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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.

In a collaborative programme, the effects of gasoline sulphur content on regulated emissions from three-way catalyst equipped vehicles have been studied. The programme evaluated the sulphur tolerance of three different catalyst formulations on the same range of vehicles. The catalyst chemistries were chosen to be representative of typical current formulations in different markets, as follows: 1. Platinum/Rhodium (Pt/Rh) 2. Platinum/Rhodium/Nickel (Pt/Rh/Ni) 3. Palladium/Rhodium (Pd/Rh) Each vehicle/catalyst combination was tested with fuels containing sulphur at nominal levels of 50, 250 and 450 ppm weight. All fuels were produced using the low sulphur fuel as a base and doping to 250 and 450 ppm S with a mixture of nine sulphur compounds, typical of those actually occurring in European gasolines. The results show clear differences between the magnitudes of the sulphur effect with different catalyst formulations.