This paper focuses on the scalar flux modelling in the predictions of turbulent jet diffusion flames. Recently, full non-linear second-moment closure modelling approach (model which include non-linear effects for pressure-strain and pressure-scalar correlations), that guarantee realizability constraint and a two-component limit, has been applied for diffusion flames. It has been demonstrated to be particularly beneficial for flame predictions especially on the prediction of scalar transport. Systematic tests are being carried out to assess its advantages and disadvantages over other simpler models. Two methane jet flames have been chosen for the current study.