Numerical simulation study on NO generation characteristics of methane/n-heptane dual fuel counterflow flames under different pressures

Abstract

This paper presents a numerical study of counterflow methane/n-heptane dual fuel flames, investigating the influence of pressure on flame structure and NO generation characteristics. The results demonstrate that, as pressure increases, the peak temperature and heat release rate of the flame increase, while the NO emission index decreases. The prompt NO emission index experiences a monotonic reduction as pressure increases, while the thermal NO emission index initially increases and then decreases. NO emission index via reburn route displays non-monotonicity with increasing pressure. Elevated pressure induces a decline in the mole fraction of radicals (CH, CH2 and HCCO) crucial for prompt NO formation, consequently suppressing the formation of prompt NO. The principal reaction responsible for the consumption of reburn NO at lower pressures is HCCO+NOCO+HCNO, whereas the primary reaction for generating reburn NO is H+HNOH2+NO. However, at higher pressures, the reaction H+HNOH2+NO takes precedence as the dominant reaction consuming NO.