Vapor Lock Index

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The Vapor Lock Index (VLI, German: volatility index ) is a measure of the quality of motor gasoline calculated from DVPE and E70 . The Dry Vapor Pressure Equivalent (DVPE) is the vapor pressure in kPa of gasoline or gasoline components, measured at 37.8 ° C (corresponds to 100 ° F). The vapor pressure is a measure of how many very light components (e.g. butane , isopentane ) a gasoline contains. If the vapor pressure in the gasoline is too high - especially in summer - these components will outgas. This pollutes the environment and can even be dangerous. E70 (E = evaporated, German: evaporated) is the percentage of gasoline in volume that has evaporated at 70 ° C. It is a measure of the light components ( pentanes , hexanes ) in gasoline.

Vapor pressure and E70 are not independent of each other. A high vapor pressure suggests a high proportion of light substances (pentanes, hexanes), a high E70 also causes an increased vapor pressure. The VLI combines both qualities and represents a measure of the starting and driving behavior when the engine is hot.

The VLI is calculated according to:

VLI = 10 * DVPE + 7 * E70

It is specified for the transition period (October 1st – November 15th and March 16th – April 30th) according to DIN EN 228, ie manufacturers must mix the gasoline in such a way that the specification value of 1150 is maintained. If the DVPE and E70 specifications were to be exhausted at the same time (90 kPa or 50% vol) during the transition period, a VLI of 10 * 90 + 7 * 50 = 1250 would be obtained. That's too high and you either have to lower the vapor pressure or the E70 (or both) to meet the specification.

Excessively high VLI values ​​have a negative impact on starting and driving behavior when the engine is hot due to the formation of vapor bubbles. This is why it is limited by DIN during the critical (transition) period. In summer the vapor pressure is so low (60 kPa, E70 is 48% vol) that a VLI of 936 is not a problem.

literature

  • Richard van Basshuysen, Fred Schäfer: Handbook Internal Combustion Engine Basics, Components, Systems, Perspectives. 3rd edition, Friedrich Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden, 2005, ISBN 3-528-23933-6

Individual evidence

  1. [ Specifications of various gasoline fuels ( memento from August 19, 2012 in the web archive archive.today )]
  2. Engine problems (PDF file; 83 kB)