Abstract
ϕ-sensitivity is the change in ignition delay time (IDT) with respect to the fuel-to-air equivalence ratio (ϕ). High ϕ-sensitivity is a desirable fuel property for applications in advanced compression ignition and multi-mode engine designs. Understanding how ϕ-sensitivity depends on chemical structure is essential for selecting promising biofuels from the ever-growing list of proposed candidates. In this study, we investigate the effect of chemical structure on ϕ-sensitivity with experiment, simulation, and theory. Experimental Advanced Fuel Ignition Delay Analyzer (AFIDA) measurements for 2,4-dimethylpentane and diisopropyl ether provide evidence that branching and functional groups strongly impact ϕ-sensitivity. Further insights into this dependence are obtained with 0-D kinetic simulations with existing mechanisms for n-pentane, diethyl ether, 3-pentanone, n-heptane, 2-methylhexane, 2,4-dimethylpentane, and 2,2,3-trimethylbutane. Quantum mechanical (QM) G4 calculations of low-temperature reactions help explain the observed experimental and simulation trends. Specifically, these QM calculations provide theoretical estimates of the ketohydroperoxide (KHP) dissociation rates, the HO2 formation rates from peroxy radical (ROO), and the “cross-over” temperatures, i.e., the temperature at which ROO dissociation is favored compared to hydroperoxyl radical (QOOH) formation. Each of these reaction rates is compared to the n-alkane reference point to determine the impact of branching and different functional groups. Although kinetic mechanisms typically assume that KHP dissociation rates are invariant of chemical environment, our QM results suggest that this rate can span a range of roughly two orders of magnitude. We also discuss the importance of including the peroxy-hydroperoxy (OO-OOH) hydrogen transfer reaction for branched ethers. Finally, the insights gained assist in proposing a highly ϕ-sensitive compound, namely, isopropyl propyl ether.
| Original language | English |
|---|---|
| Pages (from-to) | 377-387 |
| Number of pages | 11 |
| Journal | Combustion and Flame |
| Volume | 225 |
| DOIs | |
| State | Published - Mar 2021 |
| Externally published | Yes |
Funding
We would like to acknowledge Mark Nimlos of National Renewable Energy Laboratory (NREL) for his assistance in computing quantum mechanical rate coefficients, Andrei Kazakov of the National Institute of Standards and Technology (NIST) for invaluable discussions regarding low-temperature chemistry, and Charles Westbrook of Lawrence Livermore National Laboratory (LLNL) for providing the LLNL mechanisms. All of the 0-D simulations and quantum mechanical calculations were run on Eagle, the National Renewable Energy Laboratory high-performance computing system. This work was authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract no. DE347AC36-99GO10337. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes. A portion of this research was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies and Vehicle Technologies Offices DE-EE0007983. This work was authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract no. DE347AC36-99GO10337 . Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Bioenergy Technologies Office. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes. A portion of this research was conducted as part of the Co-Optimization of Fuels & Engines (Co-Optima) project sponsored by the U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies and Vehicle Technologies Offices DE-EE0007983.
| Funders | Funder number |
|---|---|
| Co-Optimization of Fuels & Engines | |
| U.S. Department of Energy Office of Energy Efficiency and Renewable Energy BioEnergy Technologies Office | |
| U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies | DE-EE0007983 |
| U.S. Government | |
| U.S. Department of Energy | DE347AC36-99GO10337 |
| National Renewable Energy Laboratory |
Keywords
- Computational chemistry
- Fuel properties
- Fuel-to-air equivalence ratio
- Kinetic mechanisms
- Low-temperature combustion
