A Shortcut in Engine Design: Specialized Software Models Soot Formation
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 test various engine designs virtually—saving both time and money in the effort to develop cleaner-burning engines in advance of pending regulations.
“More accurate simulation software allows more innovation because you can do more ‘What if?’ type of studies,” says Ellen Meeks, Reaction Design’s vice president of product development. “You can explore design concepts before you ever have an engine to build. The virtual prototyping lets you come to an optimal solution.”
Designing a new engine can typically take three to five years, Meeks says. Each design test cycle can cost $100,000 to $150,000 and can take as long as a year to complete.
Reaction Design CEO Bernie Rosenthal says the San Diego company, which has about 30 employees, formed the Model Fuels Consortium about six years ago to help develop the modeling software and put it to use. The consortium, which includes engine developers and fuel chemists from about 20 companies around the world, convened a two-day meeting in downtown San Diego this week to review the simulation program and discuss other technical advances.
“Automakers face a number of compliance issues like CAFÉ and Euro5+ that add to the complexity of engine design and lengthen the design process,” says Charles Westbrook, the consortium’s chief technical advisor and a senior scientist at the Lawrence Livermore Laboratory. In a statement from the company, Westbrook says members of the consortium recognized the importance of science-based soot modeling, which “can shave days, weeks, or months from a design cycle to get cleaner cars more quickly on the road.”
While Reaction Design organized the development effort, consortium members set the priorities and helped to validate the accuracy of the modeling program at various stages of development. As I explained a couple of years ago, the company specializes in software that models the gaseous chemical reactions taking place in turbines and combustion engines. But it wasn’t possible to build on existing software programs, and the latest project was developed from scratch, Meeks says.
The software simulates a process that occurs in milliseconds, and which depends on such variables as engine temperature, fuel-to-air mixture, environmental conditions, and type of fuel.
The fine black particulates known as soot consist mostly of carbon, and are formed when fuels don’t fully burn. The big leap that everybody wanted, Meeks says, was a program that could take all the chemicals and chemistry going into the moment of combustion—she calls them “soot precursors”—and accurately predict soot particle size and distribution based on the turbulent processes within the combustion cylinder.
Reaction Design says it will make the modeling program available to consortium members, which includes ConocoPhillips, GE Energy, PSA Peugeot Citroen, Oak Ridge National Laboratory, Toyota, and Volkswagen. Interested non-member companies can get exclusive access to the simulation software and other data by joining the consortium.