Method for pressure trace based thermodynamic analysis of pre-chamber combustion

An effective way to ignite low-reactivity mixtures in engines is to allocate the ignition source, usually a sparkplug, inside a pre-chamber (PC); the ignition of the premixed charge in the main chamber (MC) is then accomplished by the turbulent jets exiting the PC. Due to the mass and enthalpy exchange between the two chambers, which are connected via narrow orifices, the analysis of the combustion progress in the PC and in the MC is more complex than for conventional engines, where only a single volume (the MC) needs to be considered. This article proposes a method for the thermodynamic analysis of PC combustion based on the simultaneous pressure measurements inside the two chambers. The method calculates the volume averaged PC mass and temperature, the enthalpy flow responsible for turbulent jet ignition as well as the total heat release rate in the PC. The proposed method is validated with CFD simulations of a canonical, constant volume setup and a singlecylinder pre-chamber engine, showing good agreement in the quantitative calculations of the heat release rate in the PC and the enthalpy flow between the PC and the MC. The model is then tested using experimental data originating from a 4-cylinder passenger car-sized engine operated with natural gas.