New 0-D methodology for predicting NO formation under continuously varying temperature and mixture composition conditions

• Low cost methodology based on temperature, oxygen excess, pressure and reaction rates.
• Methodology predicts NO formation reasonably accurate in the diesel spray context.
• Considering the transport of NO into the flame core is vital to predict accurately.
• Methodology takes into account not only the NO formation but also dilution process.
• NOx sub-mechanism in GRI-Mech 3.0 behaves as pseudo-1st order reversible reaction.

The development of new diesel combustion modes characterized by low combustion temperatures, to minimize the NOx emissions, has caused a noticeable change in the diesel spray’s structure and in the NOx chemistry, gaining relevance the N2O and the prompt routes in detriment of the thermal mechanism. Therefore, to accurately predict the NOx emissions, the detailed chemistry and physics must be taken into account, with the consequence of increasing the computational cost.The authors propose in the current study a new predictive methodology associated to low computational cost, where detailed chemistry and simplified physics are considered. To diminish even more the computational cost, the chemistry was tabulated as a function of temperature and oxygen excess mass fraction (parameter which effectively couples the equivalence ratio and the EGR rate). This tool has been developed with the objective of being applicable in continuously varying temperature and mixture fraction conditions (the diffusion diesel spray context) and was validated with the Two-Stage Lagrangian model (TSL-model) and with real engine measurements.The results in both validation scenarios reflect a high degree of accuracy making it applicable, at least, to perform qualitative predictions. By extension, it is expected to perform similarly in continuously varying temperature conditions (i.e.: homogenous charge compression ignition diesel combustion modes) which are less demanding computationally speaking.