INFLUENCE OF TRACE 2-ETHYLHEXYL NITRATE (EHN) ADDITIVES ON MACRO SPRAY CHARACTERISTICS OF HIGH-PRESSURE DIRECT-INJECTION METHANOL FUEL

This study examines the influence of trace 2-ethylhexyl nitrate (EHN) additives on the macroscopic spray characteristics of high-pressure, direct-injection methanol fuel (M100). Utilizing a schlieren visualization system coupled with high-speed imaging, we analyzed key spray parameters, including spray cone angle, spray tip penetration, and spray morphology, under varying injection pressures at both room and high temperatures. The methanol fuels tested included M100 (100% methanol) and M99 (99% methanol with 1% EHN by volume). Results reveal that the addition of 1% EHN significantly enhances spray diffusion, particularly at elevated temperatures, leading to larger spray cone angles and improved fuel-air mixing. At room temperature, injection pressures between 80 MPa and 120 MPa increased the spray cone angle of M99 by 2.17% to 3.03% compared to M100, with a corresponding enhancement of 2.21% in spray tip penetration. At higher temperatures, the spray cone angle of M99 increased by 3.66% to 12.13%, although spray tip penetration was reduced by 0.47% to 3.00%. Furthermore, the thermal decomposition of EHN promoted radial spray diffusion, resulting in a wider spray structure and broader lean mixture region, while mitigating the formation of rich mixture zones. M99 also demonstrated superior spray volume at high temperatures, with gas-phase spray cone angles 19.95%, 5.87%, and 24.49% higher than those of M100 at injection pressures of 80 MPa, 100 MPa, and 120 MPa, respectively. These findings highlight the potential of EHN additives to optimize methanol spray dynamics, enhance combustion efficiency, and reduce emissions, providing valuable guidance for methanol engine development under the dual-carbon strategy.