Two Colorado State University (CSU) researchers have received a $325,000 National Science Foundation grant to determine the pollutant formation chemistry of algae-derived biofuels, which have potential to be high-yield, efficiently produced, renewable fuels.

In the combustion of biodiesel and straight vegetable oil (SVO), the formation of pollutants such as NOx and soot has been linked to the chemical structure of the triglycerides present in the feedstock. Work is needed to characterize the combustion chemistry and pollutant formation chemistry of algae-derived biodiesel and SVO, which have far different fatty-acid compositions than typical vegetable or animal-fat feedstocks. The study will focus on homogeneous-compression ignition and partially premixed droplet ignition of algae-derived SVO, fatty acid methyl esters (FAME, i.e., biodiesel) and renewable diesel.

One of the reasons we’re interested in algae-based biofuels is because of their potential to reduce greenhouse gas emissions and to reduce our dependence on imported oil. What are the consequences if we were to suddenly go from zero to 20 billion gallons of algae-based biofuel per year over the next 20 years? Are there going to be any consequences that we may not have thought about? Recent history is littered with examples where we’ve moved too quickly with the technology without understanding the risks. Now is a good time to evaluate pollutant formation from these fuels—before they are in widespread use.

—Anthony Marchese

Marchese and Azer Yalin are working with Jeff Collett in CSU’s atmospheric chemistry department and John Volckens in environmental and radiological health sciences. Marchese’s research focuses on the fundamentals of how fuels burn and the particulate matter that is produced. Much of the work will be done at the CSU Engines and Energy Conversion Laboratory.

The researchers will perform combustion and pollutant formation studies using a rapid compression machine (RCM). An RCM is an instrument designed to simulate the compression stroke of a single engine cycle allowing auto-ignition phenomena to be studied in a much more controllable environment than that which is possible in an actual engine.

These experiments enable instantaneous measurement of gas-phase intermediates and pollutants such as NO, NO2, CO, CO2, formaldehyde, HCN and soot precursors, which can be compared against chemical kinetic models currently under development.

In other experiments, the ignition of a monodisperse liquid droplet stream in a high temperature oxidizing environment is being used as an analog to the heterogeneous diesel ignition and combustion process. This configuration allows quantitative, temporal and spatial measurements of NO, OH and CH in the vicinity of an igniting algae-based fuel droplet using planar laser-induced fluorescence (PLIF), along with soot volume-fraction measurements using laser-induced incandescence (LII).

They will then compare droplet data against a transient, spherically symmetric, chemically reacting flow model. Performing these combinations of experiments and modeling on algae-derived fuels will provide insight into both the rapid premixed-combustion phase, where prompt NOx and soot precursors are formed, and the transition to non-premixed combustion, where thermal NOx and soot are formed.

There is a lack of understanding of the chemistry behind NOx and soot formation from biodiesel in general. Algae-based biodiesel is unique and has a different chemical structure than feedstocks like soybeans, so we’re building several experiments to focus on the NOx production and soot as well. In diesel engines, NOx and soot are still a major concern.

—Azer Yalin