Nucleation & Agglomeration 2

Trying to displace refined petroleum-sourced vehicle fuels with renewable alternatives is relatively straight forward, although there is some tinkering necessary to meet industry technical standards.

Jumping these hurdles could be seen as minor compared to measures that might be necessary to reduce the overall burden of air pollution from burning liquid biofuels and liquid Renewable Fuels in internal combustion engines (ICE).

Some emissions are suppressed or absent, for example, the levels of sulfur and sulfur compounds in the raw biomass products used to make biodiesel are significantly less than in fossil fuels. This should mean that the exhausts of burning biodiesel will cause less sulfate and less sulfur dioxide emissions to the atmosphere than burning fossil diesel.

There are hundreds research projects in this area. Since I’m not an expert in this field, I don’t know which research authors are best to reference, but I’m going pick a few at random, and work from there.

Let’s take, “Size distributions, PAHs and inorganic ions of exhaust particles from a heavy duty diesel engine using B20 biodiesel with different exhaust aftertreatments”, by Pi-qiang Tan, Yi-mei Zhong, Zhi-yuan Hu and Di-ming Lou, in Energy, Volume 141, 15 December 2017, Pages 898-906, DOI : https://doi.org/10.1016/j.energy.2017.09.122.

“Compared with the engine without exhaust aftertreatments, DOC [diesel oxidation catalyst] decreased nucleation mode particle number by 19.83%, while accumulation mode particles exhibited slight changes.”

So, to revise, “nucleation mode” refers to the process whereby individual atoms, ions or molecules group/stick/crystallise together to form a “nucleus”, the core of a particle; whilst “accumulation mode” refers to particles clumping together into “agglomerates”.

Tan et al. (2017) go on, “Compared with diesel fuel, many studies show that biodiesel can reduce particle mass, hydrocarbons (HCs), and carbon monoxide (CO) emissions, but nitrogen oxides (NOx) are slightly increased.”

Well, that seems like biodiesel offers several huge bonuses in curbing emissions; however, this is not across the board. The paper reads, “Tan et al. [2014] found that biodiesel fuel led to an increase in particle number concentration, especially small size particles, when compared with diesel fuel. Zhang [2011] drew the same conclusions. The particles, especially the small size ones, stay suspended in the atmosphere for a long time, and thus have a higher probability of being inhaled and consequently being deposited deep in the alveolar region of the human lung […] Nitrate, sulfate, and ammonium, in this order, presented the highest concentration levels, indicating that biodiesel may also be a significant source for these ions, especially nitrate. […] Biodiesel decreases the total PAH emission. However, it also increases the fraction of fine and ultrafine particles compared with diesel.”

So, biodiesel substitution for dinodiesel is not an unmitigated success.

And the situation changes with engine load. For a reference, I chose “Comparison of particle emissions from an engine operating on biodiesel and petroleum diesel”, by Jie Zhang, Kebin He, Xiaoyan Shi and Yu Zhao, in Fuel 90, 2011, 2089-2097, doi : 10.1016/j.fuel.2011.01.039 : they write, “The biodiesels were found to produce 19–37% less and 23–133% more PM 2.5 compared to the petroleum diesel at higher and lower engine loads respectively.” PM, of course, is particulate matter, and PM 2.5 is particulate matter of a diameter/size of 2.5 microns (micrometres, or millionths of a metre) or smaller.