Dimethyl ether (DME) represents a promising fuel for heavy-duty engines thanks to its high cetane number, volatility, absence of aromatics, reduced tank-to-wheel CO2 emissions compared to Diesel fuel and the possibility to be produced from renewable energy sources. However, optimization of compression-ignition engines fueled with DME requires suitable computational tools to design dedicated injection and combustion systems: reduced injection pressures and increased nozzle diameters are expected compared to conventional Diesel engines, which influences both the air-fuel mixing and the combustion process.
This work intends to evaluate the validity of two different combustion models for the prediction of performance and pollutant emissions in compression-ignition engines operating with DME. The first one is the Representative Interactive Flamelet while the second is the Approximated Diffusive Flamelet. Both incorporate detailed kinetics and turbulence chemistry interaction but they are different in the way they account for mixing and flow conditions. A base case was simulated, comparing Diesel and DME before moving to an extensive validation of several different operating points of interest with variations of injection pressure, start of injection, engine speed and load. Analysis of the flame structure and validation with the experimental data of in-cylinder pressure and pollutant emissions will allow identifying the most suitable model for combustion simulations in DME compression-ignition engines. Finally, a new geometry for the piston bowl was tested with the validated numerical setup, evaluating the pros and cons associated with it.