The aims were ambitious, with not all questions answered. A side project to evaluate the effects of biofuel exhaust particulates on the lining of lung tissue raised new questions about the atmosphere’s effects on the exhaust. However, the central goal, to determine whether the biofuel burned cleaner emissions than commercial diesel reaped interesting results.
Recipe for a biofuel experiment
Pollutants were measured at four different engine speeds (700, 1,000, 1,300, 1,600 rpm) and included greenhouse gases (CO2, carbon monoxide, and nitrogen oxides) and black carbon aerosols (small particles like smoke and larger particles like soot). Ultimately, the Sproul traversed more than 14,000 miles and burned through 52,000 gallons of biofuel. That’s a lot of data to make sense of.
The Sproul study was unique in using a hydrogenated biofuel, a new process that is supposed to increase shelf life and allow the engine to run cooler than that of other tested biofuels processed differently. This study was also the first to measure emissions collected across an extended number of miles because when our day cruise was over, the equipment stayed aboard to independently collect data over a year of the Sproul’s travels.
Does biofuel burn cleaner?
Back in the lab, Russell and her team crunched the numbers and determined the following: At lower speeds, the biofuel burned significantly cleaner in terms of greenhouse gas pollution (particularly CO2) but produced about the same amount of smoke and more soot than diesel. At higher speeds, the biofuel and diesel were comparable for greenhouse gas emissions, but the biofuel burned more smoke and soot overall than diesel. Both the biofuel and diesel affected lung tissue lining similarly, but these results were inconclusive because of the limited number of samples and the variability of atmospheric conditions. Finally, as advertised, the Sproul’s engine ran cooler and more efficiently with hydrogenated biofuel. What do we make of all this?
Before crowning the environmental winner, it is essential to consider not just emissions but the energy required to source and process each fuel type. Biofuel comes from living matter (easily grown and located above the ground), while diesel comes from petroleum, which must be extracted from deep in the earth via complicated, invasive practices (drilling, fracking). Because biofuels are easier and cheaper to access, process, and refine, they are more energy efficient from the get-go. And while not fully carbon neutral, the Sproul’s biofuel was 50 percent renewable, whereas diesel is considered zero percent renewable since it takes millions of years to form, and known viable reserves are bein depleted much faster than new ones are forming. Consequently, even though biofuel did not emit fewer emissions than diesel in every instance, it is still the ecological winner, especially for CO2.
Time for a smog check
Biofuel emissions from land vehicles have been investigated and improved on for more than 20 years, but only recently have biofuel’s effects on ocean-going vessels have begun to be studied. And unlike for our vehicles, emission restrictions on ships have not included carbon emissions. When you consider that the biggest ships (the cargo kind) burn through 100,000 gallons of fuel daily, that’s a Yeti-sized carbon footprint.
Looking into the future, international trade over the high seas is expected to increase, which translates to a larger chunk of total human-produced air pollution belching from the global shipping fleet. As cars become ever more energy efficient, ships could overtake them as the biggest polluters in some places. True, the proverbial ship has sailed in regards to climate change, but there is no reason to jump overboard.
Ship owners will be more agreeable to cleaner, renewable fuels if we support the science that innovates ways to make biofuels more cost-effective, particularly as fossil fuels get more expensive. And our planet wins as we pursue ways to increase the renewable fraction of biofuels and reduce greenhouse gas and particle emissions.
To reach these next milestones, we need more sampling to understand biofuel’s effects on human health. In the pursuit of cleaner fuels for ships, Russell said, “We should look at differences [in biofuel and diesel] between the Sproul and other ships, specifically different kinds and sizes of engines, particularly for the largest ships, which burn the most fuel of the worldwide fleet.”