Experimental study of using additive in the pilot fuel on the performance and emission trade-offs in the diesel/CNG (methane emulated) dual-fuel combustion mode

Abstract

In this work, diesel-n-butanol blends as the pilot fuel were studied to explore the possibility of improving the performance and emissions in the dual-fuel combustion mode with CNG, and the trade-offs among NOx, THC and CO were also discussed. The pilot fuels including B0 (pure diesel), B10 (90% diesel/10% n-butanol) and B20 (80% diesel/20% n-butanol) were compared under two engine loads. The experiments were conducted by sweeping a wide pilot fuel start of injection (SOI) timings at two CNG substitution rates for each load. For 5 bar indicated mean effective pressure (IMEP), B10CNG40 (at the 40% CNG substitution rate) reveals the highest indicated thermal efficiency (ITE) and lowest THC emissions. While it results in slightly higher NOx emission. B20CNG70 can significantly reduce the NOx emission due to better homogeneity and higher evaporation latent heat of n-butanol. The obvious trade-offs between NOx and THC, NOx and CO can be observed at the retarded pilot fuel SOI timings. For 7.5 bar IMEP, B10CNG60 and B20CNG60 can improve ITE and lower the THC emissions, while maintaining the equivalent level of NOx emission relative to the cases at the 80% CNG substitution rate. Adding n-butanol leads to the trade-off between THC and CO emissions.