The aim of this study was to determine possibilities of the soot and NOx emissions reduction from an existing heavy-duty compression-ignition (CI) engine based only on in-cylinder techniques. To that end numerical simulations of such processes as a multiphase fuel flow through injector nozzles, a liquid fuel jet breakup and evaporation, combustion and emissions formation were performed in AVL Fire 3D CFD software. The combustion process was calculated with the ECFM-3Z model and with the detailed n-heptane oxidation scheme that consisted of 76 species and 349 reactions. Both approaches of combustion modeling were validated against experimental data from the existing engine working under 75% and 100% loads. As for the reduction of the NOx emission an introduction of exhaust gas recirculation (EGR) was investigated. As for the soot concentration reduction such measures as an increased rail pressure, application of a post-injection and an increased injector nozzles conicity were investigated. Finally the ECFM-3Z model with emissions models, as well as the n-heptane mechanism predicted that it is possible to reach specified emissions limits with application of EGR, post-injection and increased nozzles conicity.
This research encompasses the numerical analysis of trioxymethylene dimethyl ether (OME-3) e-fuel on an industrial compression ignition engine, as a viable replacement for diesel fuel. The performed simulations examined single injection and multi injection operating conditions of OME-3, varying injection rates and timing. The combustion process is modelled employing two approaches: three-dimensional Extended Coherent Flame Model (ECFM-3Z) and General Gas Phase Reactions (GGPR) with the reduced chemical kinetic mechanism. ECFM-3Z gives a faster convergence, where pretabulated autoignition and laminar flame speed databases are integrated into the model to decrease computational time. GGPR approach is validated on the experimental values for mean pressure, temperature, and rate of released heat in the same engine with diesel fuel and then again on an OME-3. Both approaches confirmed that a higher amount of OME-3 and a longer injection time is needed to achieve equivalent output power as diesel fuel since OME-3 has a lower net calorific value. It is established that multi injection case with an adapted injection timing is the optimal choice for OME-3 combustion since it achieves a 15% higher mean pressure peak compared to the diesel case. Nitrogen oxides emissions for OME-3 are also compared to the diesel case for both combustion modelling approaches.
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