Visualization study on lean combustion characteristics of the premixed methanol by the jet ignition of an ignition chamber

Abstract

As an important low-carbon fuel, methanol has great potential in reducing CO2 emissions and low-temperature combustion. Meanwhile, the lean operation of methanol can reduce fuel consumption and NOx emission. However, with high latent heat of vaporization, the methanol was not easy to be ignited, especial for lean conditions. To improve the ignition energy and burning quality of the lean premixed methanol, the ignition chamber was used to produce jet flow to enhance the ignition and improve flame propagation speed under the condition of lean premixed methanol. Moreover, methanol is used in both ignition chamber and main chamber. Visualization experiment was applied by shadowgraph method to investigate the jet flow, ignition, flame propagation, and burning processes. To improve the lean burning quality of the premixed methanol, the channel diameter between the ignition chamber and main chamber, and equivalent ratio in the main chamber were selected to study the ignition and combustion characteristics. The ultra-lean premixed methanol combustion was also investigated. With a proper channel diameter, the jet flow speed was quicken with a decreased channel diameter or with lean premixed methanol. The peak pressure and pressure rise in the main chamber were also decreased with a lower equivalent ratio due to the slow jet ignition flame propagation speed under the lean mixture. For the exploratory research of the lean flammability limit of the premixed methanol (ϕ = 0.5–0.35), the ignition delay was changed so long that a misfire phenomenon was found under the equivalent ratio of 0.4, and the equivalent ratio of 0.45 was found to be proper for lean burning limit of the premixed methanol.