Experimental Study on the Unstretched Laminar Flame Speed and Markstein Length of Premixed Methanol/Air Flames at Different Initial Temperatures and Pressures

Abstract

The influence of initial temperature and initial pressure on stretched and unstretched flame speed has been investigated experimentally for premixed methanol/air mixtures in a constant volume chamber with centrally ignited. The experiments were conducted at different initial temperatures (348 K, 373 K, and 398 K), initial pressures (0.5 bar, 1 bar, and 1.5 bar), and three equivalence ratios (0.8, 1, and 1.3). The results indicated that for any stoichiometry the initial temperature directly affects the stretched and the unstretched flame speed, while the initial pressure inversely affects them, and their values are peaked on the rich mixture side (Ø=1.3). By elevating the initial temperature from 348K to 398K the increment value of unstretched flame speed (S_l) was about 8.3% at stoichiometry while rising the combustible mixture pressure from 0.5 bar to 1.5 bar led to decrease S_l by 15.55%. It is also noticed that Markstein length decreases with increasing both initial temperature and initial pressure, which denotes that the instability of the flame increases with increasing these parameters.