In Fairbanks, AK (where I spent a year after I graduated from college), winter temperatures can plunge to minus 40 degrees (F) for weeks at a time, creating ideal conditions for a local phenomenon called “ice fog.”
When temperatures get that cold, the air can’t hold much water vapor. Automotive engine exhaust is mostly water vapor, so emissions go from a maximum cylinder temperature of, say, 3,100 degrees (F) to minus 40 in a matter of seconds. Vapor cooled that fast forms tiny ice particles so small that 10 could fit side-by-side on the edge of a piece of paper. They also are so light that they remain suspended in mid-air—and of course each one is coated with fine soot particles. In short, the ice fog that eddies and curls through the winter streets of Fairbanks is a surreal cloud of pale brown murkiness.
It might seem like a remote problem, but the sub-arctic temperatures in Fairbanks visually illustrate a process that happens much less visibly with internal combustion engines everywhere.
Over the past decade or so, air quality regulations have focused chiefly on limiting the overall amount of soot emitted by internal combustion engines, but recent studies indicate that soot particles smaller than 100 nanometers can be especially harmful to human health. As a result, new “Euro5+” environmental regulations set to take effect next year are intended to substantially reduce the size and number of soot particles emitted by gasoline and diesel-powered cars and light trucks throughout Europe.
Some industry observers say it’s only a matter of time before U.S. environmental regulators impose similar restrictions on fine soot emissions.
Still, reducing soot emissions represents an unusual challenge for engine makers, in part because the targeted soot particulates in engine exhaust are nano-sized flecks of nothingness. (For the sake of comparison, the thickness of a human hair ranges from 50,000 to 100,000 nanometers.) Current methods of engine design rely more or less on the empirical results of trial and error, which can be a costly and time-consuming process when it comes to building and testing a series of engine prototypes.
So it was a welcome breakthrough when San Diego-based Reaction Design said recently it had led a consortium in developing software that can accurately simulate the formation of soot particulates during internal combustion. Engine designers can use the modeling software to
