Effect of Fuel Ethanol Content on Exhaust Emissions of a Flexible Fuel Vehicle

The European Union is aiming at increasing the market share of biofuels in order to improve the security ofsupply of transport fuel and to reduce CO2 emissions. The target is to reach a 10% of fuels from renewablesources on energy basis in the transport sector by 2020 and biofuels represent one of the most importantoptions. Bioethanol and biodiesel represent the only biofuels currently available on the market in big quantitiesand technologically mature. Bioethanol is probably the most broadly employed alternative fuel in the world(mainly in Brazil, USA and Sweden). An experimental program was carried out at the JRC to investigate the emissions of a flexible fuel vehicle usingdifferent ethanol/gasoline blends. In this report we will focus on the effect of fuel ethanol content on exhaustemissions from a Flexible Fuel vehicle and on some issues related to the use of bioethanol as transport fuel. The test vehicle was a passenger car currently marketed in Europe and one of the most popular modelsbelonging to the flexible fuel vehicle category. Emission tests were carried out both following the Europeancertification procedure (NEDC cycle) and using a US driving cycle (US 06). Regulated and unregulatedemissions were measured. Three different fuels have been tested: a standard commercial summer gasoline marketed in Italy used as basefuel and two gasoline/ethanol blends, which have been obtained by splash blending ethanol in the standardgasoline. The two gasoline/ethanol blends contained respectively 10% ethanol (E10) and 85% ethanol (E85). In general the repeatability of emission measurements was not very good; only with E85 the measured emissionlevels were very repeatable. The poor repeatability might be linked to the very sophisticated enginemanagement system which modifies the engine settings depending on the ethanol content of the fuel.Nevertheless sound conclusions can be drawn for the NEDC cycle while for the US 06 this is more difficult dueto the limited number of tests performed. The results have shown that over the European NEDC cycle the vehicle complies with the Euro 4 emissionstandards with all the fuel with the only exception of CO with fuel E10. In some cases the CO value measuredwith fuel E10 resulted to be slightly higher than the limit (1 g/km). CO and HC emissions measured over theNEDC cycle with fuel E10 resulted to be higher than with the other two fuels. On the contrary, E85 was the leastemitting fuel as far as these emissions are concerned. The influence of fuel composition was instead almostnegligible for NOx emissions. A statically significant increase of NOx emissions was noticed only in the case ofE85 and only over the extra-urban part of the NEDC cycle. CO2 emissions were reduced by about 4-6% withfuel E85 both over the NEDC and over the US06 cycle. Similar trends have been found in a recent, major Canadian study, with the only exception that CO emissionswere slightly reduced with E10 – a finding that may be explained by the different test cycles. While particulateemissions measured over the NEDC cycle were very low, the PM levels turned out to be quite high over the US06 cycle. In this case the emissions were comparable to those of a Euro 3 diesel car. This might be due to thevery aggressive driving pattern of the US 06 cycle which contains very hard accelerations. In these conditionsthe engine is likely to work in open loop and with a very rich mixture. The most significant effect of ethanol in thefuel was observed for emissions of carbonylic compounds. This effect increased with increasing ethanolconcentration. In particular for acetaldehyde E85 resulted in a more than twenty fold increase in emissions. Thisrepresents the main concern associated with the use of flexible fuel vehicles. Comparably with HC emissions,from the speciation of VOCs emissions the fuel E10 resulted to be the most emitting fuel while E85 the leastemitting one. E85 resulted in a reduction of 57% of the sum of the speciated VOCs compared to standardgasoline, but with an enrichment of C2 compounds. Emissions of toxic compounds such as benzene and 1,3-butadiene also decreased when E85 was used instead of standard gasoline. Contributions from ethene andpropene prevailed regarding the potential of ozone formation.