Experimental Study on Laminar Burning Velocity and Flame Instability of Liquefied Petroleum Gas/Dimethyl Ether Blended Gas: Effects of Equivalence Ratio and Blended Ratio

ABSTRACT Liquefied petroleum gas/dimethyl ether (LPG/DME) blended gas is a promising clean alternative fuel, characterized by high efficiency and clean combustion properties. To reveal the combustion characteristic mechanism and evolutionary process under multi‐factor coupling conditions, this study investigates the propagation and instability characteristics of spherically expanding flames of LPG/DME blended gas at different equivalence ratios ( φ = 0.7–2.0) and blending ratios ( X = 0–1.0) using a constant volume combustion bomb and high‐speed schlieren technique. Combined with CHEMKIN chemical kinetic calculations (mainly including reaction pathway and sensitivity analyses), the evolution and competition laws of diffusive‐thermal and hydrodynamic instabilities under different φ and X conditions are explored, as well as the significant influence of buoyancy instability on flame morphology and propagation under highly fuel‐rich conditions. Results show that the laminar burning velocity ( S L ) first increases and then decreases with φ , with a peak value of 0.47811 m/s occurring at φ = 1.0–1.2. In contrast, S L decreases with increasing X , reaching a minimum of 0.04262 m/s. Under lean conditions, the effective Lewis number Le eff ≫ 1, and the flame remains stable under the dominant effect of diffusive‐thermal instability. Under rich conditions, increasing X enhances diffusive‐thermal instability, raises the flame thickness ( δ ) to a maximum of 0.624 mm, and decreases the thermal expansion ratio ( σ ) to a minimum of 6.595, thereby weakening hydrodynamic instability and causing flame instability. At a highly rich condition of φ = 2.0, the dominant instability mechanism shifts from the combined effect of diffusive‐thermal and hydrodynamic instabilities to buoyancy instability, further increasing the tendency toward flame instability. Through reaction path and sensitivity analysis, the mechanism that LPG addition influences combustion rate by controlling OH radical fraction is clarified.