure 1D. Figure 1 shows the testing of the initial mechanical properties of the O-rings and the properties after a specified time of 2998 h after their immersion in the tested fuels. The material compatibility of the elastomer seal and fuel based on permanent deformation CS (%) can be seen in Figure 1A; the tensile strength TS (MPa) can be seen in Figure 1B; the elongation Eb (%) can be seen in Figure 1B; the mass can be seen in Figure 1C; the hardness Shore A SHA can be seen in Figure 1D.
The change in the mechanical properties of permanent deformation CS (%), tensile strength TS (MPa), elongation Eb (%), hardness Shore A SHA and mass before and after immersion in the tested fuels is calculated as a percentage change and is in accordance with ASTM D471-16.
The percentage change in mass ∆M was calculated using Formula (5), where: ∆M-change in mass (%), M 0 -initial mass of the O-ring specimen in air before immersion in the fuel (mg), M 1 -mass of the O-ring specimen in air after immersion in the fuel (mg).
The change in hardness ∆H after immersion is given in units of hardness and is calculated according to Formula (6), where: ∆H-hardness change after immersion (ShA), H 0 -initial hardness of the O-ring specimen in air before immersion in the fuel (ShA), H 1 -hardness of the O-ring specimen in air after immersion in the fuel (ShA).
The percentage change in tensile strength ∆TS was calculated according to Formula (7), where: ∆TS-change in tensile strength (%), TS 0 -initial tensile strength of the O-ring specimen in air before immersion in the fuel (%), TS 1 -tensile strength of the O-ring specimen in air after immersion in the fuel (%).
The percentage change in elongation ∆Eb was calculated according to Formula (8), where: ∆Eb-change in elongation (%), Eb 0 -initial elongation of the O-ring specimen in air before immersion in the fuel (%), Eb 1 -elongation of the O-ring specimen in air after immersion in the fuel (%).
The percentage change in permanent deformation ∆CS was calculated according to Formula (9), where: ∆CS-change of permanent deformation (%), CS 0 -initial permanent

Results and Discussion
The compatibility of the tested fuels and their blends with the ACM, HNBR and FVMQ O-rings was investigated based on changes in the mechanical properties of permanent deformation ∆CS, tensile strength ∆TS, elongation ∆Eb, hardness Shore A ∆H and mass ∆M.
Higher initial values of permanent deformation CS are exhibited by the ACM (0.13 ± 0.01) and HNBR (0.14 ± 0.01) O-rings compared to FVMQ (0. 10 Figure 2 shows the change in mass ∆M for different elastomer O-rings and fuels after exposure for a time interval of 2998 h. Figure 2 shows the increase and decrease in the mass of elastomer O-rings after exposure in different types of fuels. air before immersion in the fuel (%), Eb1-elongation of the O-ring specimen in air a immersion in the fuel (%).
The percentage change in permanent deformation ΔCS was calculated according Formula (9), where: ΔCS-change of permanent deformation (%), CS0-initial perman deformation of the O-ring specimen in air before immersion in the fuel (%), CS1-perm nent deformation of the O-ring specimen in air after immersion in the fuel (%). ∆ = ( − ) . 100

Results and Discussion
The compatibility of the tested fuels and their blends with the ACM, HNBR a FVMQ O-rings was investigated based on changes in the mechanical properties of perm nent deformation ΔCS, tensile strength ΔTS, elongation ΔEb, hardness Shore A ΔH a mass ΔM.
Higher initial values of permanent deformation CS are exhibited by the ACM (0.1 0.01) and HNBR (0.14 ± 0.01) O-rings compared to FVMQ (0.10 ± 0.01), while ten strength TS is exhibited by the HNBR O-rings ( Figure 2 shows the change in mass ΔM for different elastomer O-rings and fuels a exposure for a time interval of 2998 h. Figure 2 shows the increase and decrease in mass of elastomer O-rings after exposure in different types of fuels. The results show that the FVMQ sealing O-ring has good compatibility with the tested fuels in terms of mass loss. There was change in mass ∆M ranging from −1.5% to 3%. The change in mass was almost constant compared to the other materials tested, which showed a change in mass ∆M of −9.7% to 32.4%.
On the other hand, the O-rings made of ACM and HNBR are less compatible. The results show a high mass loss for the fuel M100 at the HNBR O-rings. Conversely, the results show a high mass gain at the ACM O-rings in the fuels M5 ISO BUT, E100, E10 2.5DOD 6Isobut and M10 2.5DOD 6Isobut.
The swelling of the O-rings can be represented by changing their mass and the initial mass of the O-ring specimen in air before immersion in the fuel to the mass of the O-ring Polymers 2022, 14, 3323 9 of 14 specimen in air after immersion in the fuel [33]. An increase in mass after the degradation process was observed for the ACM and HNBR O-rings, except for the fuel M100, where there was a decrease in the mass of the O-ring specimen in air after immersion in the fuel from HNBR. From the results, it can be concluded that the fuel HVO had a minimal effect on the change of all three O-ring materials tested. In general, the increase in mass is related to the swelling of elastomers, which is caused by an absorption of the fuel into the polymer chains [34].
The influence of the change in mechanical properties is evident from the other figures, i.e., hardness Shore A ∆H (Figure 3), tensile strength ∆TS (Figure 4), elongation ∆Eb ( Figure 5) and, last but not least, permanent deformation ∆CS (Figure 6). Figure 3 presents the change in hardness Shore A ∆H for different elastomer O-rings and fuels after exposure for a time interval of 2998 h. Figure 3 presents the hardness Shore A loss of elastomer O-rings after exposure in different types of fuels. The HVO fuel, which did not show a decrease in hardness Shore A, exhibited a different behavior among the tested fuels. On the other hand, there was a slight increase of 11.32% for the ACM sealing O-rings and of 0.96% for the HMBR sealing O-rings. For the elastomer O-rings of type FVMQ, which were tested last, there was a slight decrease in hardness not exceeding 1%.
The results show that the FVMQ O-ring has good compatibility with the tested fuels in terms of eliminating significant variations in hardness at the interval of −8.42 to 1.08%. Figure 3 shows significant changes in hardness Shore A approaching 35%. Hardness reduction is also presented by other researchers in their publications on the compatibility of different elastomers with diesel and different biodiesel blends [33,35]. Carbon black and silica fillers, which primarily serve to improve hardness and tensile properties, can be considered as the cause of the hardness decrease in various biofuels. These components can react with biofuels after a certain exposure time and, secondarily, can deteriorate the above-mentioned properties [33].
Polymers 2022, 14, x FOR PEER REVIEW 9 The results show that the FVMQ sealing O-ring has good compatibility with tested fuels in terms of mass loss. There was change in mass ΔM ranging from −1.5 3%. The change in mass was almost constant compared to the other materials te which showed a change in mass ΔM of −9.7% to 32.4%.
On the other hand, the O-rings made of ACM and HNBR are less compatible results show a high mass loss for the fuel M100 at the HNBR O-rings. Conversely results show a high mass gain at the ACM O-rings in the fuels M5 ISO BUT, E100 2.5DOD 6Isobut and M10 2.5DOD 6Isobut.
The swelling of the O-rings can be represented by changing their mass and the i mass of the O-ring specimen in air before immersion in the fuel to the mass of the O specimen in air after immersion in the fuel [33]. An increase in mass after the degrad process was observed for the ACM and HNBR O-rings, except for the fuel M100, w there was a decrease in the mass of the O-ring specimen in air after immersion in the from HNBR. From the results, it can be concluded that the fuel HVO had a minimal e on the change of all three O-ring materials tested. In general, the increase in mass is re to the swelling of elastomers, which is caused by an absorption of the fuel into the poly chains [34].
The influence of the change in mechanical properties is evident from the othe ures, i.e., hardness Shore A ΔH (Figure 3), tensile strength ΔTS (Figure 4), elongation ( Figure 5) and, last but not least, permanent deformation ΔCS ( Figure 6). Figure 3 presents the change in hardness Shore A ΔH for different elastomer Oand fuels after exposure for a time interval of 2998 h. Figure 3 presents the hardness S A loss of elastomer O-rings after exposure in different types of fuels. The HVO fuel, w did not show a decrease in hardness Shore A, exhibited a different behavior amon tested fuels. On the other hand, there was a slight increase of 11.32% for the ACM se O-rings and of 0.96% for the HMBR sealing O-rings. For the elastomer O-rings of FVMQ, which were tested last, there was a slight decrease in hardness not exceeding  above-mentioned properties [33]. Figure 4 shows the change in tensile strength ΔTS for different elastomer O-rings fuels after exposure for a time interval of 2998 h. From the results, it is clear that al all the tested fuels and elastomer O-rings lose tensile strength TS in the interval from to −3.9%. Smaller changes in tensile strength TS can be observed for fuel HVO100 three sealing elastomer O-rings. However, the FVMQ sealing O-rings showed sm changes compared to the ACM and HNBR sealing O-rings. There was a slight increase in tensile strength TS of 4.0% for elastomer O-rin type ACM placed in HVO 100 fuel.
Significant changes in tensile strength TS exceeding 60% were exhibited by s fuels, as can be seen in Figure 4-particularly, fuels designated as E100, E10 2.5DOD, but and M10 2.5DOD 6Isobut and elastomer O-rings of the ACM and HNBR types.
This was an approximately similar trend of changes in ∆TS as the trend in the lo hardness ∆H (ShA), which has been referred to in other papers focusing on simila search [36]. Figure 5 shows the change in elongation ΔEb for the different elastomer O-rings fuels after exposure for a time interval of 2998 h. The results show a decrease in elong ΔEb for all of the tested fuels for the elastomer FVQM O-ring and for most of the te fuels, except for HVO100, D100 and E10 2. 5DOD 6Isobut, for elastomer O-rings of HNBR. A significant increase in elongation ΔEb was found for almost all of the te fuels, except for the fuel BUT 100 (decrease of −1.3%), for elastomer O-rings of type A In particular, these O-rings showed a significant change in shape and elongation ΔE up to about 40%, which did not allow for their possible use. These results correspond significant change in ΔM.   [37]. An increase in the permanent deformation ΔCS values occurred for the HVO 100 at all three elastomer sealing O-rings. Furthermore, an increase in the perma deformation ΔCS value occurred at the elastomer O-rings of type FVMQ for the BUT100, M100 and E100.

Conclusions
From the obtained results, it is possible to draw the following conclusions related the monitoring of the long-term compatibility of elastomer seals based on O-rings of t ACM, HNBR and FVMQ with pure and blended fuels.

•
The mass change due to the effect of the tested pure and blended fuels was mini for the FVMQ type O-rings. The values were almost constant, with the chang mass ΔM ranging from −1.5% to 3%. The change in mass was more pronounced the ACM and HNBR O-rings, with a change in mass ΔM of −9.7% to 32.4%. These rings are less compatible with the fuels tested. Significant changes in tensile strength TS exceeding 60% were exhibited by some fuels, as can be seen in Figure 4-particularly, fuels designated as E100, E10 2.5DOD, 6Isobut and M10 2.5DOD 6Isobut and elastomer O-rings of the ACM and HNBR types.
This was an approximately similar trend of changes in ∆TS as the trend in the loss of hardness ∆H (ShA), which has been referred to in other papers focusing on similar research [36]. Figure 5 shows the change in elongation ∆Eb for the different elastomer O-rings and fuels after exposure for a time interval of 2998 h. The results show a decrease in elongation ∆Eb for all of the tested fuels for the elastomer FVQM O-ring and for most of the tested fuels, except for HVO100, D100 and E10 2. 5DOD 6Isobut, for elastomer O-rings of type HNBR. A significant increase in elongation ∆Eb was found for almost all of the tested fuels, except for the fuel BUT 100 (decrease of −1.3%), for elastomer O-rings of type ACM. In particular, these O-rings showed a significant change in shape and elongation ∆Eb of up to about 40%, which did not allow for their possible use. These results correspond to a significant change in ∆M. Figure 6 shows the change in permanent deformation ∆CS for different elastomer sealing O-rings and fuels after exposure for a time interval of 2998 h. From the experimental results shown in Figure 6, it is clear that different fuels mostly reduce the permanent deformation of O-rings. The sealing elastomer O-rings were more elastic. Considering the function of the sealing O-rings, this is a positive effect. The literature on rubber sealing elements indicates that larger permanent deformation values are significantly negative [37]. An increase in the permanent deformation ∆CS values occurred for the fuel HVO 100 at all three elastomer sealing O-rings. Furthermore, an increase in the permanent deformation ∆CS value occurred at the elastomer O-rings of type FVMQ for the fuels BUT100, M100 and E100.

Conclusions
From the obtained results, it is possible to draw the following conclusions related to the monitoring of the long-term compatibility of elastomer seals based on O-rings of type ACM, HNBR and FVMQ with pure and blended fuels.

•
The mass change due to the effect of the tested pure and blended fuels was minimal for the FVMQ type O-rings. The values were almost constant, with the change in mass ∆M ranging from −1.5% to 3%. The change in mass was more pronounced for the ACM and HNBR O-rings, with a change in mass ∆M of −9.7% to 32.4%. These O-rings are less compatible with the fuels tested. In particular, the HNBR type O-rings, and especially the ACM type O-rings, experienced significant losses, especially for the fuels M100, M5 ISO BUT, E100, E10 2.5DOD 6Isobut, M10 2.5DOD 6Isobut and E10 ISO BUT. • Permanent changes were found when evaluating the elastomer O-rings. Mechanical tests of hardness Shore A, tensile strength TS, elongation Eb and permanent deformation CS focused on the changes in their material compatibility in different fuels. The changes in hardness Shore A were mostly manifested by a decrease in their hardness due to time and the exposure to the tested fuels. Only the fuel HVO 100 showed a significant increase in hardness Shore A values. In terms of the tested elastomer rings, the FVMQ type O-ring was shown by measurements to have good compatibility with the fuels tested in terms of eliminating significant variations in hardness changes in the interval from −8.42 to 1.08%. A similar trend of behavior was observed for the tensile strength TS results. From the results, it is clear that almost all of the tested fuels, except for HVO 100 and the elastomer rings ACM, HNBR and FVMQ, lose tensile strength TS in the interval from −60.4 to −3.9%. Again, the tensile strength TS results showed that the FVMQ O-rings showed less of a change compared to the ACM and HNBR O-rings. The results also showed a significant effect on the change in elongation ∆Eb. In particular, elastomer O-rings of the ACM type showed a significant change in shape, and their elongation ∆Eb changed up to about 40%. This significant change would not allow for their possible use in a fuel system. The fuels tested also had a significant effect on the changes in permanent deformation ∆CS for the different elastomer O-rings, with a reduction in permanent deformation in most tests.

•
The degradation of elastomer O-ring seals was also more pronounced for fuels containing ethanol, iso-butanol, n-butanol, methanol and dodecanol. The fuel HVO 100 contains hydrotreated vegetable oil, which did not significantly affect the degradation of elastomer O-ring seals. Of the O-rings tested, the FVMQ type O-rings showed the best performance in terms of material compatibility and the dependence on the fuels tested.