Jatropha is a promising ecological fuel source for diesel engines owing to its benefits, including sustainability, accessibility, and reasonable price. Nevertheless, some disadvantages, like a slightly low heating value, high latent heat of vaporisation, and high viscosity, hinder its wide application in diesel engines. Thus, the current study intended to enhance the usability of Jatropha biodiesel in diesel engines by using multiwalled carbon nanotubes (MWCNTs) with four dosages of 25, 50, 75, and 100 mg/L added with a blend of 80 Jatropha biodiesel and 20 n-heptanol (JH). The peak cylinder pressure and heat release rate for the JH blend were reduced by 3 for both. At the same time, they were boosted by 4 for both due to the addition of MWCNTs to the JH blend. The brake thermal efficiency (BTE) was reduced by 5 for the JH blend compared with diesel, while the brake specific fuel consumption (BSFC) was raised by 4. The BTE and BSFC were enhanced by 4 for JH-MWCNT blends compared with the JH. The NOx, smoke opacity, CO, and UHC were diminished on average by 25, 40, 30, and 15, correspondingly, for the JH blend associated with diesel. © 2023 Informa UK Limited, trading as Taylor & Francis Group.