Due to the crucial role of gasoline vapor pressure in evaluating fuel performance and emission risks, the United States Environmental Protection Agency (US EPA) has strict regulations on vapor pressure for petroleum manufacturers. To prevent air resistance and environmental issues, the automotive fuel specification ASTMD4814 requires gasoline to be tested according to ASTM D5188. This standard specifies the evaluation of the gas-liquid ratio temperature. In automotive fuel specifications, the temperature at which the ratio of 20 (steam) to 1 (liquid) is reached (usually referred to as T (V/L)=20) indicates a risk of gas blockage in the fuel. This trend is more pronounced in areas with hot climates and higher altitudes.

As refineries add more and more ethanol to gasoline, and there are increasingly long periods of high temperature weather worldwide, the risk of testing fuels for gas blockage has once again drawn attention. The construction of many older engines simply cannot match modern fuels. In the United States, more and more states are adopting E10 fuel, allowing the addition of 10% ethanol to the fuel. The US Environmental Protection Agency (EPA) often needs to adjust gasoline volatility regulations in the petroleum industry to prevent excessive emissions and ensure driving performance. In the following text, we will also introduce that new cars will also be affected.

The V/L ratio temperature of the test fuel is crucial, mainly because ethanol mixing affects the vapor pressure of the fuel. The vapor pressure of ethanol is much lower than that of gasoline. The addition of ethanol will change the temperature at different V/L ratios. Adding 10% ethanol to gasoline (the current practice in the United States) will greatly reduce the vapor-liquid temperature ratio. Therefore, compared to regular gasoline, gasoline ethanol blends（Ethanol gasoline）At lower temperatures, the critical vapor-liquid ratio that may lead to gas resistance phenomenon will be reached. Figure 1 shows the variation of the vapor-liquid ratio with temperature when different amounts of ethanol are added to gasoline.

It is interesting that the effect of ethanol mixing on vapor pressure is not a linear relationship. Figure 1 shows the abnormal behavior of gasoline ethanol mixture: according to the different V/L ratios, the temperature curve will unexpectedly change direction, rising instead of decreasing. This "S" curve phenomenon is reflected in the mixture of E5 and E10, but not in the mixture of E15. Figure 1 also shows another phenomenon: at low V/L ratios, the T (V/L) of E15 is higher than that of E10 mixture. At a V/L ratio of around 35:1, the two curves intersect, which is caused by the "S" curve phenomenon of E10.

Although these results are surprising, there is no need to worry about blending ethanol into gasoline. But this example demonstrates how important it is to measure not only the fuel at a V/L ratio of 20, but also throughout the entire T (V/L) range, in accordance with the requirements of ASTM D5188, to understand the vapor pressure behavior of modern blended fuels. Testing under the condition of T (V/L)=20, as currently done with ASTM D4814 automotive fuel specifications, cannot provide sufficient information about fuel vapor behavior. This example also shows that according to the current practice, adding a higher proportion of ethanol into gasoline may make the performance of the mixed fuel more predictable.

The phenomenon of air resistance is also an increasingly severe challenge for car manufacturers, who are developing new engines that must be able to use different fuels. When modern jet engines stop after prolonged driving, some may not be able to restart immediately. The reason is that the temperature of these new engines is as high as 120-140 ° C, and air resistance is prone to occur at high temperatures. Especially when using new hybrid fuels, air resistance issues become more frequent. Recent feedback from car manufacturers indicates that they particularly need to test vapor pressure testing equipment up to 5-6 Bar and closely monitor vapor pressure data when developing new generation engines.

AustriaGrubnerGrabner asThe expert in vapor pressure measurement has developed a widely used MINIVAP VP Vision fully automatic micro vapor pressure tester for evaluating temperature at different V/L ratios in ASTM D5188 testing. MINIVAP VP Vision is still the best solution for testing the vapor pressure of ethanol gasoline at high temperatures. It can perform multi-point curve measurements up to 120 ° C and is the highest temperature range vapor pressure gauge on the market. This instrument adopts the world-renowned GRABNER micro method and three-stage expansion method for vapor pressure testing, which meets all industry vapor pressure testing standards. Therefore, it can safely develop a new generation of automotive engines using ethanol blended fuels.