Fundamental Study on High Temperature Chemistry
of Oxygenated Hydrocarbons as Alternate Motor Fuels and Additives
Joseph W. Bozzelli, New Jersey Institute of Technology
Experiments and model development are performed to understand fundamental reaction processes of oxygenated hydrocarbons: alcohols, ethers and esters important to combustion and gasoline octane blending. Detailed mechanisms are developed to allow optimization and trend prediction in engine performance and emission reduction.
Oxygenates, such as dimethyl ether, methanol and ethanol, are considered for use as additives in required oxygen containing fuels in many States. They also may serve as octane additives or alternative motor fuels. Methyl tertbutyl ether (MTBE), is widely used as an anti-knock component and oxygenate additive in gasolines. Experimental data on effects of operation parameters from fuels using oxygenates are needed to test and validate models. A model based on fundamental principles and tested against available experimental data should allow calculation of trends toward optimal fuel blends, performance, and emis-sion characteristics for further testing and optimization.
Method of Approach
Experimental: Gas mixtures are reacted in a variable pressure, high tempera-ture tubular flow reactor. Reactor effluent is analyzed for products as a function of temperature, residence time, and fuel equivalence ratio. Analysis is performed with on-line gas chromatography (GC), flame ionization detection (FID), Fourier Transform Infrared (FTIR) and GC / Mass Spectrometry. Modeling: Reaction mechanisms are built from elementary reactions with rate constants based upon fundamental principles of thermochemical kinetics, sta-tistical mechanics and transition state theory. Quantum Rice-Ramsperger--Kassel theory for k(E), modified strong collision treatment for fall-off and thermodynamic properties are used in chemical activation and unimolecular reactions for rate constants. Ab initio and density functional calculations at the G2, CBS-Q, CBS-q and QCISD(t)/6-311+g(d,p)//MP2/6-31+G(d,p) or //B3LYP/6-31+G(d,p) levels of theory are used to determine thermodynamic properties and transition state structures and energies.
Summary of Progress and Accomplishments
Relatively high level calculation theory (see above) for determining thermody-namic properties of molecules and transition states is implemented. Calcula-tions now use ab initio and density functional theory in place of semi-empiri-cal theory. A Number of complex reaction systems for hydrocarbon radical oxi-dation have been studies at CBS-Q, CBS-q and G2 levels of theory. These in-clude methyl-tertbutyl, dimethyl ether, tertbutyl, isobutenyl and isobutyl - radical reactions with oxygen.
Oxidation and pyrolysis experiments on MTBE oxidation from one to ten at-mospheres pressure, fuel equivalence ratios 0.7 to 1.5 are complete. Experi-ments on dimethyl ether oxidation at varied fuel equivalence ratios, 1 atm pressure are complete. A thermodynamic database and a pressure dependent elementary reaction mechanism has been assembled for MTBE oxidation and eval-uated against experimental data. Sub-models for oxidation of neopentane, iso-butane, and isobutene oxidation are developed and model data compare well with experiment. A pressure dependent reaction mechanism for oxidation of dimethyl ether is developed and tested on flow reactor experiments.
Interactions with Other CAO Projects
John Seinfeld: California Inst Technology These researchers developed and validated accuracy of the density functional / Complete Basis Set Method for calculating transition state energies and geometries. We are at present using a slight modification of their published method.
Jack Howard - MIT: Quantum RRK with modified Beta Collision and with Master Equation analysis were performed on reactions important in Benzene oxidation in supercritical water.
W. H. Green MIT &endash; Group additivity calculations for thermodynamic properties and intramolecular rotor contributions to entropies.
Status of Original Plan
Experiments are complete. The mechanisms are first generation and are partial-ly validated. They are undergoing further testing and development.
Calculation capabilities for thermodynamic and kinetic properties are now higher level than proposed.
Chiung-ju Chen, Takahiro Yamada, Chad Sheng
John Seinfeld, Caltech; Jack Howard, MIT
[Source and Control Projects] [Transport and Transformation Projects] [Monitoring and Source Attribution Project]