Proposed European Rvp limit raises concerns

The EU (European Union) Commission has proposed a constant 60 kPa Reid vapor pressure (Rvp) limit for gasoline specifications in all European countries for the extended summer period of April to September.

Historically, the gasoline Rvp limits were dependent on geography and climate.

An ad hoc group established by Concawe's (Conservation of Clean Air & Water, Europe) Automotive Emissions Management Group concludes that the EU Commission's EU year 2000 Drafts Fuel Directive proposal has several problems.

First, the constant Rvp limit may increase vehicle driveability problems and increase vehicle exhaust emissions in the early and late parts of the extended summer period. The proposed 6-month summer season is too long because summer temperatures vary widely between northern and southern Europe. Second, Rvp reduction can lead to increased hydrocarbon emissions in cold temperatures. Finally, the Rvp limits create in-tank flammability concerns for Nordic countries.

Vehicle evaporative emissions

Predicted total daily losses (TDL) of vehicle emissions for an average European car can be calculated with Rvp and temperature. Concawe calculates that a constant 60 kPa Rvp limit is not required to achieve a maximum loss of 15-20 gpd per European car. Current, EU proposed, and Concawe-proposed Rvp limits for Germany are shown in Fig. 1 [104,459 bytes].

When compared to the U.S., Concawe's proposed limits are low. For reformulated gasoline (RFG), the U.S. averages 9.0 gpd of TDL. EU-proposed limits for TDL average 6.5 gpd, and Concawe proposed limits for TDL average 7.6 gpd.

True vapor pressure (Tvp) best describes potential losses of gasoline during distribution and storage. Tvp is exponentially dependent on temperature and Rvp. Fig. 2 [47,386 bytes] shows that Europe's proposed Tvps during the April to September summer period are similar to or less than that of the U.S.

Cold weather driveability effects

Poor cold weather driveability (CWD), caused by engine misfires or poor combustion, manifests itself in increased hydrocarbon emissions. Because CWD is negatively affected by cold weather, Concawe proposes a higher Rvp limit during cold months. This means shortening the summer period by removing the months of April and September or taking seasonal temperature profiles into account.

Vehicle exhaust emissions

After reviewing three reports (DGMK 513, API 4533, and Concawe report 93/51) to examine the effect of changes in volatility on vehicle exhaust emissions, Concawe makes the following observations:

Lower-Rvp fuels tend to increase hydrocarbon exhaust emissions at temperatures found in European intermediate seasons.
Rvp has no significant effect on CO and NOx emissions.
Rvp has no effect on evaporative emissions for vehicles fitted with an effective control system.

In-tank flammability

When the head space in a gasoline tank is saturated with a vapor above the upper flammability limit, the tank is safe. To prevent tank flammability, fuel storage requires a minimum Rvp, rather than a maximum. Concawe shows that the current proposed winter minimum Rvp limits for Sweden, Finland, and Austria need to be increased 5-10 kPa to prevent formation of flammable liquids in the fuel tank head space. For summer fuel, Scandinavian countries require a minimum Rvp limit close to, or equal to, the EU proposed 60 kPa maximum. Due to the wide temperature ranges in Europe, constant Rvp limits for a 6-month period are not practical, Concawe concludes.