Luminosity and Thermal Energy Measurement and Comparison of a Dielectric Barrier Discharge in an Optical Pressure-Based Calorimeter at Engine Relevant Conditions

The amount of the thermal energy released in a gas mixture is crucial to characterize the igniter capability to start a robust ignition in internal combustion engines, especially in challenging operating conditions as high EGR dilution or very lean mixture. Nevertheless, the thermal energy measurement can be performed only in controlled environments, such as constant volume vessels, while it is not feasible in metal engines. This work proposes to find a correlation between the released thermal energy and the luminosity generated by the same discharge event in an optical vessel. This correlation implies that energy information could be indirectly obtained through feasible optical measurements in optical engines, and even in metal engines via low-cost diagnostic tools such as borescopes. The experimental campaign is carried out with a non-equilibrium plasma igniter, a dielectric-barrier discharge igniter (BDI). This choice is due to the inherent igniter features (i.e., the development of a volumetric discharge and the capability to modulate the discharge intensity) that makes it suitable for the purpose of the proposed campaign. Pure nitrogen, at engine-relevant pressure, is used as medium inside the vessel. The electrode voltage is varied from inception to the highest value allowed; a sweep of discharge duration is performed as well.