Effects of 2-EHN Additive Fraction and Ambient Conditions on Methanol Auto-Ignition

Methanol is a promising renewable synthetic fuel for achieving carbon neutrality and has attracted attention as a future marine fuel due to its liquid phase storage capability, low sulfur emissions, and high latent heat of vaporization, which reduces nitrogen oxide emissions. However, its application in compression-ignition engines is limited by its high auto-ignition temperature. Although methanol–diesel dual-fuel combustion has been widely adopted, the use of diesel fuel prevents complete elimination of regulated emissions. As an alternative, cetane boosters have been proposed to enable fully auto-ignited methanol combustion. In this study, the auto-ignition characteristics of methanol blended with 2-Ethylhexyl nitrate (2-EHN) were experimentally investigated in a constant-volume combustion chamber. The additive volume fraction was varied from 0 to 10%, and combustion behavior was evaluated using ignition delay, lift-off length, flame visualization, and accumulated heat release rate derived from chamber pressure measurements. Increasing the 2-EHN fraction significantly shortened ignition delay and reduced lift-off length, indicating enhanced auto-ignition stability. A notable increase in accumulated heat release rate was observed above 5% additive fraction under low-temperature conditions. Ambient temperature showed a stronger influence on methanol auto-ignition than additive fraction, with saturation behavior above approximately 1150 K. These findings demonstrate the feasibility of stable auto-ignition combustion of additive blended methanol for high compression ratio compression-ignition engines.