Quantifying Environmental and Health Impacts of Conventional Diesel and Methane Diesel RCCI Engine Emissions: A Numerical Analysis

A reactivity-controlled compression ignition (RCCI) engine offers ultralow soot and nitrogen oxide (NOx) emission in addition to higher thermal efficiency than diesel or compression ignition (CI) engines. However, the higher emissions of unburned hydrocarbons (HC) and carbon monoxide (CO) from RCCI engines pose a significant challenge that hinders their adoption in the future automotive sector. Additionally, HC includes several hydrocarbons that harm human health and the environment. This study aims to minimize HC and CO formation and emissions by implementing different injection strategies, including adjustments to spray angle configuration, injection timing, and fuel premixing ratio. Additionally, the study examines how different injection strategies affect the spatial and temporal distribution of HC and CO inside the combustion chamber. To achieve this objective, a numerical investigation is conducted on a single-cylinder diesel engine modified to operate in RCCI mode, utilizing a detailed reaction mechanism with ANSYS FORTE. The reaction mechanism comprises 137 species and 1,022 reactions, using n-heptane and CH4 as fuel surrogates. Initially, the computational model is developed using engine geometry and validated against experimental results for conventional diesel and RCCI modes, after which a parametric investigation is conducted. The results demonstrate that, among injection strategies, the spray configuration has the greatest impact on HC and CO emissions. Narrow spray configuration in RCCI combustion leads to a significant decrease in HC and CO emissions. HC and CO emissions increase with advanced injection timing and a higher fuel premixing ratio. RCCI engines exhibit lower acidification potential and eutrophication potential equivalent emissions compared to conventional diesel engines.