The impact of lubricant sulphur and phosphorus levels on the formation of nucleation mode particles was explored in a light duty diesel vehicle operating over the New European Drive Cycle (NEDC). All measurements were undertaken using a Scanning Mobility Particle Sizer (SMPS), sampling from a conventional Constant Volume Sampler (CVS) system. Rigorous sampling system and vehicle conditioning procedures were applied to eliminate oil carry-over and nanoparticle artifact formation.
An initial vehicle selection process was undertaken on vehicles representing three fuel injection strategies, namely; distributor pump, common rail and unit injector. The vehicles met Euro III specifications and were all equipped with oxidation catalysts. Idle and low load stability were key requirements, since these conditions are the most significant in terms of their propensity to generate nucleation mode particles.
The influence of fuel sulphur on nucleation particle generation is well documented and three fuels were tested at idle to confirm the chosen vehicle's response to fuel sulphur. Traditional European fuels exhibited strong nucleation modes, with the 50ppm S fuel showing ∼12% greater nucleation mode levels than the 10ppm S fuel. Swedish Class 1 Diesel (SWCL1) fuel gave a very stable nucleation particle mode, but at a lower level. This fuel was selected for the lubricant effect study since it was believed that its reduced final boiling point would not overlap with or interfere with the oil discrimination phase of the work.
A total of 9 oils were tested with sulphur and phosphorus levels ranging from 0 to 0.9 and 0 to 0.1%wt respectively. All the oils were fully formulated having SAE “X”W-30 viscosities and a targeted ACEA A5/B5 performance level. Test order was carried out under strict statistical control.
Oil derived sulphur and phosphorus were both found to increase the production of nucleation mode particles. Little effect of lubricant formulation on accumulation mode particles was observed. Swedish Class 1 (SWCL1) Diesel fuel provided substantial reductions in nucleation mode particles.