report no. 8/09

21 Oct 2009

The effect of blending ethanol (up to 20% v/v) into gasoline on the volatility of theethanol/gasoline blend and on the hot and cold weather vehicle driveabilityperformance of these blends has been assessed from published literature. Thisliterature review covers major fuel blending and vehicle driveability studies that havebeen completed over the past 20 years. Volatility of Ethanol/Gasoline Blends The percentage of an ethanol/gasoline blend that evaporates at 70oC (E70)substantially increases when ethanol is blended into gasoline. The correspondingE100 (the percent of the blend that evaporates at 100oC) also increases but lesssubstantially than the E70 value. The increase in these two volatility parameters withethanol addition is usually smaller as the volatility of the gasoline increases.Interestingly, “Blending E70” values for ethanol tend to decrease with increasingethanol content while “Blending E100” values increase. This difference is due to theformation of an azeotrope that affects the volatility behaviour of the ethanol/gasolineblend at different temperatures. Simple predictive models have been developedbased on analytical data from the published studies that describe the change inBlending E70 and Blending E100 values with the base gasoline’s E70 and E100 andwith ethanol contents in the range of 5 to 20% v/v. Vehicle Driveability Performance of Ethanol/Gasoline Blends Published studies on the impact of ethanol and gasoline volatility on vehicledriveability performance have also been evaluated. These included seven studieson Hot Weather Driveability (HWD) and eleven studies on Cold Weather Driveability(CWD). These studies show that modern vehicles are much less susceptible toHWD performance problems than are older vehicles. Some early model DirectInjection Spark Ignition vehicles tested by CONCAWE/GFC (2003) showed someHWD problems but only on high volatility fuels. Current specification propertiesappear to be adequate to control HWD but some increases in the E70 maximumlimits allowed by the European EN228 gasoline specification may be needed inorder to allow ethanol blending into gasoline at 10% v/v and higher. CWD vehicle performance is affected by mid-range gasoline volatility (E100) and isan issue for modern vehicles because it is linked to exhaust emissions performanceunder cold starting conditions. CWD is degraded by the use of ethanol/gasolineblends at the same volatility level as hydrocarbon-only gasolines. To reduce theimpact of ethanol, new Driveability Indices (DI) have been developed and applied insome extensive US studies. These DIs generally include ethanol offset terms inorder to control the impact of volatility on CWD performance. Although current E100volatility class limits are fixed in the European EN288 gasoline specification, thepublished literature indicates that the minimum E100 limits should ideally vary withambient temperature and should include an ethanol offset term in order to controlCWD performance. Based on these results, a European DI including an ethanoloffset term should be considered in order to account for the performance ofEuropean vehicles under European climatic conditions.