The impact of fuel hydrotreatment on Diesel exhaust emissions is investigated.
Several fuels are formulated in a refining pilot unit. By progressively increasing the hydrotreatment severity, sulfur reduction is first achieved, followed by aromatic reduction and cetane enhancement. The operating conditions and the effect on fuel characteristics are detailed.
The influence of this hydrotreatment on exhaust emissions of a light-duty prechamber engine is studied under both steady-state and transient conditions. In steady-state operation, a slight effect of fuel on CO and HC emissions appears which increases when the injection timing is retarded. No evidence of fuel influence on particulate emissions is found except for a sharp increase due to sulfate contribution for fuels with high sulfur content.
The transient operation enhances the influence of fuel characteristics on pollutants. The high interdependence of fuel properties within the fuel matrix makes it impossible to determine the separate effect of a single parameter. However, it is clearly shown that CO, HC and particulate emissions, measured on European standard cycles, are well correlated to any fuel characteristic directly linked to the hydrotreatment severity (aromatic content or cetane number).
This study shows that for an engine presenting low emissions level and for fuels with cetane higher than 50, the effect of fuel quality on pollutants is not pronounced. Nevertheless, it is shown that in the most severe conditions like urban cycle with cold start or operation at retarded timing, the hydrotreatment of diesel fuel by decreasing the aromatic content and raising the cetane number helps to reduce the pollutant emissions of a light-duty diesel engine.