Gasoline volatility and vehicle performance

21 Feb 2012

A six vehicle study has been completed to investigate the impact of changes in the volatility characteristics of unleaded gasoline containing 10% v/v ethanol on regulated exhaust and evaporative emissions and on hot and cold weather vehicle driveability performance. The vehicles selected for this study were representative of the current EU fleet, met or exceeded Euro 4 emissions certification, spanned the range from upper medium to small vehicle classes, were compatible with 10% v/v ethanol according to the manufacturer’s warranty information, and included two modern gasoline Direct Injection Spark Ignition engine types. Results included regulated emissions measured over the New European Driving Cycle (NEDC) at+23°C and -7°C, evaporative emissions according to the European regulatory procedure, cold engine starting and idling at -20°C, and Hot Weather Driveability performance at +40°C.

Unleaded gasolines containing 10% v/v ethanol (E10 gasolines) were specially blended for this study to investigate changes in volatility, specifically in the E701 and E1002 distillation values. The Dry Vapour Pressure Equivalent (DVPE) of all test fuels targeted either summer (60kPa) or winter (100kPa) grade maximum values.The DVPE of the test fuel was selected to be consistent with the type of vehicle test that was completed.

To investigate the impact of volatility changes on vehicle emissions and performance, ‘Baseline’ E10 gasolines were evaluated having E70 and E100distillation values at the current maximum limits allowed by the EN 228 gasoline specification. Results on these ‘Baseline’ gasolines were then compared to fuel shaving relaxed volatility, that is, where the E70 and E100 values were higher than the maximum limits allowed by the EN 228 specification. These volatility values were selected based on a proposal that CONCAWE has made to the European Committee for Standardisation to relax the volatility specifications for future E10gasoline blends.

For most vehicle tests, results on the ‘Baseline’ gasoline were compared to those on a ‘Step 2’ gasoline in which the E70max and E100max specifications were relaxed by+10% v/v and +4% v/v, respectively. Some tests were also conducted on ‘Step 1’gasolines in which the E70max and E100max specifications were relaxed by +4% v/vand +2% v/v, respectively. The ‘Step 1’ gasolines were consistent with CONCAWE’s proposal to CEN for relaxed volatility specifications while tests on the ‘Step 2’gasolines represented a more severe test for vehicle emissions and driveability performance.

All six vehicles were able to complete the required driving cycles on all of the test fuels with no false starts, no misfires, no stalls, no failures, and no faults recorded by the On-Board Diagnostics (OBD) systems. Overall, the impacts of gasoline volatility on emissions and driveability performance were small compared to vehicle-to-vehicle differences.