Autoignition characteristics of hydrogen-methanol blends in a rapid compression machine

Hydrogen and methanol have emerged as candidates for achieving global net zero, given their zero-carbon and single-carbon status, respectively. However, their ignition characteristics, including ignition delay times (IDTs) and Deflagration-to-Detonation Transition (DDT) behaviour, are yet to be studied. Therefore, for the first time, this study evaluated the ignition characteristics of hydrogen-methanol blends (H0-H100) using an optical Rapid Compression Machine (RCM) over a limited range of temperatures (914–981 K) and equivalence ratios (0.4–1.2), at a fixed pressure of 2 MPa. Results showed that pure hydrogen (H100) is slower to ignite than methanol (H0) across all experimental conditions examined, with its IDT 5 times longer than those recorded for H0 at 931 K, 2 MPa, and ϕ = 0.9. However, once ignition is initiated, its combustion process is >2 times faster. In addition, the IDTs along with the computed excitation times were used to map various ignition regimes on Bradley’s ξ-ε detonation peninsula framework to assess the blends’ DDT propensity. At the entrance of the detonation peninsula lies H0 and H10, while H100 advances far into the upper limit of the detonation peninsula. H100 transitions into the detonation peninsula at 3.0 MPa, which is 2 times lower than the pressure required for H0 (6.9 MPa) to transition into a developing detonation peninsula. Finally, sensitivity analysis reveals that increasing hydrogen concentration increases the magnitude of the reaction 2HO2 ↔ H2O2 + O2, thereby inhibiting reactivity and elongating IDTs in hydrogen-enriched blends.