Climate and Emissions Benefits of Renewable Diesel: In-Use Testing of a Tier 2 Commercial Harbor Craft

Renewable diesel (RD or R100) is a leading non-petroleum fuel that has a lower carbon intensity than, and can be used in place of, petroleum-derived ultra-low sulfur diesel (ULSD or conventional diesel). Emissions of oxides of nitrogen (NOx) and particulate matter (PM) from engines fueled with RD compared to engines fueled with conventional diesel have been shown to decrease on the order of 10% and 30%, respectively, across multiple categories of on- and off-road heavy-duty diesel engines that do not use after-treatment such as selective catalytic reduction (SCR) or diesel particulate filters (DPF). However, the emissions benefits of RD have never been directly demonstrated in category 1 marine-certified engines used in commercial harbor craft (CHC) applications. In this study, portable emissions measurement systems (PEMS) were used to test and it was found that RD, in comparison to conventional diesel, reduced NOx emissions by 11.8%, from 5.13 to 4.53 g/bhp-h, and PM emissions by 26.5%, from 0.130 to 0.095 g/bhp-h. This study confirms emission benefits of RD relative to conventional diesel also apply when RD is used in marine engines. Tailpipe CO₂ emissions for R100 were 6% lower using RD instead of ULSD, but this does not consider the more substantial lifecycle benefits (58%) of using renewable diesel. Although lifecycle climate benefits are achieved by displacing ULSD from any sector, strategically directing limited supplies of RD to marine and other off-road sectors that have less stringent emissions controls as compared to on-road mobile sources maximizes its NOx and PM emissions co-benefits.