Numerical simulation of the combined effects of natural gas composition and pilot diesel fuel injection pressure on the dual-fuel combustion of a natural gas-air mixture under constant-volume conditions. Mbarawa, M. Journal of the Energy Institute, March 2

The objective of this work is to investigate numerically the combined effect of natural gas (NG) composition and pilot diesel fuel injection pressure on the dual-fuel (DF) combustion of the NG-air mixture under constant-volume conditions. A three-dimensional (3D) model incorporating the interaction between the fuels during combustion was used. The simulations were carried out on mixtures of four different NG (NG 1, NG 2, NG 3, and NG 4) compositions with air ignited by the pilot diesel spray injected at the different injection pressure (20, 30, 60, 90 and 120 MPa) and on combined optima for these parameters. Parameters such as combustion pressure, temperature and fuel mass concentrations with respect to time were analysed. The numerical model gives combustion pressure traces, which are similar to those from the limited experimental results from the constant-volume combustion bomb (CVCB). The predicted results show that an increase of ethane in the NG mixture leads to an increase in the NG burning. The results indicate also that higher injection pressure improves the DF combustion processes. As the injection pressure increases from 30 to 120 MPa (increases by a factor of 4) with simultaneous varying of NG from NG 1 to NG 4, the combustion pressure increases nearly by 51%. Based on the findings of this study, in order to achieve an optimal combustion process, the pilot diesel fuel spray should be injected at higher pressure while the low-level ethane concentration in the NG composition should be kept as high as possible.