An analysis of hot weather-driveability performance of the year 2000 European Union (EU) car population makes a vapor lock index (VLI) no longer necessary for summer 2000 volatility classes.
For nonsummer periods, only four markets (Finland, France, Greece, and Portugal) require a VLI for good performance during transition between summer and winter.
These are the recommendations of Concawe to the European Standardization Committee (CEN) for the 2000 revision of the EN228 gasoline specifications, established in 1993. Concawe (Conservation of Clean Air & Water, Europe), Brussels, describes itself as the oil companies' European organization for environmental and health protection. It presented its proposals of revised volatility classes in a report published in January 1999.
These revisions are driven by the new EU Fuels Directive (98/70/EC) scheduled to go into effect in 2000. The directive changes the volatility characteristics of fuels in 2000. In particular, olefins, aromatics, and benzene restrictions will require changes in refinery processing and a need for increased use of lower-boiling blending components, such as isomerate and MTBE.
As a result of these year 2000 changes to gasoline, hot-weather driveability will be constrained by the maximum E70 (percentage of fuel evaporated at 70° C.) limit. In the report, Concawe examined the relaxation of Rvp, E70, or VLI limits in each EU country to allow for good hot-weather driveability.
Customer satisfaction
Concawe generated customer-satisfaction curves of hot-weather driveability for 14 European markets for the relevant months to allow for appropriate selection of volatility classes. These markets were Austria, Benelux, Denmark, Finland, France, Germany, Greece, Italy, Norway, Portugal, Spain, Sweden, Switzerland, and the U.K.
Its predictions of customer satisfaction are based on a database of hundreds of vehicles tested over many years and representing a variety of engine technologies, including carburetted, multipoint injection, and single-point injection.
In general, as carburetted engines are replaced with electronically fuel-injected ones, hot-weather driveability will no longer be a problem. Modern vehicles are very tolerant of hot conditions and high-volatility fuels.
Until all carburetted engines are replaced, however, a balance between maximum ambient temperature and fuel volatility is required to avoid hot weather driveability malfunctions. Mismatches can lead to vaporization of gasoline in the engine, which cause problems because instruments in the engine may be unable to deal with vapor.
Current and proposed specs
Table 1 shows the current CEN volatility specifications. Eight volatility classes are included in the EN 288 specification, and CEN member countries can choose up to three classes to cover their climatic variations.
Hot weather performance is controlled by limits to the VLI. (VLI = Rvp(kPa)*10 + 7*E70.)
The new EU Fuels Directive for 2000 (98/70/EC) specifies Rvp at a much lower level than current EN 288 specs. It specifies a maximum Rvp of 60 kPa for the summer period, which begins no later than May 1 and ends after Sept. 30.
For markets with arctic conditions, Rvp will be limited to 70 kPa for a summer period beginning no later than June 1 and ending after Aug. 31 (a minimum of 3 months).
Proposed summer revisions to the EN 288 specs are shown in Table 2a. Nonsummer revisions are shown in Table 2b.
For the year 2000 summer volatility classes, VLI is no longer necessary because the Rvp limits of 60 and 70 kPa already ensure total customer satisfaction. Fig. 1 shows that for France, the proposed volatility box remains within the satisfaction of 1997 and 2000 fleets.
For other seasons, VLI is generally no longer necessary either, except for Finland, France, Greece, and Portugal. Fig. 2 shows that for France, for nonsummer Class D, the months of October and April will not be within customer satisfactory performance. For these four countries, alternative solutions are required.
To accommodate the use of lower-boiling blending streams to meet lower limits on olefins, aromatics, and benzene, Concawe suggests raising the maximum E70 limit to 48 vol % for summer classes and to 50 vol % for nonsummer classes.
As Fig. 2 shows for France, this does not compromise customer satisfaction. Charts for the other 13 market areas show similar trends.
Minimum Rvp specifications have been increased to reduce the possibility of tank vapor-space flammability during cold spells. Also, higher maximum E100 specifications have been proposed to compensate for some changes in the EU Fuels Directive.
