Laminar flame speed prediction for Natural Gas/Hydrogen blends and application to the combustion modeling in IC Engines

Francesco Arpaia, Fabian Mauss

Abstract

Laminar flame speed prediction for Natural Gas/hydrogenIn recent years, air quality has become a severe problem in many countries. The use of natural gas as an alternative fuel has been growing in recent years, since it is a promising alternative fuel to meet strict engine emission regulation. Natural gas has the potential to provide a good compromise in cost, efficiency and emission when used in Internal Combustion Engines. Thanks to its higher resistance to auto-ignition, engine efficiency can be increased through the use of higher compression ratios. Its high H/C ratio thanks to its low carbon level leads to less carbon dioxide, carbon monoxide and hydrocarbon emissions compared to gasoline fuels. The lower peak combustion temperatures under lean conditions, in comparison to stoichiometric conditions, lead to a lower knock tendency. The main problem of this type of engines is that the methane burns quite slowly. This causes reduced thermal efficiency and increased fuel consumption, due to significant cycle-to-cycle variations and reduced power. This work investigates the prediction of laminar flame speed using 3D and 0D SI-SRM. To cope with that problem, different blends were studied, with specific reference to the addition of hydrogen. As the laminar flame speed is one of the most relevant parameters for the prediction of the combustion properties inside the engine cylinder, its evaluation has been the main target of this work. The laminar flame speed has been calculated with two different approaches. First the Freely Propagating Flame Module in LOGEresearch has been used, that performs combustion and chemical kinetics simulation for different surrogate composition. Second, the laminar flame speed for the single surrogate components has been calculated and applied in a new correlation tool to compose the flame speeds for the multicomponent surrogate. The flame speeds calculated with both approaches are stored in look-up tables and retrieved within the engine simulation. It is fundamental to choose a good kinetic mechanism and to validate it. It was found that an accurate evaluation of the laminar flame speed has been carried out for a wide range or pressure, temperature, EGR and Equivalence ratio. The generated and validated flame speed tables are applied in 3D and 0D engine simulations for further validation, considering IMEP and MFB50. blends and application to the combustion modeling in IC Engines.