Numerical investigation of natural gas utilization in diesel engine

In this study, the effects of natural gas-diesel fuel (NG-DF) dual fuel applications on combustion, engine performance, fuel cost and exhaust emissions in diesel engines were investigated numerically. For this purpose, a thermodynamic based multi-zone cycle model was developed to calculate the diesel engine cycle. The reliability of the developed model for neat diesel fuel (NDF) and NG-DF dual fuel cases was checked by comparing it with experimental results and with that of numerical and experimental results proven in the literature. Then, using this model, three different methods were numerically investigated for adding natural gas (NG) to the intake air at different ratios (IADRs) in a current automobile diesel engine at 2000 rpm, full throttle and under full load. In the first application, NG was added to IADRs to provide 30.5 kW effective power produced by NDF and the injected diesel fuel (DF) was reduced. At the end of the application, it was determined that cylinder pressures, heat release rates (HRRs), NO emission decreased significantly, and specific fuel consumption (BSFC) and CO emission increased significantly. In the second application, NG was added to IADRs to provide the equivalence ratio of 0.707 which occurs for NDF and injected DF was reduced to a suitable amount. In conclusion, it was determined that cylinder pressure values, HRRs decreased, and CO, NO values decreased significantly without much deterioration in BSFC. In the third application, NG was added to the intake air at low ratios without changing amount of the injected DF. Here, it was observed that as the NG ratio increased, BSFC increased, CO emission increased significantly and whereas NO emission partially decreased. Keywords: Diesel engine, Thermodynamic based multi-zone cycle model, Dual fuel combustion, Engine characteristics, NO exhaust emission