|The second phase of MFC work will focus on modeling the formation of particulates—especially the ultra-small particles that are deposited in the alveoli of the lungs, rather than being snagged in the upper airways. Click to enlarge.
Reaction Design, the developer and distributor of CHEMKIN for the modeling of gas and surface-phase chemistry, will launch a second phase of the Model Fuel Consortium (MFC) focused on particulate emissions upon the completion of the first phase of MFC work in December.
The MFC is a collaboration of engine companies, energy companies and research laboratories, led by Reaction Design, which is developing model fuels to support the development of cleaner-burning, more efficient engines and fuels by enabling accurate simulation results.
Fuel properties affect a number of combustion and engine properties, including ignition delay; knocking tendency; flame speeds; pollutant emissions; sooting tendency and particle size distributions; and density, viscosity and heating value.
However, real fuels, with their hundreds of components, are too complex to simulate directly. The MFC uses one or two molecules to represent each significant chemical class (examples in table below), and builds detailed chemistry models for each molecule.
|Real Fuel Component
|Surrogate Fuel Candidate
|iso-octane, hepta-methyl nonane
|methyl stearate, methyl linoleate
Launched in 2005, the MFC to date has developed a new methodology for model fuel creation, and created a database of fuel component models. It has also proved the accuracy of the models through extensive validation. Currently, the MFC is working on adding bio-components, such as ethanol, to the database.
We’ve focused on five-component fuel models for diesel and gasoline. It’s an approximation, but an approximation based on fact.—Bernie Rosenethal, CEO Reaction Design
Other work in 2008 will include further experimental validation, and the investigation of soot pre-cursors, which is a prelude to the second phase, MFC-II.
The need for MFC-II was identified by the members of the consortium, said Rosenthal. Coming regulations will require greater prediction and control of particulate size and number. Of special growing medical concern are the very small particles below 1.0 µm in diameter.
Current soot models are insufficient for design and planning purposes for next-generation engines, fuels and aftertreatment systems. (One significant coming challenge will be the increasing presence fuels derived from unconventional petroleum sources, such as heavy oil, oil sands and shale, and coal.) They are only valid in very narrow ranges of operation, according to Rosenthal. They are not predictive, he said, and at worst can give wrong trends.
The goal of the work of MFC-II will be how to predict emissions, given the complexity of the emerging engine-fuel systems, to support the development of systems for lower engine-out emissions and thus to reduce the cost of aftertreatment. Better simulation will allow accurate, full system-level emulation, said Rosenthal.
|Multi-zone engine model. Click to enlarge.
CHEMKIN-PRO and HCCI. With the release of CHEMKIN-PRO (earlier post), Reaction Design delivered a massive speed improvement that enables the use of more accurate chemistry in more demanding applications.
Combined with a multi-zone engine model, the enhanced-performance CHEMKIN-PRO now can be used for modeling HCCI (homogeneous charge compression ignition) combustion in parametric what-if studies. An intriguing application in the future could be the on-board deployment of a CHEMKIN module combined with an in-tank fuel sensor. Such a system could analyze the actual fuel content, then apply an appropriate model, the results of which could, in turn, inform the combustion management system for an HCCI engine. The result would be HCCI operation optimized for fuel properties and operating conditions, Rosenthal suggested.