Cycle Resolved In-Cylinder NOx and Ion Current Measurements in a Diesel Engine

This paper investigates the relationship between NO_x and ion current measured inside the combustion chamber of a heavy duty diesel engine under different operating conditions. Nevertheless, ion current is a local signal, thus it is important to measure NO_x concentrations at the same exact location of the ion current probe. A novel technique is developed to simultaneously sample in-cylinder NO_x and measure the ion current signal by adapting gas sampling probes for ion sensing. The cycle-resolved traces for the rate of heat release, NO mole fraction and ion current were analyzed to determine the contribution of the premixed combustion and the mixing-diffusion controlled combustion on NO formation and ionization in diesel engines.