Conference Paper

Combustion Kinetics of Conventional and Alternative Jet Fuels using a Hybrid Chemistry (HyChem) Approach

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Abstract

With increasing use of alternative fuels, approaches that can efficiently model their combustion chemistry are essential to facilitate their utilization. The hybrid chemistry (HyChem) method incorporates a basic understanding about the combustion chemistry of multicomponent liquid fuels that overcomes some of the limitations of the surrogate fuel approach. The present work focused on a comparative study of one conventional, petroleum-derived Jet A fuel (designated as A2), with an alternative, bio-derived fuel (designated as C1), using a variety of experimental techniques as well as HyChem modeling. While A2 is composed of a mixture of n-, iso-, and cyclo-alkanes, and aromatics, C1 is composed primarily of two highly branched C12 and C16 alkanes. Upon decomposition, A2 produces primarily ethylene and propene, while C1 produces mostly isobutene. HyChem models were developed for each fuel, using both shock tube and flow reactor speciation data. The developed models were tested against a wide range of experimental data, including shock tube ignition delay time and laminar flame speed. The stringent validations and agreement between the models and experimental measurements highlight the validity as well as potential wider applications of the HyChem concept in studying combustion chemistry of liquid hydrocarbon fuels.

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... More recently, Wang and co-workers [5][6][7][8][9][10][11] proposed a hybrid chemistry (HyChem) reduction model based on this decoupling. For fuel pyrolysis, Wang et al. [5][6][7][8][9][10][11] proposed a lumped model represented by a set of global steps for C-C fission and radical abstraction reactions. ...
... More recently, Wang and co-workers [5][6][7][8][9][10][11] proposed a hybrid chemistry (HyChem) reduction model based on this decoupling. For fuel pyrolysis, Wang et al. [5][6][7][8][9][10][11] proposed a lumped model represented by a set of global steps for C-C fission and radical abstraction reactions. The second step representing oxidation is modeled using a foundational C 0 -C 4 chemistry mechanism to describe the oxidation of fuel fragments. ...
... While the HyChem approach [5][6][7][8][9][10][11] represents an efficient strategy for chemistry reduction of complex fuels, other approaches built on the same premises may be adopted with potential advantages and drawbacks. One of the motivations towards exploring additional strategies is whether useful information can be extracted directly from temporal measurements for key fragments, albeit potentially noisy, in shock tubes. ...
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The oxidation chemistry of complex hydrocarbons involves large mechanisms with hundreds or thousands of chemical species and reactions. For practical applications and computational ease, it is desirable to reduce their chemistry. To this end, high-temperature fuel oxidation for large carbon number fuels may be described as comprising two steps, fuel pyrolysis and small species oxidation. Such an approach has recently been adopted as ‘hybrid chemistry’ or HyChem to handle high-temperature chemistry of jet fuels by utilizing time-series measurements of pyrolysis products. In the approach proposed here, a shallow Artificial Neural Network (ANN) is used to fit temporal profiles of fuel fragments to directly extract chemical reaction rate information. This information is then correlated with the species concentrations to build an ANN-based model for the fragments’ chemistry during the pyrolysis stage. Finally, this model is combined with a C0-C4 chemical mechanism to model high-temperature fuel oxidation. This new hybrid chemistry approach is demonstrated using homogeneous chemistry calculations of n-dodecane (n-C12H26) oxidation. The experimental uncertainty is simulated by introducing realistic noise in the data. The comparison shows a good agreement between the proposed ANN hybrid chemistry approach and detailed chemistry results.
... The oxidation and pyrolysis experiments of the blended fuels were conducted in a variable pressure flow reactor and shock tube facilities, respectively. Detailed descriptions of the two reactors can be found in an accompanying study[8]. The blended fuels were prepared by volumetrically mixing A2 and C1 fuels with a pipette. ...
... To avoid mixing effects in the entrance of the flow reactor, Chemkin simulations were started at around 3 ms of reaction time. All species measured at that reaction time were used as input.Similar to the neat fuel results[8], both the predictions and experiment show that the fuel decay of C1 in the blends is faster than A2. Furthermore, the decomposition rate of each fuel scales with blend mole ratios relative to the neat fuels. ...
Conference Paper
The hybrid chemistry modeling approach, termed HyChem, was used to explore the combustion chemistry of blended petroleum and bio-derived jet fuels. The pyrolysis products of conventional petroleum derived-fuels, such as Jet A, are dominated by ethylene and propene, whereas in many bio-derived fuels, such as alcohol to jet (ATJ) fuels, the fuel comprises highly branched alkanes and produces isobutene as a main pyrolysis product. We report here an investigation of blends of Jet A (designated A2) and an ATJ fuel (designated C1) with the central question of whether the HyChem models for neat fuels can be combined to model the blend combustion behaviors. The pyrolysis and oxidation of several blends of A2 and C1 were investigated. Flow reactor experiments were carried out at 1 atm, 1030 and 1140K, with equivalence ratios of 1.0 and 2.0. Shock tube measurements of blended fuel pyrolysis were performed at 1 atm from 1025 to 1325 K. Good agreement between measurements and model predictions was found showing that formation of the products in the blended fuels were predicted by a simple combination of the HyChem models for the two individual fuels, thus demonstrating that the HyChem models for two jet fuels of very different compositions are “additive.”
... Hybrid chemical models, such as the HyChem model introduced by Wang et al. [84], have been chemical mechanism, high-temperature n-dodecane oxidation chemistry was obtained. The ANN-based hybrid chemistry showed a good agreement with the detailed chemistry. ...
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Development of an experimental database and kinetic models for surrogate jet fuels
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On liquid real-fuel combustion kinetics – I. theory and analysis
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