Comments to the Air Resources Board (ARB) of California Concerning LEV III Evaporative Emissions Regulations

SASFT is aware that the test fuel for certifying PZEV evaporative emission levels is being changed from pure gasoline (as specified for LEV II) to a gasoline-based fuel containing 10% ethanol (for LEV III). SASFT understands that the rationale for this change is the wide use of 10% ethanol fuel (E10) by California drivers. Thus, the new test fuel better reflects actual fuel being used by drivers in California. However, SASFT has obtained laboratory test data that suggests that the E10 test fuel is ‘not actual enough’ because it does not include small amounts of water -- a common contaminant in all gasoline-based fuels, but especially in alcohol-containing fuel where the hygroscopic properties of alcohol cause greater absorption of water.

Data developed by SASFT, along with other published data, suggest that the permeation of hydrocarbons through the multi-layer construction of plastic fuel tanks increases as the ethanol level increases, up to about 25% ethanol. Additionally, and more importantly, the permeation rate in low-to-medium ethanol-containing fuels is significantly higher in the presence of small amounts of water. Thus, although PZEV evaporative emission levels may be achievable in HDPE plastic tanks for E10 fuel, higher emissions are to be expected when real world alcohol fuels are used – that is, alcohol fuels that contain small amounts of water. Hence, ARB may be inadvertently drawing the incorrect conclusion that low LEV III evaporative emission levels are being achieved for plastic fuel tank-equipped vehicles using E10 fuels. In reality, because of the normal presence of water contamination in E10 fuels, the actual evaporative emissions levels from the fuel tanks of vehicles equipped with HDPE fuel tanks may exceed, significantly, allowable PZEV levels.

In 2010, SASFT conducted permeation measurements in 40°C isothermal SHED tests for multi-layer HDPE plastic tanks 40% filled with different fuels and soaked at 60°C for 20 weeks. The fuels were Fuel C (no ethanol), ethanol-containing fuels (CE10, CE22, and CE85), and the aforementioned ethanol-containing fuels with the addition of 1% water.

Effect of ethanol and 1% water on the relative permeation (compared with Fuel C) measured in 40°C isothermal SHED tests after 20 weeks exposure of 40% filled production multi-layer HDPE tanks. The results show a significant 146% relative permeation for CE10 (compared to Fuel C), and an even greater 473% relative permeation for CE22 (compared to Fuel C). The fuel with the highest ethanol concentration (CE85) produced 73% of the relative permeation. Of greater significance is the 802%, 536%, and 111% relative permeation measured when 1% water is present in the CE10, CE22 and CE85 fuels, respectively.

In 2007, GTR TEC (Japan) reported a significantly higher level of total permeants in CE10 fuels when 0.1% and 0.5% water was present. The results, shown in Exhibit 2, were obtained using gas chromatography techniques for coupons of HDPE coupons exposed to the fuels at 60°C.

Effect of 0.1% and 0.5% water in CE10 fuel on permeation through HDPE plastic coupons.
Source: GTR TEC, Japan SAE Exposition, May 29, 2007

There is published work reporting that the permeation resistance of EVOH, the widely used permeation barrier in multi-layer HDPE tanks, is affected by fuel composition. In an article in Polymer Testing in 2001, Jose M. Lagaron et al, reported that the permeation rate through EVOH disks was 4 times higher for CE10 compared with 100% gasoline (Fuel C) at 40°C and 12% relative humidity. More important, the authors commented on the effect of water on the barrier performance of EVOH:

EVOH co-polymers generally show poor moisture resistance. The appetite for water of these materials, which results in a high water uptake, leads to deterioration of the gas barrier performance in high relative humidity environments. The deterioration of the barrier properties by moisture uptake derives from the fact that the inter- and intra-molecular hydrogen bonding (so called self association) provided by the hydrogen groups is intercepted by water molecules. This interaction strongly reduces intra-molecular cohesion and mechanical integrity, and increases the fractional free volume of polymer (plasticization effect) for the permeates to travel across polymer packages.”

Source: Jose M Lagaron et al, “Permeation of water, methanol fuel and ethanol-containing fuels in high barrier ethylene-vinyl alcohol co-polymer”, published in Polymer Testing, 20 (2001) pp569-577, Elsevier Press