Oxidation of Fuels in the Cool Flame Regime for Combustion and Reforming for Fuel Cells.

Naidja, A.; Butcher, T.; Mahajan, Devinder

doi:10.2172/801420

Cited by 11 publications

(11 citation statements)

References 126 publications

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“…The phenomenon of negative temperature coefficient (NTC) is an essential feature of the oxidation kinetics of large hydrocarbons, and is closely related to such practically important phenomena and processes as low-temperature ignition [1], cool flames [2,3], flame stabilization [4], fuel processing [5], engine knock [6] and the development of HCCI (homogenous charge compression ignition) engines [7]. It refers to the effect that, for a given pressure and in an initial temperature regime much lower than the adiabatic flame temperature of the reacting mixture, the ignition delay could increase with increasing initial temperature.…”

Section: Introductionmentioning

confidence: 99%

On the controlling mechanism of the upper turnover states in the NTC regime

Zhao

et al. 2016

Combustion and Flame

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Using n-butane, n-heptane and iso-octane as representative fuels exhibiting NTC (negative temperature coefficient) behavior, comprehensive computational studies with detailed mechanisms and theoretical analysis were performed to investigate the upper stationary point, denoted as turnover states, on the NTC curve near the higher temperature regime, where the ignition delay τ exhibits a local maximum. It is found that the global behavior of the turnover states exhibits distinctive thermodynamic and kinetic characteristics under different pressures, in that the ignition delay at the turnover states shows an Arrhenius dependence on the temperature T and an approximate inverse quadratic power law dependence on the pressure P. These global behaviors imply that the temperature and pressure of the turnover states are not independent and can be correlated by an Arrhenius dependence, as ln P ∝ 1/T. Further theoretical analyses demonstrate that such turnover states result from the competition between the low-temperature chain branching reactions and the decomposition of the intermediate species, and therefore correspond to a critical value, α, of the ratio of OH production from low-temperature chemistry. In addition, the ignition delay at the turnover state can be well correlated by the analytical expression derived by Peters et al., with the further demonstration that the pressure dependence of the turnover ignition delay mainly result from the H 2 O 2 decomposition reaction. Comparison of the present results with the literature experimental data of n-heptane ignition delay time shows very good agreement.

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Section: Introductionmentioning

confidence: 99%

On the controlling mechanism of the upper turnover states in the NTC regime

Zhao

et al. 2016

Combustion and Flame

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“…The chemical ignition delay share considers the molecule chain breakup and the reaction, including the formation of free radicals. 21,22 To model this delay, a distinction between low-temperature and high-temperature kinetics of the diesel fuel conversion is made. To describe the behavior between the two paths, an additional weighting function needs to be introduced, according to equation (17).…”

Section: Ignition Delay Modelmentioning

confidence: 99%

Real-time capable simulation of diesel combustion processes for HiL applications

Neumann

Jörg

Peschke

et al. 2017

International Journal of Engine Research

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The complexity of the development processes for advanced diesel engines has significantly increased during the last decades. A further increase is to be expected, due to more restrictive emission legislations and new certification cycles. This trend leads to a higher time exposure at engine test benches, thus resulting in higher costs. To counter this problem, virtual engine development strategies are being increasingly used. To calibrate the complete powertrain and various driving situations, model in the loop and hardware in the loop concepts have become more important. The main effort in this context is the development of very accurate but also real-time capable engine models. Besides the correct modeling of ambient condition and driver behavior, the simulation of the combustion process is a major objective. The main challenge of modeling a diesel combustion process is the description of mixture formation, self-ignition and combustion as precisely as possible. For this purpose, this article introduces a novel combustion simulation approach that is capable of predicting various combustion properties of a diesel process. This includes the calculation of crank angle resolved combustion traces, such as heat release and other thermodynamic in-cylinder states. Furthermore, various combustion characteristics, such as combustion phasing, maximum gradients and engine-out temperature, are available as simulation output. All calculations are based on a physical zero-dimensional heat release model. The resulting reduction of the calibration effort and the improved model robustness are the major benefits in comparison to conventional data-driven combustion models. The calibration parameters directly refer to geometric and thermodynamic properties of a given engine configuration. Main input variables to the model are the fuel injection profile and air path-related states such as exhaust gas recirculation rate and boost pressure. Thus, multiple injection event strategies or novel air path control structures for future engine control concepts can be analyzed.

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“…A threefluid nozzle for fuel atomisation and educt mixing is used by Argonne National Laboratory [4]. The so-called cool flame [5] is used as a heat source needed for fuel evaporation in the reformer mixing chamber of the Oel-Wärme Institut GmbH [6].…”

Section: Reformer Developmentmentioning

confidence: 99%

Optimised Mixture Formation for Diesel Fuel Processing

et al. 2008

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Mixture formation plays an important role in the diesel reforming process. It is important to maintain proper O2/C and H2O/C ratios to avoid hot spots and coking. Fuel must be completely evaporated before entering the reaction zone in order to prevent catalyst damage by coking. Computational fluid dynamics (CFD) is used to optimise the mixing process. Turbulent mixing, diesel spray injections and evaporation and simplified chemical reactions have been calculated. This revealed critical parts of the existing construction. However, experimental verification is necessary. To identify thermodynamic conditions for a possible carbon formation process, experiments with idealised model fuels as well as with real diesel fuel were carried out. Flow visualisation experiments serve for the verification of the CFD simulations. Quartz glass reactors as models of the reformers were operated under real mixing temperatures (400 °C) to observe the effect of the flow profile on fuel sprays. Experiments with coloured fuels were used to visualise the flow and concentration profiles in the mixing chamber. Results were compared with CFD models. Two patented reformers were designed as a result of the CFD optimisation. These were operated for 500 h and 1,000 h respectively with a commercially available diesel, showing very promising results.

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Oxidation of Fuels in the Cool Flame Regime for Combustion and Reforming for Fuel Cells.

Cited by 11 publications

References 126 publications

On the controlling mechanism of the upper turnover states in the NTC regime

On the controlling mechanism of the upper turnover states in the NTC regime

Real-time capable simulation of diesel combustion processes for HiL applications

Optimised Mixture Formation for Diesel Fuel Processing

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