Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeremy Worm

Committee Member 1

Jeffery Allen

Committee Member 2

Scott Miers


Vehicle emissions standards are becoming increasingly more strict as time progresses. Once all of the emissions devices are in their operational stage, these standards can be met with reasonable effort in powertrain design and calibration. However, the core of this system, the three-way catalyst, is non-operational until it has reached 200-350⁰C. Because of this, cold-start catalyst heating is extremely important in new vehicles. The objective of this project was to improve catalyst heating without increasing engine-out emissions. It was decided that the sensible heat portion of the exhaust enthalpy would be the best metric to judge differences between the different strategies. This is because catalyst-in temperatures ignore the energy flow increase with an increase in mass flow and exergy relates to a state that simply doesn’t exist in application. The two strategies tested were the deactivation of one exhaust valve and an increase in exhaust cam duration. While neither strategy proved to be particularly effective on their own, the combination of both could be a viable option for increased exhaust enthalpy and a minimal increase in engine-out emissions. Interestingly, the key to these changes was mostly due to changes in the rebreathing of the engine.