Ignition characteristics of methanol-rich renewable gasoline

Abstract

In the pursuit of renewable fuels, few options are as promising as methanol. Methanol’s unique properties, such as the absence of C–C bonds, high oxygen content, and elevated octane numbers, offer a compelling avenue as an additive for conventional and renewable gasoline fuels. Notably, methanol and e-gasoline (e.g., methanol-to-gasoline, MTG) can be sustainably derived from renewable sources, reinforcing their role in cleaner energy systems. Within the MTG framework, methanol acts as a primary feedstock, subsequently transformed into high-quality e-gasoline, demonstrating its dual functionality as both a precursor and an effective octane booster. This dual functionality positions methanol as a crucial facilitator in the transition towards more sustainable and efficient fuel alternatives. In this work, we studied the impact of methanol additions (20–40 %, by vol.) on the octane and autoignition characteristics of an MTG having Research Octane Number (RON) of 82.1. The octane ratings of methanol-rich MTG were measured using a Cooperative Fuel Research (CFR) engine, while autoignition studies were conducted using a high-pressure shock tube (HPST) and a rapid compression machine (RCM). Autoignition experiments covered a broad spectrum of temperatures (680–1370 K), pressures (10, 20, 30, and 40 bar), and varied fuel composition (φ = 0.5, 1). Results indicate that ignition delay times of MTG are significantly perturbated with methanol additions. At intermediate and low temperature (≈ < 920 K), methanol-rich MTGs exhibit a strong reactivity-inhibiting effect, with ignition delays prolonged as methanol content rises. This trend agrees well with the RON values of MTG and MTG blended with methanol. Conversely, at higher temperatures (> 920 K), methanol blending promotes reactivity, shortening the ignition delays. This reactivity-promoting effect increases with increasing methanol content. A recently developed gasoline kinetic model by the authors was employed to evaluate the influence of methanol blending on MTG reactivity. Ignition delay predictions were validated using both quaternary and multicomponent (MC) methanol-containing surrogates, with the MC surrogate providing the most accurate predictions. Lastly, temperature-based sensitivity analyses were performed to identify key reactions responsible for the reactivity- promoting and inhibiting effects of methanol blending on MTG combustion characteristics.