Diesel sulfur content impacts on Euro VI soot-free vehicles: Considerations for emerging markets

Euro VI diesel engines contribute significantly to vehicle emission reductions because they have advanced emission control aftertreatment systems for particulate matter (PM) and nitrogen oxides (NOx). These systems are sensitive to the sulfur content in diesel fuel, and for this reason, most major vehicle markets have progressively limited fuel sulfur content to 10 parts per million (ppm), also known as ultralow-sulfur diesel. As emerging market nations adopt soot-free Euro VI emission standards for their new vehicles, they face a transition to ultralow-sulfur diesel, as well. But this fuel quality transition does not happen overnight. In some cases, Euro VI vehicles are fueled with higher sulfur content fuels during a nationwide transition, or due to regional fuel quality differences. Through a review of recent literature, this paper explores the impact of 50 ppm sulfur fuels on Euro VI technologies. We find that, while all emission control systems achieve maximum effectiveness around 10 ppm sulfur or less, some temporary exceedance of these levels can be tolerated without adverse effects. After short-term exposure to sulfur content at 50 ppm, adverse effects on emissions performance can be reversed with increases in exhaust gas temperatures. However, long-term exposure to 50 ppm sulfur introduces more serious challenges for real-world emissions compliance, including impaired diesel oxidation catalyst (DOC) operation that leads to thermal degradation of diesel particulate filter (DPF) and selective catalytic reduction (SCR) systems, and direct poisoning of catalyst sites on DPFs and zeolite-SCRs. Given this, governments wishing to achieve soot-free Euro VI real-world emission control performance should accelerate the fuel transition and limit nationwide diesel fuel sulfur content to 10 ppm.