Ethanol reduces emissions but damages engines? a systematic literature review and meta-analysis of performance, emissions, and technological risks of 4-stroke motor engines

Abstract

The integration of ethanol as a fuel additive in 4-stroke internal combustion engines has garnered increasing attention as a strategy for reducing greenhouse gas emissions, particularly within the transportation sectors of developing countries. This study aims to systematically evaluate the impact of ethanol–fuel blends on exhaust emissions, engine performance, and long-term mechanical reliability. A Systematic Literature Review (SLR) combined with quantitative meta-analysis was conducted using 37 peer-reviewed publications published between 2020 and 2025. The results indicate that ethanol blending contributes significantly to emission reductions: carbon monoxide (CO) decreased by an average of 8%, hydrocarbons (HC) by 8%, nitrogen oxides (NOx) by 3.5%, and particulate matter by 22.5%. However, the lower heating value of ethanol led to an average increase in fuel consumption of 13.75%. In addition, light to moderate engine wear was observed due to elevated peak pressures and combustion temperatures, indicating potential reliability risks under long-term use. These findings suggest that while ethanol is effective in enhancing environmental performance, its implementation must be accompanied by advanced combustion control strategies and engine optimization to maintain operational durability. This study contributes a novel analytical framework that integrates environmental, performance, and mechanical risk dimensions, offering a scientific basis for future engine design and fuel policy decisions centered on bioethanol applications.