According to a recent study by Gladstein, Neandross & Associates (GMA), renewable diesel (RD) is playing an active part in ensuring that heavy-duty vehicles, including Class 8 trucks, are meeting near-zero emissions mandates in California. The study, which was prepared for the Bay Area Air Quality Management District (BAAQMD) and South Coast Air Quality Management District (SCAQMD), reports that RD “achieves a volume-weighted carbon intensity rating that is about 66 percent lower than petroleum diesel.” Currently, California’s transportation-related RD consumption exceeds a quarter of a billion gallons per year.

There are a number of specific advantages related to RD usage, according to the GNA report. The fuel can be produced from numerous renewable, low-carbon-intensity feedstocks while still using existing oil refinery capacity. This lowers infrastructure costs since there is no need to build new production facilities. Since it is similar to diesel both physically and chemically, RD can be used in existing diesel-powered trucks. This also lowers costs for fleets, since they do not need to alter vehicles or purchase new ones.

RD’s high cetane number and other qualities help to reduce engine-out NOx and particulate matter emissions by an average of 13% and 29%, respectively, with little or no visible changes to vehicle performance or fuel efficiency. According to some fleet managers It also improves performance and reduces life-cycle costs of diesel particulate filters (DPF).

The study recommends that trials be conducted to see how RD can improve both high-horsepower off-road and certain on-road applications, which could include both marine vessels and locomotives. The authors also recommended that the BAAQMD, as well as the California Air Resources Board (CARB), work with the Port of Oakland drayage truck fleet to perform a controlled test of RD usage within its fleet. This would help gauge whether or not switching to RD will improve DPF performance and durability.

GNA also suggested that CARB continue to work with air quality districts, heavy-duty engine manufacturers, and RD producers and suppliers to perform emissions testing to measure how RD affects engines with advanced emissions controls. Finally, the study recommended an assessment of the state’s supply and demand of RD. Both CARB and the California Energy Commission could act as ambassadors to promote a study on the future’s “supply and demand dynamics for RD as a major transportation fuel in California.”

Contributors to the study included the California Energy Commission; Neste US, Inc.; University of California, Riverside; CARB; the City of San Francisco; the City of Oakland; Cummins Engine Company; and AltAir Fuels.