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The effects of fuel formulation changes on vehicles meeting European Stage 1 (91/441/EEC) and Stage II (94/12/EC) emission limits have been investigated. Vehicles in the Euro Stage II fleet were advanced specification versions of the vehicle models in the Euro Stage I fleet. However, the basic engine blocks and capacity were the same. The observed improvements in emissions were attributed to changes, such as position of the catalyst and lambda sensor, improved fuel delivery systems, and to improvements in engine control strategy. These engine modifications resulted in reduced catalyst light-off times and improved AFR control. Emissions improvements, over the modified European test cycle, as a result of these changes were approximately 50% for CO and NOx and 30% for THC. A fuel matrix was designed in order to study the effect of six fuel parameters on exhaust emissions from the two levels of vehicle technology.

A set of designed fuels was tested in two European gasoline vehicles driven over the standard European Drive Cycle. Both regulated and speciated emissions were measured, together with HC, CO and NOx, pre- and post-catalyst. The main fuel set was a 3 by 3 matrix, where mid-range volatility (T50) and aromatics were independently varied from 85°C to 115°C for T50 and from 25% vol. to 45% vol. for aromatics. Two further fuels, together with the centre point fuel from the main matrix, formed a back-end volatility (T90) subset experiment. The fuels were blended from mixtures of pure chemicals in order that the chemical and physical properties could be closely controlled and kept independent. The findings of this two car trial are generally in line with the recent EPEFE programme and confirm that fuel changes which reduce one type of emissions (HC and CO) generally increase another (NOx) and vice versa.