Emission Performance of Cocoa Mucilage Bioethanol (E5) in a Legacy Spark-Ignition Vehicle Without Catalytic Converter: A Technical Case Study

This study presents a technical case study aimed at evaluating the emission performance and regulatory compliance of a low-level ethanol–gasoline blend (E5) produced from cocoa mucilage, applied in a spark-ignition vehicle applied in a spark-ignition vehicle without a catalytic converter, evaluated as a technical case study representative of aging fleet conditions. A controlled within-vehicle experimental design was employed to compare three fuels: Extra gasoline, Super gasoline, and an E5 blend (95% gasoline–5% bioethanol). Exhaust emissions carbon monoxide (CO), hydrocarbons (HC), carbon dioxide (CO2), oxygen (O2), and excess air ratio (λ) were quantified under standardized operating conditions (700 and 2500 rpm), following the Ecuadorian standard NTE INEN 2204:2017. Results demonstrate that the E5 blend improves combustion efficiency, reducing CO and HC emissions while increasing CO2, indicating enhanced carbon oxidation. A systematic shift toward leaner combustion conditions (higher λ and O2) was also observed, associated with the oxygenated nature of ethanol and improved air–fuel mixture homogeneity. However, regulatory assessment revealed only partial compliance, as all fuels met CO limits but exceeded thresholds for HC, λ, and O2. Quantitatively, the E5 blend reduced CO emissions by approximately 10–15% compared to Extra gasoline and decreased HC emissions by approximately 15–25%, depending on the operating condition. Additionally, CO2 emissions showed a slight increase, indicating improved combustion efficiency, while λ and O2 values reflected a shift toward leaner combustion conditions. Overall, the findings highlight the dominant influence of vehicle mechanical condition on emission performance.