Thermal efficiency improvement of PODE/Gasoline dual-fuel RCCI high load operation with EGR and air dilution

In recent years, polyoxymethylene dimethyl ethers (PODE) is used for reactivity gradient enlargement in direct injection engines due to its high Cetane Number (CN). In the current study, thermal efficiency improvement of PODE/Gasoline dual-fuel reactivity controlled compression ignition (RCCI) high load operation with exhausted gas recirculation (EGR) and air dilution is experimentally investigated, together with a zero-dimension (0-D) thermodynamic analysis. The experimental result shows that 15% gross indicated thermal efficiency (ITEg) improvement can be achieved through both air dilution and EGR dilution. Air dilution under fixed intake pressure shows significant effects on ITEg improvements. EGR dilution under fixed equivalence ratio (Phi) slightly reduces the ITEg. Further study with fixed the total charge heat capacity reveals that at lean conditions, the total charge heat capacity has greater influence on the combustion processes and ITEg than equivalence ratio. Comparing the experimental results with the thermodynamic modelling results, it indicates that combustion efficiency is an important factor that determines the ITEg with air/EGR dilution. Further analysis reveals that air dilution greatly improves the CO oxidation owing to the increased oxygen concentration, which obviously improves the combustion efficiency and ITEg.