Combustion Characteristics of Ammonia/Hydrogen/Butane Mixtures with Methane-Equivalent Calorific Value at Elevated Temperatures and Pressures

Abstract

Fuel mixtures with methane-equivalent calorific value (MECV) offer superior compatibility with conventional gas fuel combustion systems. This study integrates the spherical flame expansion method with both experimental and numerical simulations to record the combustion characteristics of premixed gas at Pu of 0.1-0.3 MPa and Tu of 298-448 K. The intrinsic flame instability is analyzed simultaneously using linear stability theory. The findings indicate that elevating Tu to 448 K results in a 60% increase in peak laminar burning velocity (LBV), while increasing Pu to 0.3 MPa causes a 40% reduction in peak LBV. Under different initial conditions, the LBV of mixed fuels with MECV can reach the methane level. The change in flame thickness (δ1) is opposite to the variation in Tu and Pu; the expansion ratio (σ) and the effective Lewis number (Leeff) are more easily affected by Tu. The cellular structure that appears when Pu increases is primarily caused by hydrodynamic instability (DL). As the initial temperature Tu increases, thermal diffusion instability (TD) affects flame propagation. The flame instability of premixed fuels with MECV is primarily caused by DL, whereas pure methane is more influenced by TD. An increase in Tu and Pu reduces the critical radius of the flame, leading to the earlier formation of cellular structures on the flame surface.

Keywords: Methane-equivalent calorific value, Laminar burning velocity, Linear stability theory, Butane