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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.

This paper describes how the analytical methodology for fuels and exhaust gases was selected and developed for the experimental sectors of the EPEFE study. It covers the selection of standard test methods for fuels analysis and addresses how round-robin exercises in non-standard areas of fuels analysis were designed, organised, monitored and reviewed, and then used to define the approach to (and the scope of) the speciated fuel analyses. The paper also addresses how the exhaust gas analysis was designed in relation to emissions testing methodology. The means used to evaluate and, where necessary, optimise the exhaust gas speciation capabilities of participating laboratories, and in which round-robin activities were a key element, are also explained.

A review of cycle-by-cycle variations in combustion and early flame histories is used to discuss the origins of cyclic variations in spark ignition engines. The hypothesis that cyclic variations are caused by the displacement of the flame kernel, is tested by means of a phenomenological turbulent entrainment combustion model. The model results are compared with experimental cycle-by-cycle combustion data, from a range of operating conditions that covers changes in: fuel, air fuel mixture, ignition timing and throttle setting. The combustion is characterised by the cycle-by-cycle variations in: the indicated mean effective pressure, the maximum pressure, the maximum rate of pressure rise, the burn rate and the flame speed. The model predicts correctly the effect of changes in the engine operating point on the cycle-by-cycle variations in combustion, and in many cases there is also good numerical agreement.

A phenomenological model of turbulent combustion has been developed and validated against data from wide ranging tests on a Ricardo E6 engine. Most tests used iso-octane, with a range of air fuel ratios and ignition timings, for tests at full throttle (with and without knock) and at part throttle. Some full throttle tests were also conducted with methanol and toluene. The engine performance was characterised by mean and coefficient of variation (CoV) of: the peak pressure, the maximum rate of pressure rise, the i.m.e.p., the burn rate and flame speed measurements. The results have been used to argue that the cycle-by-cycle variations in combustion should be characterised by the CoV of i.m.e.p. in preference to the CoV of the maximum cylinder pressure. Evidence is also presented to support the observation that the cycle-by-cycle variations in combustion are lower when the early combustion is more rapid.

The effect of gasoline RVP on regulated exhaust emissions has been investigated in a fleet consisting of five current European vehicles. The effects of MTBE with changing RVP and E70 were also studied. All vehicles were equipped with the standard OEM small carbon canisters and three-way catalytic converters and the regulated emissions measured over the new European test cycle. A rigorous refuelling protocol was employed to ensure that the carbon canisters were loaded in a repeatable way before the emission tests. The results show that a reduction in RVP gave benefits in CO and NOx, but no effect on exhaust THC emissions. The benefits for CO and NOx were greater in non-oxygenated fuels. Of the five test vehicles, three showed CO emission benefits due to RVP reduction, whilst CO from the other two was insensitive to RVP changes. Four vehicles also showed NOx emission benefits due to RVP reduction whilst the NOx emissions from the other vehicle were insensitive to RVP changes.

A test programme has been conducted to study any potential long term effects of gasoline sulphur on catalyst performance, using a newly developed transient engine-bed ageing cycle. The ageing cycle, which was based on repeated European Extra Urban Drive Cycles, was chosen to ensure that the catalyst experienced a realistically wide range of temperatures and space velocities, together with transients, idle and periods of overrun. Two nominally identical platinum/rhodium catalysts (manufactured from the same batch) with matched lambda sensors, were aged for a period of 80,000 km each, one being aged using a gasoline containing 50 mg/kg (ppm wt) sulphur, the other being aged on the same fuel doped to 450 ppm wt S. The emissions performance of both catalysts was measured after 6,000, 40,000 and 80,000 km ageing, by fitting the catalysts to a test vehicle, and performing emissions tests over the European test cycle at both sulphur levels.

Engine-out emissions of unburnt hydrocarbons from spark ignition engines are attributable to a number of mechanisms, occurring during the engine cycle, by which fuel escapes combustion. These include absorption of fuel components into the bore lubricating oil film during compression, and subsequent desorption into hot combustion gases throughout expansion. A proportion of the hydrocarbons desorbed will then be emitted, either as unburnt or partially oxidised fuel. This mechanism has been studied by a number of workers, and estimates of its importance vary from 10 to 30% of total hydrocarbons being related to the absorption/desorption process. A novel lubricant additive has been formulated for the purpose of reducing the quantity of fuel which is absorbed into the bore lubricant film, and hence the quantity of fuel subsequently desorbed.

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.