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Scripps research ship fueled by 100% NEXBTL renewable diesel for 1 year; emissions analysis

In 2014, Scripps Institution of Oceanography received a grant from the US Department of Transportation to test the use of biofuel on the research vessel Robert Gordon Sproul for more than a year. Spearheaded by Scripps Associate Director Bruce Appelgate and co-led by Scripps atmospheric scientist Lynn Russell, the biofuel project investigated the viability of using hydrotreated renewable diesel fuel (HRD) on a long-term basis.

The Scripps researchers originally wanted to test renewable biodiesel produced from algae, but no manufacturers made algal biodiesel in the volume needed. Appelgate was able to take advantage of a newly-established reliable supply chain for another type of biodiesel, a hydrogenation-derived renewable diesel (HDRD) —purchased from Neste Oil Corporation: NEXBTL Renewable Diesel.

The 125'R/V Robert Gordon Sproul is powered by two Detroit Diesel 12V-149 (12 cylinders, V-shape), 675 hp main engines, with a White-Gill trainable hydraulically operated 155 hp bow thruster and two 75 kW generators. Fuel consumption is 1,350 gal/day at full speed, 850 gal/day average. Click to enlarge.

The drop-in HDRD used to power R/V Robert Gordon Sproul did not require any engine adjustments adjustments. Over the course of the biofuel experiment, which began in September 2014 and ran through December 2015, R/V Robert Gordon Sproul conducted 39 regular oceanographic research and education missions, spanning 89 operational days at sea, covering more than 14,400 nautical miles, and involving 527 scientists and students.

In the process, the vessel used a total of 52,500 gallons of 100% renewable diesel. All the while, Russell and her team used instruments installed on board to continuously measure pollutants such as carbon monoxide (CO) and nitrogen oxides (NOx), organic and black carbon aerosols, and engine performance to characterize differences between conventional and renewable fuels.

During two separate five-day research cruises aboard the ship, Scripps postdoctoral scholars Raghu Betha and Derek Price—both with the Climate, Atmospheric Science and Physical Oceanography (CASPO) division at Scripps—collected data for studies that focused on the air quality-related emissions from biofuel in comparison to the emissions from ultra-low sulfur diesel.

Two separate tanks on R/V Robert Gordon Sproul held biofuel and diesel, and the researchers could run the ship’s engine from either source, switching back and forth as needed to collect different emission samples.

Betha’s research focused mainly on the direct emissions coming from the ship’s stack (the exhaust piping at the top of the ship) and the criteria of pollutants for air quality. An inlet from the ship stack led directly to an air-sampling trailer, which housed instruments to measure the emitted particles and gases such as CO2 and NOx.

He found that the amount of NOx emissions were about 13% lower for biofuel, especially when the ship was running at lower speeds (700 and 1,000 revolutions per minute). The particle emissions, however, were 35%t higher for biofuel, especially when the engine was running at higher speeds (1,600 revolutions per minute). Black carbon or soot counts were also slightly higher for biofuel.

Betha believes that the benefit of having a decrease in CO2 emissions could outweigh the negative of higher particle emissions, since CO2 is a bigger problem for climate. Further, the decrease in NOx was a welcome surprise, since many other types of biofuel have shown increased NOx emissions, said Betha.

Price’s research focused on looking at the organic chemistry of the particles from the two different fuel emissions, and he also looked at what happens after the emissions have aged in the atmosphere.

He was able to track emission particles after their release into the atmosphere by “chasing them,” a feat that required a team effort. The scientists would release a track or “plume” of emissions, and then the captain would look at the wind patterns and turn the boat around to follow the plume, allowing Price to measure how the particles changed or “aged” over the span of a few hours.

The plumes, which are not visible to the naked eye, could be detected with instruments that were designed by the Atmospheric Aerosol Group, Russell’s lab at Scripps. Crewmembers also helped monitor the live particle counts, and alerted the captain if the ship was drifting out of plume range.

Price found that the emissions from both biofuel and diesel plumes were actually quite similar and mostly composed of long carbon chains of alkanes. These large alkane hydrocarbons were then oxidized, changing into more oxygenated compounds due to aging (photochemical reactions) in the atmosphere.

He and the other scientists also found evidence of sunlight breaking apart the molecules in both the fuel types. The researchers think that both types of fuels produce both gases and particles, and then sunlight breaks up some of the vapor molecules and that causes them to make more particles.

Both Betha’s and Price’s study results have been submitted to the journal Aerosol Science and Technology. The entire research team is hopeful that the proven success of biofuel to run an academic research ship will facilitate future use of renewable fuels on Scripps and other research vessels.

R/V Robert Gordon Sproul is once again running on diesel as its biofuel supply ran out in December 2015. The biofuel costs about 10% more than fossil fuel.


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