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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.

Six full range gasolines were tested in two engines (one with a catalyst) operated at 4 steady states. Engine-out regulated emissions responded to equivalence ratio, Φ, in the accepted manner. For both CO and NOx, there was a characteristic, single emissions response to changes in Φ. Changing fuel composition will primarily alter the production of these emissions by modifying the stoichiometric air/fuel ratio, projecting engine operation onto another part of the Φ response curve. These Φ effects, which are independent of engine design, also determine how operating conditions affect engine-out CO and NOx. Speciated hydrocarbon measurements at engine-out and tail-pipe confirm results seen in previous test-cycle based programmes.

A “CARS” System using a modeless dye laser has been extensively calibrated and shown to give average temperatures of acceptably good accuracy. It has been used to measure temperatures in the end-gas of a single-cylinder E6 engine under knocking conditions using propane, commercial butane, iso-octane and a primary reference fuel made up of 90% iso-octane and 10% n-heptane by volume. These measurements show that there is significant heating of the end-gas because of pre-flame chemical reactions for all the fuels except propane. Propane has to be compressed to a much higher pressure compared to the other fuels studied in order to make it knock. At a given engine operating condition, there is significant cycle-by-cycle variation in both combustion and knock.

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.

Vehicle-based studies have shown that a reduction in the aromatic content of gasoline fuels can result in increased NOx emissions from catalyst-equipped vehicles. A study with simulated exhaust gas has shown that light paraffins, especially methane, are unreactive and cause substantial breakthrough of unreacted NO over the catalyst. However, unsaturated exhaust components including aromatics are effective reactants and play a large part in converting NO over the catalyst. Engine tests have shown that methane is predominantly produced by fuel paraffins and olefins, but hardly at all by aromatics. Thus it appears that methane generated during combustion of low aromatics fuels may be the cause, wholly or in part, of the poor NO conversion efficiency observed when catalyst-equipped cars are operated on such fuels. However, it cannot be excluded that low aromatics fuels are associated with increased air-to-fuel ratio which will also contribute to poor NO performance.

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.

Increasing interest in gasoline engine emissions has focused attention on the fuel compositional and emissions effects that govern NOx conversion over the catalyst. This study reports the transient effects of individual species emissions and catalyst conversions on NOx conversion made using Fourier Transform Infra Red (FTIR) spectroscopy of the engine-out and tailpipe emissions (regulated and speciated) during the testing of a catalyst equipped gasoline vehicle run on multi-component model fuels over the standard European cycle. FTIR measurements confirm that transient NO conversion is directly correlated with that of CH4, especially within the Urban Drive Cycle (EUDC). Other hydrocarbon species do not govern the transient variability in NO conversion. This vehicle maintained ϕ≤ 1.0 practically throughout the EUDC and consequently no correlation was seen between transient NO conversion and equivalence ratio.