Polydispersity Effects in Low-order Ignition Modeling of Jet Fuel Sprays

ABSTRACT

Low-order ignition models are important tools in the design of aviation gas turbines. In this paper, a stochastic model that predicts the ignition probability in a combustor based on a time-averaged cold-flow solution is extended to include local fuel concentration fluctuations due to the polydisperse nature of the spray. For this, a stochastic approach to modeling such fluctuations is considered, and the effects of the flow and mixture parameters on the resulting equivalence ratio pdfs are investigated. The concentration of fuel in large droplets results in a high variation of the local equivalence ratio, hence affecting the local flammability factor at the model’s cell scale. The extinction criterion of the ignition model based on a critical Karlovitz number is calibrated based on ignition probability data from canonical experiments using jet fuel, suggesting critical Karlovitz values of spray flames between 0.2 and 0.6, which is to be contrasted with values of 1.5 for gaseous fuels.

KEYWORDS:

• Forced ignition
• low-order modeling
• jet fuel
• polydisperse sprays

Acknowledgments

P.M. de Oliveira gratefully acknowledges the financial support of the Brazilian Space Agency and Brazil’s National Council for Scientific and Technological Development. M.P. Sitte is grateful for the financial support from the Gates Cambridge Trust. The authors also kindly acknowledge the funding granted by the European Commission Clean Sky 2 project PROTEUS (785349).