A phenomenological model for diesel and natural gas dual-fuel combustion for low diesel percentage has been successfully developed. The spray was divided into multiple zones to account for concentration and temperature gradients and stratified entrainment of charge into the spray. Similarly, the premixed “air + NG” burnt gases as combustion progresses were divided into multizones and, hence, could predict the temperature gradients.
The combustion model has been validated on available experimental data published in literature. A full-cycle simulation was attempted to evaluate the overall performance of a dual-fuel engine in terms of indicated power at different parametric conditions. The model predictions were compared with experimental pressure time histories and observed to be closely matching. The variations of different combustion parameters such as ignition delay, indicated power, cylinder pressure, and NOx emissions were found to be comparable with published experimental results, except for very advanced timings.
With very advanced timings, the injected diesel fuel penetrates further, due to longer ignition delay, breaks up, evaporates, and disperses, leading to homogeneous charge compression ignition (HCCI) combustion leading to very low NOx emissions (<0.1 g/kWh). The dual-fuel phenomenological model with an intact spray feature is limited in capturing the physics and needs to be judiciously applied for very advanced injection timings.