Numerical Study of the Combustion Characteristics in a Syngas-diesel Dual-fuel Engine under Lean Condition

The aim of this study was to investigate the combustion characteristics of a syngas-diesel dual fuel engine operates in very lean fuel-air mixture conditions. 3D CFD simulation combined with chemical kinetics were used for analysis. The main parameter for this study was the hydrogen content in the syngas. To simulate the combustion for the dual fuel engine, a new dual-fuel chemical kinetics set was used that was constituted by merging the two chemical kinetics sets: n-heptane (173 species), and Gri-mech 3.0 (53 species) for natural gas. The calculation results were in good agreements with the experimental results. Most of the diesel fuel burned as premixed combustion mode. When the hydrogen concentration was high, as in syngas45, most of the syngas in the piston bowl and squish region, except near the cylinder wall, was combusted in the vicinity of TDC; but when hydrogen concentration was low, as in syngas25, flame propagation to the central region of the piston was delayed, which led to an increase of time loss and unburned syngas emission. Due to the strong reverse squish flow, the syngas composition did not affect the flame arrival time at the cylinder wall through the squish area by much.