The effect of water on the explosion characteristics of pure and diluted light alcohols

Light alcohols (methanol, ethanol, 1-propanol and 2-propanol) and their water-diluted mixtures were studied in a 20 L spherical explosion vessel at 323.15 K and 1 bar to quantify explosion parameters: explosion pressure (P_ex), maximum pressure rise rate ((dP/dt)_max) and explosion delay time (t_del). Pure samples at an equivalence ratio ϕ = 0.3 yielded P_ex = 6.88 bar and (dP/dt)_max = 365.29 bar/s for methanol, and P_ex = 6.70 bar with (dP/dt)_max ≈ 260.05 bar/s for ethanol (t_del ≈ 79 ms).

Addition of 10 vol% water to ϕ = 0.3 samples reduced P_ex by only 5–10 % but increased (dP/dt)_max by up to 15 % and shortened t_del by ≈ 20 ms, indicating enhanced flame propagation due to improved mixing. In contrast, water contents of 40–60 vol% caused P_ex to drop by 50–70 % (e.g., ϕ = 0.3 methanol P_ex < 1 bar at 40 % H₂O) and (dP/dt)_max to decrease by 60–80 %, while t_del increased by up to 50 %, reflecting strong thermal dilution and kinetic inhibition.

Comparative analysis across alcohols showed that methanol mixtures consistently exhibit the highest P_ex and (dP/dt)_max at low water dilution, followed by ethanol and propanol isomers, with 1-propanol and 2-propanol displaying similar trends but slightly lower reactivity (peak P_ex differences ≤10 %). These quantitative findings provide clear design guidelines: moderate water addition (10–30 vol%) can enhance safety without severe performance penalties, whereas high dilution (>40 vol%) effectively inertizes light-alcohol flames, offering a robust mitigation strategy in industrial settings.