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The effect of diesel fuel properties and composition on regulated emissions has been investigated in an IDI naturally aspirated passenger car equipped with an oxidation catalyst. The influence of diesel fuel changes on emissions from this same vehicle without the catalyst have been reported in a previous SAE paper (1).* The addition of the catalyst to this ‘clean’ car further reduced emissions, especially those of hydrocarbons and carbon monoxide. Particulate emissions were reduced to below the proposed 1996 European limit of 0.08 g/km. The catalyst was especially effective in reducing particulates from the higher density fuels, but had no influence on NOx. The catalyst was ‘sulphur tolerant’; changes in fuel sulphur content between 0.01 and 0.2% wt sulphur had a an insignificant effect on particulate emissions. Variations in fuel properties produced a significant influence on emissions, although the effect was less in this car, with a catalyst, than in the non-catalyst version.

Six European vehicles fitted with carbon canisters have been tested under severe conditions to establish if evaporative losses of volatile organic compounds occur under European driving conditions - so-called “running losses”. The programme entailed the development of a point source measurement technique which has a number of advantages over other methods currently in use. Following the development and validation of the measurement technique, the six vehicles were tested at 28C over a range of driving cycles on a gasoline with a Reid vapour pressure of 90 kPa. None of the vehicles exhibited classical running losses, i.e. losses during higher-speed driving. This was due to the effectiveness of canister purging in these conditions. However, significant volatile organic compound (VOC) losses were observed for several vehicles during idle after a period of driving had heated the fuel. Substantial car-to-car variation was observed in the losses obtained.

The influence on regulated emissions of diesel fuel properties and composition has been investigated in an IDI passenger car fitted with EGR. The key findings were confirmed in limited tests on two other advanced technology European diesel passenger cars. This work is part of an on-going joint cooperative project involving Esso and Statoil. Tests on 37 fuels enabled the individual influence on emissions to be determined of fuel aromatics content, cetane quality, back end volatility (T95), density and sulphur content. This study reveals that the key fuel parameter influencing particulates in European diesel cars is density. In the typical European range of fuel densities (below 0.86 kg/l) there is a linear relationship between density and particulates. In this region T95 is also influential but increasing cetane number above 48 has negligible effect. Aromatics content is decisively shown to have no significant influence on particulates.

Evaporative emission levels have been determined in a CONCAWE* programme for a range of ten uncontrolled European vehicles using a modified SHED test procedure as developed by the CEC*. Three extra vehicles were tested which were equipped with evaporative and exhaust emission control systems, but of the same make and model as three of the uncontrolled test cars. The vehicles were tested using several warm-up cycles and on a range of fuels whose volatility parameters were independently varied, including oxygenate blends. Exhaust emissions were determined and a few measurements of true diurnal emissions carried out. Vehicle fuel system design had the greatest effect on evaporative emissions which varied between 4 to 16 g/test on a typical European summer fuel. Gasoline volatility had a significant but smaller effect and RVP was shown to be the dominant fuel parameter. At the same volatility, oxygenate blends gave similar or lower emissions than hydrocarbon fuels.

The spread of octane requirements due to tolerances in engine manufacture has been investigated to indicate the potential improvement in fuel economy which could be achieved by making better use of the available gasoline octane quality. The wide spread of octane requirements in the 48 cars studied resulted in “octane waste”, a measure of the inefficient use by engines of the available octane quality. The average waste was three octane numbers and is associated with variations in compression ratio. The wasted octane can be made available to improve fuel economy through tighter control of manufacturing tolerances on combustion chamber volumes.