Analysis of an Extended Ionization Equilibrium in the Post-Flame Gases for Spark Ignited Combustion

Constant volume combustion is studied, using a zero-dimensional model, which is a wide-ranging chemical kinetic simulation that allows a closed system of gases to be described on the basis of a set of initial conditions. The model provides an engine- or reactor-like environment in which the engine simulations allow for a variable system volume and heat transfer both to and from the system. The combustion chamber is divided into two zones as burned and unburned ones, which are separated by a thin adiabatic flame front in the combustion model used in this work. A detailed chemical mechanism is applied in each zone to calculate the temperature and pressure history. Equilibrium assumptions have been adopted for the modeling of the thermal ionization, in which Saha’s equation was derived for singly ionized molecules. The investigation is focused on the thermal ionization and electron attachment of 13 chemical species by solving a set of 6 chemical reactions dynamically, the equilibrium calculation using Saha’s equation is performed in a post process, using the temperature and pressure history from the previous model. The experiments that were used for the validation of this model were performed in constant-volume bomb. The outputs generated by the model are temperature profiles, species concentration profiles, ionization degree and an electron density for each zone. The model also predicts the pressure cycle and the ion current. The results from the simulation show good agreement with the experimental measurements and literature data.