Flamelet Generated Manifolds Applied to Dual-Fuel Combustion of Lean Methane/Air Mixtures at Engine Relevant Conditions Ignited by n Dodecane Micro Pilot Sprays

In this study, a novel 3D-CFD combustion model employing Flamelet Generated Manifolds (FGM) for dual fuel combustion was developed. Validation of the platform was carried out using recent experimental results from an optically accessible Rapid Compression Expansion Machine (RCEM). Methane and n-dodecane were used as model fuels to remove any uncertainties in terms of fuel composition. The model used a tabulated chemistry approach employing a reaction mechanism of 130 species and 2399 reactions and was able to capture non-premixed auto ignition of the pilot fuel as well as premixed flame propagation of the background mixture. The CFD model was found to predict well all phases of the dual fuel combustion process: I) the pilot fuel ignition delay, II) the Heat Release Rate of the partially premixed conversion of the micro pilot spray with entrained methane/air and III) the sustained background mixture combustion following the consumption of the spray plume. The test conditions on the RCEM were chosen to mimic engine relevant conditions with start of injection (SOI) pressure and temperature of 45 bar and 1000 K respectively. The reactivity of the background lean mixture was varied by changing the air to fuel ratio λ; values of 2.1, 3 and ∞ (i.e. pure diesel) were tested. The model shows considerable promise as it was able to reasonably predict the effects of changing the reactivity of the background mixture as per measured from the RCEM experiments. To the authors best knowledge, this is the first study in the open literature reporting on the application of FGM to dual-fuel combustion of lean premixed methane/air charges ignited with liquid micro pilot fuel sprays.