As five Midwestern states add soot alerts to their warning system for dirty air, one University of Missouri-Rolla researcher is trying to get to the root of the soot problem.
For the past five years Dr. Umit Koylu, an associate professor of mechanical and aerospace engineering at UMR, has been investigating how the microscopic particles form during combustion.
"Whenever you burn any kind of hydrocarbon fuel, especially coal, you release solid particles into the atmosphere," Koylu explains. "These very small, nanometer-sized particles are inhaled and studies show they are not good for our health or our environment."
The Environmental Protection Agency has set emissions standards for coarse particles — those larger than 2.5 micrometers or 1/20th the width of a human hair — but not for smaller particles.
"It turns out that all the combustion particles are less than 2.5 micrometers," Koylu says. "When you look at these particles under a microscope, you see the individual particles are always about the same size, between 15 and 50 nanometers or about 20 times smaller than the EPA limits. These individual particles collide with each other to form grape-like clusters, but even the overall size of these irregularly shaped aggregates is typically under one micrometer."
While it may seem like larger individual particles would be more dangerous, Koylu says these clusters of tiny particles pose a bigger problem because of the increased surface area.
"When these particles are deposited on our lungs or when they interact in the atmosphere with other gases or emissions, surface area is everything," Koylu explains. "If the surface area is more, it absorbs more of the human tissue. You can see why the overall size of the clusters is not really the most relevant parameter."
Koylu and his students, using funds from a CAREER grant from the National Science Foundation, have developed techniques to describe the types of solid particles found in turbulent flames. The CAREER program supports the early career development of teacher-scholars who are to become academic leaders.
One method involves shining a laser into a soot-containing flame to see how the laser interacts with the particles. "By looking at how much the particles scatter and how much they absorb the light, we try to obtain all the physical parameters without disturbing the flame," Koylu says. "It’s a detective game, similar to an investigator trying to figure out the weight or height of a person who left footprints at a crime scene."
Using electromagnetic theory, the research team came up with ways to describe the particles, including the diameter of individual particles, overall size of clusters, concentration and morphology or structure.
In addition to laser diagnostics, the team needed to collect and measure actual soot particles. But using sampling techniques are difficult, Koylu explains, because the microscopic particles are formed in a matter of milliseconds. Plus anytime a probe is placed into a flame, it’s possible to disturb the environment.
"The best way to describe our probe is that it’s like a frog’s tongue," Koylu says. "It goes into the flame, collects, and removes of sample of particles on the probe in a matter of milliseconds. The probe is cold and the particles are hot. If you’ve watched ‘A Christmas Story’ where the kid puts his tongue onto a pole and couldn’t take it off, you’ve seen the same force at work. Particles are driven onto the probe."
The research team’s ultimate object is to control the formation of the soot particles. "If we can control how they are being formed in a flame, we can control how they are being emitted from any kind of internal combustion engine and reduce the effect of these particles on the environment and our health," Koylu adds.
Economics is another driving force behind Koylu’s work. "Environmental and health problems cost a lot of money, but at the same time, efficiency is compromised when these particles form," Koylu adds. "When they form, thermal efficiency goes down and they also collect onto the combuster walls. These particles deposit on turbine blades, which are simply metal surfaces, and reduce durability. All these technological, environmental, and health-related issues also have economic implications."