Impact of lubricating oil on particulates formed during combustion of diesel fuel—a shock tube study

The advent of more stringent standards to reduce particulate emissions has increased the need to control the contribution that consumption of lubricating oil in engines makes toward particle emissions. Although many studies have been done in this area, the main mechanism by which lubricating oil contributes to particle formation is not well understood. In this study, the impact of lubricating oil on particle emissions from diesel fuel combustion was investigated. Combustion of D-2 diesel fuel with two concentrations of Pennzoil 10W40 motor oil (0.5 and 2 wt%) was studied over a temperature range of 1200–2300 °C at pressures of 5, 14 and 24 atm. All experiments were conducted in a modified single pulse reflected shock tube. The fuel and lubricating oil mixtures were injected using a high pressure fuel injector. The addition of lubricating oil led to higher particulate yields at higher combustion pressures. The increase was more evident with higher lubricating oil concentrations. However, at lower pressures, neither concentrations of lubricating oil had any impact on particulate yield. The results agree with previous studies where an increase in particulate yield was observed with an increase in lubricating oil consumption and pressure. The results observed confirm the hypothesis that lubricating oil present in the combustion chamber during the combustion process could contribute to particle emissions.