An experimental and modeling study of diethyl carbonate oxidation

Diethyl carbonate (DEC) is an attractive biofuel that can be used to displace petroleum-derived diesel fuel, thereby reducing CO2 and particulate emissions from diesel engines. A better understanding of DEC combustion characteristics is needed to facilitate its use in internal combustion engines. Toward this goal, ignition delay times for DEC were measured at conditions relevant to internal combustion engines using a rapid compression machine (RCM) and a shock tube. The experimental conditions investigated covered a wide range of temperatures (660-1300K), a pressure of 30bar, and equivalence ratios of 0.5, 1.0 and 2.0 in air. To provide further understanding of the intermediates formed in DEC oxidation, species concentrations were measured in a jet-stirred reactor at 10atm over a temperature range of 500-1200K and at equivalence ratios of 0.5, 1.0 and 2.0. These experimental measurements were used to aid the development and validation of a chemical kinetic model for DEC.The experimental results for ignition in the RCM showed near negative temperature coefficient (NTC) behavior. Six-membered alkylperoxy radical (RO˙2) isomerizations are conventionally thought to initiate low-temperature branching reactions responsible for NTC behavior, but DEC has no such possible 6- and 7-membered ring isomerizations. However, its molecular structure allows for 5-, 8- and 9-membered ring RO˙2 isomerizations. To provide accurate rate constants for these ring structures, ab initio computations for RO˙2⇌Q˙OOH isomerization reactions were performed. These new RO˙2 isomerization rate constants have been implemented in a chemical kinetic model for DEC oxidation. The model simulations have been compared with ignition delay times measured in the RCM near the NTC region. Results of the simulation were also compared with experimental results for ignition in the high-temperature region and for species concentrations in the jet-stirred reactor. Chemical kinetic insights into the oxidation of DEC were made using these experimental and modeling results.

Citation

Nakamura, H., Curran, H. J., Polo Córdoba, A., Pitz, W. J., Dagaut, P., Togbé, C., … Bustamante, F. (2015). An experimental and modeling study of diethyl carbonate oxidation. Combustion and Flame, 162(4), 1395–1405. doi:10.1016/j.combustflame.2014.11.002

Acknowledgements

This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The work at LLNL work was supported by the US Department of Energy, Office of Vehicle Technologies and the Office of Basic Energy Sciences, and the authors thank program managers Gurpreet Singh, Kevin Stork, and Wade Sisk. The work performed at CNRS was funded via the ERC Advanced Grant "2G-CSafe: Combustion of Sustainable Alternative Fuels for Engines used in aeronautics and automotives", Grant Agreement Number 291049 (PI Philippe Dagaut). Co-author SMS acknowledges fellowship support from NSERC of Canada and from the KAUST Clean Combustion Research Center. Co-author ADPC acknowledges the Ministry of Agriculture, the Government of Cesar, Colciencias, Popular University of Cesar and the University of Antioquia in Colombia, for the doctoral scholarship received. Co-author HN acknowledges the financial support "Young Researcher Overseas Visits Program for Vitalizing Brain Circulation" from Japan Society for the Promotion of Science.