<p>Three dimensional (3D) computational fluid dynamics (CFD) engine simulations can guide and/or complement experimental investigations, and to provide in-cylinder details that conventional data acquisition methods cannot capture. The main objective of this study was to establish a 3D RANS model (i.e., reasonable computational costs and running times) that can predict a compression ignition engine’s efficiency and emissions for various operating conditions. The sub-models include RNG k-epsilon turbulence model, G-equation model, solid cone breakup model (including KH-RT model ad gas jet model), two-step model, and etc. The model was validated with experimental data from a heavy duty single cylinder diesel engine. Using a unique set of model tuning parameters, the model was able to qualitatively predict engine performance and emissions over a range of operating conditions that changed injection timing, excess air ratio, and engine speed. A simulated altitude test was also conducted using the calibrated 3D mesh model. The results indicated the numerical model captured the combustion and emissions characteristics at high altitude, suggesting its capability of evaluating the properties of engines in the plateau regions. In detail, the results present reduced cylinder pressure, higher engine temperature, increased and retarded maximum pressure rise rate (or maximum apparent heat release rate), slightly longer ignition delay, delayed end of combustion, extended combustion duration, lower engine power output, and decreased engine efficiency, when operated at high altitude. Moreover, the simulation results indicated an enhanced penetration capability of the fuel injection sprays with the elevation of altitude. In detail, the decrease of the in-cylinder density caused smaller droplet size, which led to coalescence reduction. This lower coalescence reduced jet-to-wall impingement, but the lower density also decreased the spray angle thus leading to increased spray penetration. The increased wall impingement of the fuel droplets contributed to an uneven distribution of the mixture concentration and combustion deterioration in the cylinder. As a result, the rise in altitude led to a reduction in efficiency and an increment of incomplete combustion production concentrations. Overall, the effects of altitude on engine combustion and performance can be summarized as two aspects. First comes the extended ignition delay at high altitude, which would raise the pressure rise rate to a point that can exceed the maximum allowable limit and therefore shorten the engine lifespan. The other disadvantage of high-altitude operation is the reduced excess air ratio and gas density inside cylinder at high altitude. Worsened spray formation and mixture preparation, together with insufficient late oxidation, would result in reduced engine efficiency, increased emissions, and power loss.</p>

Three-Dimensional Computational Fluid Dynamics Modeling of a 6V150 Diesel Engine

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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