Development of a Physically/Chemically Based Approach for 2-Stage Ignition Delay Calculation in Medium Speed Dual-Fuel Engines

This paper presents a newly developed 2-stage ignition delay model for pilot ignited medium speed dual-fuel (DF) engines. This provides the first major step towards a new combustion model for the prediction of the DF combustion in the context of 0D/1D simulation. The combustion models known from literature are based on empirical models of a steady jet. Here in most cases the package model of Hiroyasu is used. Because in a DF engine the injection timing of the diesel fuel is very early and the injection ends before ignition, the spray behavior differs from that of a steady jet. Especially the end-of-injection transients lead to stronger entrainment and therefore affect the ignition delay. In addition, the presence of natural gas in the cylinder extends the ignition delay at the chemical level. In this paper the 1D transient spray model of Musculus and Kattke is used to describe the spray behavior. The spray model is extended with a mixing controlled evaporation model to derive the temperature distribution inside the spray. A 2-stage ignition delay model with low temperature heat release is developed based on extensive reaction kinetic simulations with an extended n-heptane mechanism. A comparison with measurements of a single cylinder research engine shows good agreement of the model, whereby no parameter had to be adjusted, but could be taken from the literature. Moreover, a comparison of 1-stage and 2-stage ignition delay calculation shows the benefit of the outlined approach.