(214h) From Electrons to Engines: Kinetic Modeling of Low-Temperature Hydrocarbon Oxidation and Applications in Engine and Atmospheric Chemistry

From Electrons to Engines:
Kinetic Modeling of Low-Temperature Hydrocarbon Oxidation and Applications in Engine and Atmospheric Chemistry

Amrit Jalan and William H. Green

Department of Chemical Engineering, 77 Massachusetts Avenue, Room E18-566A, Cambridge, MA 02139, USA E-mail: whgreen@mit.edu

The chemistry of hydrocarbon oxidation at temperatures below ~800 K lies at the heart of several technological and natural phenomena. Examples include:

1. Aging/thermal stability: Oxidative degradation of polymers, fuels, biological lipids, etc. which are directly responsible for clogging arteries and fuel injectors alike.
2. Energy: Clean engine concepts like homogeneous charge compression ignition (HCCI) which rely on low-temperature auto-ignition to lower soot formation and NO_x emissions.
3. Climate: Atmospheric fate of organic material including processes like alkene ozonolysis and secondary organic aerosol formation.
4. Bulk Chemicals: Industrial oxidation processes used to manufacture chemicals like nylon, terephthalic acid and phenol, typically performed at low temperatures in solvent media.

Consequently, low-temperature oxidation has been the subject of experimental investigations for many decades. However, it is difficult to understand these processes at a mechanistic level from experiments alone for reasons like complex product mixtures which are difficult to analyze (e.g. liquid phase oxidation) or inherent instability of key reaction intermediates (like the Criegee Intermediate (CI) in alkene ozonolysis). Over the past 20 years, developments in scientific computing have opened up computational chemistry and chemical engineering tools as an attractive option for exploring and elucidating the kinetics of these complex processes.

In this work, we combine high-level electronic structure theory, reaction rate theory, automated kinetic modeling and empirical correlations for multi-scale modeling of low-temperature liquid phase oxidation and its application in modeling deposit formation in diesel fuel-injectors. We demonstrate the application of molecular modeling and engineering in the following areas:

1. Elementary reaction kinetics:
   • Use of quantum chemistry to explore new pathways for carboxylic acid formation in liquid-phase oxidation confirming a 30-year old experimental hypothesis.
   • Applications of similar pathways in atmospheric reactions of the Criegee Intermediate with carbonyl compounds.
2. Reaction network analysis:
   Use of automatic network generation to identify and resolve discrepancies between textbook models and experimental data on liquid phase oxidation.
3. Coupled kinetics/phase equilibrium
   Combine elementary kinetics with empirical phase-separation and transport models to simulate and investigate the mechanism of deposit formation in fuel injectors.