Thermal Energy and Luminosity Characterization of an Advanced Ignition System Using a Non-Intrusive Methodology in an Optically Accessible Calorimeter

To restrain the environmental impact of modern SI engines, igniters must guarantee stable combustions with low cycle-to-cycle variability in extreme operating conditions (high EGR, ultra-lean), via high energy release in the combustion chamber. The direct measurement of this energy is not trivial and requires a controlled environment. Luminosity detection is a non-intrusive diagnostic technique to indirectly measure the thermal energy released by the discharge on optically accessible apparatus. This work compares energy and luminosity produced by a plasma igniter in a constant volume vessel at realistic working conditions (ignition at 8 bar and air as a medium). A calibration factor can be defined to describe the thermal energy behavior as a function of the discharge luminosity and to give an assessment of such approach for its use in optically accessible engine. This study shows that thermal energy and luminosity are influenced by the gas type and related by a linear relationship for both air and nitrogen. The presence of oxygen resulted in discharges with reduced energy delivery to the medium and a lower discharge luminosity compared to nitrogen. This work outcome could improve the use of a non-intrusive methodology, based on luminosity detection, to characterize the igniter performance, exploitable for 3D-CFD.