Numerical study on exergy losses of iso-octane constant-volume combustion with water addition

A numerical study on exergy losses in the iso-octane auto-ignition processes with water addition was conducted in an adiabatic constant-volume system. Detailed chemical mechanism of iso-octane was used in the chemical kinetic simulation, under variable initial temperatures, equivalence ratios and water to fuel ratios. The cooling, dilution, thermal and chemical effects of water addition on the exergy losses in four reaction stages, defined as the fuel-series reaction stage, the fuel fragment reaction stage, the H2O2 loop reaction stage and the H-2-O-2 reaction stage were analyzed, respectively. The cooling effect was the most influential factor, which increased the exergy losses from the first to third reaction stages, but the increase magnitude was reduced at higher initial temperatures. The dilution effect increased the exergy losses in all the four reaction stages. The thermal effect also increased the exergy losses of the four reaction stages due to the decrease of temperature. However, its influence could be almost negligible compared to the other three effects. The chemical effect decreased the exergy losses in the fuel fragment reaction stage at both low and high initial temperatures. On the other hand, the exergy losses caused by the incomplete combustion products and combustion intermediates were decreased by the cooling, dilution and thermal effects while increased by the chemical effect of water addition. In general, the four effects on the exergy losses from incomplete combustion products and combustion intermediates were greater than those on the exergy losses from chemical reactions, therefore the total exergy losses in the isooctane auto-ignition processes exhibited a declination trend with water addition, e.g. a decrease by 5% at a higher initial temperature.