The effect of gasoline RVP on regulated exhaust emissions has been investigated in a fleet consisting of five current European vehicles. The effects of MTBE with changing RVP and E70 were also studied. All vehicles were equipped with the standard OEM small carbon canisters and three-way catalytic converters and the regulated emissions measured over the new European test cycle. A rigorous refuelling protocol was employed to ensure that the carbon canisters were loaded in a repeatable way before the emission tests.
The results show that a reduction in RVP gave benefits in CO and NOx, but no effect on exhaust THC emissions. The benefits for CO and NOx were greater in non-oxygenated fuels. Of the five test vehicles, three showed CO emission benefits due to RVP reduction, whilst CO from the other two was insensitive to RVP changes. Four vehicles also showed NOx emission benefits due to RVP reduction whilst the NOx emissions from the other vehicle were insensitive to RVP changes. The benefits of reducing RVP were observed for the fleet over all three phases of the cycle, however, the largest percentage changes were seen after the vehicles had warmed up. Although no significant overall effect of RVP on exhaust THC emissions was apparent, reductions in THC over the ECE 3+4 and EUDC phases were observed.
At high RVP MTBE addition gave reductions in CO and NOx emissions, but at low RVP no emission reductions were observed. A reduction in E70 only influenced exhaust THC emissions, resulting in a small increase.