|M.Sc Student||Faingold Galia|
|Subject||CFD Modeling of a Direct Injection H2/DME Fueled Internal|
|Department||Department of Mechanical Engineering||Supervisors||Professor Steven Howard Frankel|
|Dr. Leonid Tartakovsky|
|Full Thesis text|
Research efforts to produce more efficient, cleaner, and stable internal combustion engines are ongoing. Alternative, low carbon intensity fuels such as biomass or hydrogen, or fuel blends are being considered for the next generation of engines. Homogeneous charge compression ignition (HCCI) engines burning hydrogen with dimethyl ether (DME) additives are being studied at the Technion.
The effects of stratified reactivity and DME combustion characteristics in an HCCI engine were explored using a series of numeric studies. The purpose of the first series of simulations is to gage the ability of the commercial software CONVERGETM to reproduce the flame structure and species involved in the combustion of DME. The flamelet approach, which includes turbulence-chemistry interactions, was more accurate both in the reproduction of temperature levels and location of flame front. The detailed chemistry model over-predicted flame temperatures and influences the velocity field and flame locations. The more resolved, LES methods yield a better reproduction of experimental data when compared to the more modeled RANS simulations.
The same advantage was apparent when simulating the flow field and mixture propagation in an engine cylinder with gaseous direct injection. Simulation results were compared to measured data from an optically accessible engine at motoring conditions. LES results showed an overall better mixing of the injected fuel, similar to measured data. The injected fuel jet in the RANS simulation showed less break-up and was ultimately less mixed, so when modeling combustion in a cylinder this would introduce a further error pertaining to the distribution of fuel. A full engine cycle of an HCCI engine with stratified reactivity was simulated using the validated methods to gain phenomenological insight into the physical processes involved in stratified reactivity combustion. The additional 3D and turbulence considerations had a great impact on simulation results, replicating the pressure oscillations typical of HCCI combustion.