Multi‐objective optimization of injection timing, pressure, and alcohol share in <scp>CRDI</scp> engines and comparative analysis of ethanol and isoamyl alcohol blends using the Taguchi <scp>GRA</scp> method

Abstract This study presents a comparative optimization of ethanol and isoamyl alcohol as oxygenated additives in cottonseed biodiesel‐diesel (B20) blends for a common‐rail direct injection (CRDI) engine. An integrated Taguchi‐Gray Relational Analysis (GRA) approach was employed to optimize three key parameters—injection timing (IT), injection pressure (IP), and alcohol share—to enhance performance and minimize emissions. The results demonstrate that an injection timing of 27°CA bTDC was optimal for minimizing emissions with both alcohols. The optimum combination for ethanol blends was a 15% share at 200 bar IP, whereas for isoamyl alcohol, a 25% share at 240 bar IP yielded the best results. Analysis of variance (ANOVA) revealed that injection timing was the most influential parameter for controlling CO, HC, and smoke emissions in ethanol blends, while the ethanol proportion significantly affected brake thermal efficiency (BTE) and brake‐specific fuel consumption (BSFC). For isoamyl alcohol blends, injection pressure was the dominant factor for BTE, and the alcohol share had the greatest impact on BSFC and NOx. The study concludes that ethanol is more effective for emission reduction, while isoamyl alcohol offers superior combustion efficiency. This work provides a novel dual‐alcohol comparison under identical CRDI conditions, offering valuable insights for implementing sustainable biodiesel‐alcohol blends.