(684b) Shock Tube Study of Co-Optima Biofuels Combustion

Global consumption of fossil fuels and the production of greenhouse gases continues to rise, causing deleterious effects to the environment and all its inhabitants. The transportation sector is one of the largest culprits in greenhouse gas emissions— in 2017, 29% of all energy consumed in the U.S. was by the transportation industry and 89% of that energy came from petroleum based fuels [1]. In order to curb these increasing levels of greenhouse gases while still meeting the world’s energy demands, alternative fuels are essential. The Co-Optimization of Biofuels and Engines (Co-Optima) has sought such alternatives in biofuels, because they are readily produced in large quantities through renewable means, have the potential to decrease greenhouse gases compared to petroleum based fuels, and may even provide similar energy outputs to gasoline. Co-Optima have identified several biofuels of various chemical classes, which show potential to be used in future engines to increase fuel economy and efficiency while decreasing greenhouse gases. However, before any of the identified fuels can be consumed by the general public, well-validated chemical kinetic mechanisms must be constructed so that the complete reactivity and behavior of these fuels is understood.

Validating kinetic mechanisms requires experimental data which is easily obtained in a shock tube—a device that simulates engine relevant conditions via gas compression from shock waves. Using this device, ignition delay time and species time-histories can be obtained during the fuel decomposition under engine relevant conditions and compared to the outputs of these kinetic mechanisms. Valuable molecules for time-history comparisons include carbon monoxide, ethylene, and formaldehyde. Carbon monoxide and ethylene are important because in hydrocarbon decomposition, these are two of the most abundant molecules formed and in oxidation processes carbon monoxide is the direct pathway for carbon dioxide formation, the major contributor to elevating global temperatures. Formaldehyde is also an important intermediate because it is an essential pathway for many of the major species formed through hydrocarbon decomposition. Therefore, in this work the Co-Optima fuels 2,4,4-trimethyl-1-pentene, prenol, isoprenol, cyclopentanone, and methyl propyl ether are investigated behind reflected shockwaves to obtain these key parameters for mechanism validation.

The conditions and data collected for each fuel varies depending on the validation targets needed for each specific fuel. 2,4,4-trimethyl-1-pentene is investigated between 1186-1414 K at 9.5 atm and an equivalence ratio of 1.0, ignition delay times and carbon monoxide time-histories are reported. Prenol and isoprenol are studied between 1269-1472 K at 9.4 atm and an equivalence ratio of 1.0. Cyclopentanone oxidation and pyrolysis have been examined, carbon monoxide time-histories and ignition delay times are collected during the oxidation of cyclopentanone and conditions span a temperature range of 1165-1327 K at pressures of 1, 6, and 8.5 atm. For cyclopentanone pyrolysis, the fuel depletion and formation of carbon monoxide and ethylene are measured at conditions of 9.5 atm and 1079-1393 K. The oxidation and pyrolysis of methyl propyl ether (MPE) has also been investigated. Formaldehyde time-histories were measured during the pyrolysis of MPE and spanned conditions of 1180-1474 K at pressure near 2.5 atm. During MPE oxidation, carbon monoxide time-histories and ignition delay times were recorded at conditions of 1313-1511 K and 9.5 atm. Data for all species are compared to their respective kinetic mechanisms previous available in the literature or preliminary mechanisms that are being developed for the Co-Optima program. Discrepancies between the experimental and theoretical data are highlighted, and where appropriate, suggestions are offered for changes in kinetic rates.

1-Administration, U.S.E.I., 2017. https://www.eia.gov/energyexplained/?page=us_energy_transportation