Dual Fuel Reaction Mechanism 2.0 including NOx Formation and Laminar Flame Speed Calculations Using Methane/Propane/n-Heptane Fuel Blends

Abstract

This study presents the further development of the TU Wien dual fuel mechanism, which was optimized for simulating ignition and combustion in a rapid compression expansion machine (RCEM) in dual fuel mode using diesel and natural gas at pressures higher than 60 bar at the start of injection. The mechanism is based on the Complete San Diego mechanism with n-heptane extension and was attuned to the RCEM measurements to achieve high agreement between experiments and simulation. This resulted in a specific application area. To obtain a mechanism for a wider parameter range, the Arrhenius parameter changes performed were analyzed and updated. Furthermore, the San Diego nitrogen sub-mechanism was added to consider NO x formation. The ignition delay time-reducing effect of propane addition to methane was closely examined and improved. To investigate the propagation of the flame front, the laminar flame speed of methane-air mixtures was simulated and compared with measured values from literature. Deviations at stoichiometric and fuel-rich conditions were found and by further mechanism optimization reduced significantly. To be able to justify the parameter changes performed, the resulting reaction rate coefficients were compared with data from the National Institute of Standards and Technology chemical kinetics database.Energies 2020, 13, 778 2 of 31 in the simulation would lead to an unmanageable simulation time. Therefore, surrogate fuels were defined for the simulation. n-heptane is a common diesel substitute in dual fuel investigations [8][9][10] and was used as a surrogate. It is therefore well suited as diesel substitute, since with a cetane number (which describes the flammability of the fuel) of 56 [11], n-heptane is in the range of the diesel cetane number, which has to be 51 or higher according to the DIN EN590 standard of October 2009. In analogy to diesel fuel, it is necessary to define a substitute fuel for natural gas. A frequently used substitute fuel is methane [8,10]. To better reflect the methane number (which is a measure of the knock resistance) of natural gas, a mixture of methane and propane was defined as a surrogate. In [7], in the first step, the ignition delay times (IDTs) of homogeneous methane-propane-n-heptane mixtures were investigated with a rapid compression machine (RCM) and a shock tube (ST) at PCFC (Physico Chemical Fundamentals of Combustion), RWTH Aachen [12,13], followed by the comparison of the measured values with simulation results using various n-heptane mechanisms available in the literature. For the simulations in [7], as well as the actual study, the program LOGEresearch (Version LSv1.09, LOGE AB, Lund, Sweden) [14] was used. The simulation of the RCM measurements was performed with the module "rapid compression machine" in LOGEresearch at a specific fuel composition, fuel-air equivalence ratio, starting temperature, and starting pressure of the mixture before compression. The RCM facility effects describe the non-ideal behavior of the test facility and the machine-specific com...

Optimization of the Pd-Catalyzed Alkylation of the Fermentation-Derived Oxygenates Acetone and Butanol toward Sustainable Aviation Fuel (SAF) Intermediates

“…C7 was predominantly obtained over C11 under conditions with lower T , higher C , or lower B . The resulting alkane, n -heptane, is commonly used as a zero-point reference for engine testing (octane number of 0) being an undesired component in gasoline given its knocking fuel behavior, while it can be blended with diesel fuels as its cetane number of 56 falls in the range of suitable diesel fuel performance (cetane number of 51 or higher) . C7 itself can however also be used as a specialty chemical, most notably in the food and agricultural sectors as a food additive or pesticide .…”

“…The resulting alkane, n-heptane, is commonly used as a zero-point reference for engine testing (octane number of 0) being an undesired component in gasoline given its knocking fuel behavior, 37 while it can be blended with diesel fuels as its cetane number of 56 falls in the range of suitable diesel fuel performance (cetane number of 51 or higher). 38 C7 itself can however also be used as a specialty chemical, most notably in the food and agricultural sectors as a food additive 39 or pesticide. 40 Considering this potential, it could be possible to either aim for those conditions where C7 is predominantly produced or aim to separate C7 from C11 for its further utilization as a side product.…”