Impact of Ethanol Fuel Blends on Automatic Tank Gauging

Audio version
Posted / Last update: 14-06-2011
Publication: PetrolPlaza Technology Corner
Issued: May 2011
Author: Frey Ulrich, Hectronic GmbH
  • Figure 2: Magnetostrictive gauges with moving floats

E85 and E100 do not build a separated water phase, however, the challenge is how to measure the water/ethanol phase of E10 or other fuel blends at the tank bottom.

For technical reasons all types of probes do not detect a level less than about 20 mm. Is it possible to detect changes by measuring the density? Gasoline has a density of typically 720 - 775 kg/m³ (according to DIN EN 228), ethanol has typically 790 kg/m³. E10 does not mean exactly 10%, but something between 5.6% up to 10% ethanol. Changes in density of the fuel phase caused by variation of the ethanol part are much lower than the general allowed variation of gasoline density and vanish completely within this bandwidth.

Measuring the density of the water/ethanol phase would be complicated and do not provide more information than already known by measuring the level. So density is not the right method.

There are mainly two types of tank gauges in the petrol market

  • magnetostrictive gauges with moving floats
  • gauges without any moving parts measuring the capacitance.

Magnetostrictive gauges usually have two floats, one for the fuel (1) and one for the water phase (2); see figure 2.

The water float must be heavier than fuel and lighter than water to float on the interface. If the float is only a little bit heavier than the medium then there is no buoyancy anymore.

Ethanol present in the water phase reduces the density of the mixture. If the water float (2) is now only a little heavier than the water/ethanol mixture there is no longer any buoyancy and the float will sink down to the bottom of the tank instead of floating on the interface. In this case existing water is no longer detected.

Another problem may occur when a second skin is drawn into the tank to retrofit a double-wall leak inspection. The skin is fixed with magnets to the inner side of the tank wall. Because of ethanol special material and stronger magnets may be needed for the skin. The magnetic field of the stronger magnets may influence the water float and cause false alarms.

Gauges with capacitive measurement do not suffer the same problems. Instead they continue to work with the same accuracy, independent from magnetic fields or density of the water/ethanol phase. Capacitance gauges are able to detect the separated phase even for ethanol blends up to E25 without the need to change any parts.

When using capacitance technology you can be sure that level and interface will always be measured accurately for all type of ethanol blended fuels.

Frey Ulrich, Hectronic GmbH
Ulrich Frey is the Business Unit and Development Manager for Sensor Systems at Hectronic GmbH, Bonndorf Germany. Ulrich Frey has a Diploma in Precision Engineering and uses his extensive experience to develop intelligent solutions for modern content management at petrol stations.

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