Exhaust Gas and Aftertreatment Modeling

Exhaust Gas and Aftertreatment Modeling

Abstract:
While the diesel (compression ignition) engine is more efficient than the conventional spark ignition engine from a thermodynamics standpoint, it has the potential for a large negative environmental impact. The lean combustion of these devices provides the perfect environment for the production of NOx; relatively high temperatures and abundant oxygen. In addition, direct injection of fuel into the combustion chamber creates rich fuel pockets that can cause the formation of particulate matter (soot). Recently these emissions have come under increased scrutiny from the Environmental Protection Agency (EPA). Their radical nature (smog) in the atmosphere and subsequent health hazards has caused the EPA to act to increase the regulation standards for both 2007 and 2010.

Unlike the three-way catalysts currently used on spark-ignition based platforms, diesel aftertreatment systems will not utilize one device for all problematic emissions. Instead, devices are targeted to take care of only one or a few issues at a time. For instance, Diesel Particulate Filters (DPF) might take care of the particulate matter while a Diesel Oxidation Catalyst (DOC) will eliminate the CO and HC and a Lean NOx Trap is used for the NOx emissions. Until now, diesel engine manufacturers have been able to meet the legislation though in-cylinder technology. The proposed EPA legislation has caused the diesel industry to work on finding cost-efficient aftertreatment technology while still looking in-cylinder for improvements.

Goal:
To accurately model the exhaust gas dynamics of an internal combustion engine including the ability to track the chemical species resulting from in-cylinder process and account for homogeneous reactions occurring. Heat transfer to/from the gas and the pipe walls will be modeled along with the outside environmental influences. Aftertreatment models for all possible catalytic and particulate filter devices will be included with the gas dynamics gas in a Matlab SIMULINK environment to provide a complete exhaust simulation. Optimization of the complete system will be accomplished to maximize the efficiency of each device and minimize the amount of problematic emissions.

Diesel Particulate Filter

Urea Aftertreatment

Researchers:
Dennis Assanis
Chaitanya Sampara

Sponsors:
General Motors Corporation
Eaton Corporation
Automotive Research Center (U.S. Army TACOM)

Achievements:
Accurate and fast variable-property reacting-gas dynamics solvers have been created for the basis of the exhaust flow and aftertreatment devices. Windows-based GUIs are used to speed up development time through the direct incorporation of the post-processing of the output. In addition, these GUIs allow other researchers to use the simulations with a minimum of start-up time. Matlab SIMULINK based models have also been created and optimization of specific devices is currently on-going.