The flash points and thermal behaviors of diesel blends with biodiesels, α-pinene, d-limonene and caffeic acid as antioxidants

The present study assessed the effects of antioxidants on the flash point and thermal behavior of diesel fuel blended with 3–10 vol% biodiesel made from spent coffee grounds oil (SCGO) or Jatropha seed oil (JSO) extracted using with n-hexane or acetone, with or without α-pinene and d-limonene (as volatile antioxidants) or caffeic acid (as a non-volatile antioxidant). Effects were evaluated by assessing flash points and by thermogravimetry/differential thermogravimetry and differential thermal analysis (DTA). The flash points of the JSO and SCGO biodiesels obtained from oils extracted using n-hexane were higher than those extracted using acetone, and the addition of 10 vol% JSO or SCGO biodiesel made using acetone extraction increased the flash point by up to 2 °C. The DTA results for JSO and SCGO biodiesels also changed according to the extraction solvent. The flash points of diesel/α-pinene/d-limonene mixtures decreased as the amount of α-pinene was increased up to 10 vol%. TG peaks obtained from 10% α-pinene/d-limonene (50 vol%/50 vol%) in diesel were lowered by approximately 20 °C. The addition of 100–1000 mg kg⁻¹ caffeic acid to diesel lowered the flash point by 2 °C and shifted the TG peak to approximately 75 °C from the value of 66 °C for pure diesel. This effect was constant regardless of the caffeic acid content, while DTA results were largely unaffected by this additive. The results of this work confirm that both flash point and thermal behavior are dependent on the particular type of antioxidant employed.