Predicting more accurately what happens in the complex chemical reactions between air and fuel when they are compressed and ignited in an IC engine’s combustion chamber—and solving the challenge of exhaust particulates—may have taken a step forward with the creation of the Computational Chemistry Consortium (C3), driven by the auto industry’s need to meet increasingly stringent global emissions regulations.
“Several of our existing clients asked if we could develop an open format fuel consortium that wasn’t tied to any particular software and would allow them to run it in conjunction with their own programs, a bit like an open source format,” explained Eric Pomraning, Ph.D., Vice President of Convergent Science, Inc., a maker of computational fluid dynamics (CFD) analysis toolsets based in Madison, WI. Its Converge numerical tool is used for combustion chamber simulations.
Customer demand led Dr. Pomraning’s company to organize and co-sponsor an event, the 2016 Combustion Summit, which included technical presentations by research experts from FEV, Aachen University, IFPN Energies Nouvelle, Volvo Cars, Brandenburg University of Technology (BTU Cottbus), Renault, PSA Peugeot Citroën and the NUI Galway. Automotive Engineering attended the two-day conference in Nice, France, and spoke with a number of presenters and attendees.
Although there have been previous attempts to model combustion these tend to have tied users to specific software sets. Among the advantages of running an open platform, claimed Kelly Senecal, Convergent Science’s Vice President and co-founder, are no restrictions on what tools you can use it in, he noted, which benefits the user community at large.
Convergent Science is encouraging fuel companies such as Saudi Aramco, as well as OEMs and consultancies, to partner in the new consortium while allaying any fears that competitive advantages in either fuel formulations or engine designs will potentially leak to rivals.
“We’ll build up base mechanisms and if they [oil companies] feel they have an additive or something that really improves the combustion, knock resistance, emissions, they can add that to the mechanism on their own away from the rest of the consortium,” explained Dr. Pomraning, who was a research associate at the University of Wisconsin-Madison Engine Research Center prior to co-founding Convergent Science.
He said the combustion-research community is looking for “a good mechanism to predict emissions and soot because the chemistry is so complex.” The same rings true for the OEMs, consultancies or Tier Ones: “Anything proprietary like piston bowl design, for example, won’t be part of this [consortium],” added Senecal.
Meeting the soot challenge
Exhaust particulates, or soot, are a significant technical challenge for the industry as well as an ongoing public health issue. Although some of the latest simulation models are capable of predicting particulate size and distribution, Senecal warned that “You have to get the chemistry right before you even worry about that, as that’s what kicks off the soot formation – that will be a big part of C3 understanding the chemistry to start the prediction of soot.”
“Maybe we have to develop some new CFD models for this,” offered Clément Dumand, Manager-Modeling of Energetic and Combustion Systems, Advanced Engineering and Research at PSA. He said the industry needs “more detailed combustion simulation for HC [hydrocarbons], soot and knock and I think maybe large eddy simulation (LES) might be the answer to this.”
Dumand was quickly joined by other speakers bemoaning the lack of adequate CFD software and meshing capability capable of accurately predicting the amount of soot a gasoline or diesel ICE will emit. “It’s very important for us to check that we have a system which prevents generation of too-small particles [so] we comply with the European requirements for particulate size and numbers,” explained Fréderic Ravet, a combustion systems expert at Renault.
Added Mattias Ljungqvist, a combustion simulations engineer at Volvo Cars: “Soot modelling is an issue. Even if NOx is supposed to be easier to handle we don’t always get the benefits that we see in simulations.”
“Soot is like the house of cards that’s built on everything else,” observed Kelly Senecal. “You have to get the flow reasonably right, the turbulence, combustion, spray and part of why soot is so challenging is because it’s at the end of everything. Compared to other things it’s also at very small levels so being able to predict a value at that kind of detail is very difficult.”
And the physics of soot are not fully understood. “We have a general idea of how it works, but we haven’t got it entirely figured out,” Senecal said. “The other thing is we model soot as another gaseous species, so there’s an issue right now in that we don’t model the right phase. We’re starting to work on that with some other collaborations modelling those particles, the solid particles mix and the load numbers, but it’s not easy.”
In the complex chemistry that’s involved in building up soot, the formation of polyaromatric hydrocarbons (PAH) is critical—and getting that chemistry right is a challenge, according to the experts. Scientist Dr. Fabian Mauss of BTU Cottbus is working on mechanisms that involve numerous species involving lots of reactions that are expensive to solve. Experts at the Combustion Summit noted that their teams are investigating what short cuts are possible and what assumptions can be made to get solutions.
Senecal said some of his company’s latest models are capable of predicting particle size and distribution. Getting the chemistry “right” first is vital because it’s what “kicks off” the soot formation. That’s a major goal of the C3 project. The consortium is actively seeking partners for the project which Senecal predicts will last for least three years with a renewal option. Interested organizations can contact company leadership through the website: https://convergecfd.com/.