Influence of antioxidants on fuel stability of Calophyllum inophyllum biodiesel and RSM-based optimization of engine characteristics at varying injection timing and compression ratio

‘Fuel stability’ is one of the most significant properties of biodiesel, which insists the biodiesel stability during prolonged storage period. This paper investigates the effects of commercially available and cheap synthetic antioxidants (PY—pyrogallol, PG—propyl gallate, TBHQ—tert-butylhydroxyquinone, BHT—butylated hydroxytoluene, BHA—butylated hydroxyanisole) on the accelerated oxidation stability, storage stability and thermal stability of Calophyllum inophyllum biodiesel. Characterization of biodiesel oxidation variability regarding different antioxidants was evaluated using Fourier Transform Infra-red (FTIR) spectroscopy by analyzing the FTIR spectrum regions of C–H bonds of the respective antioxidants/biodiesel blends. TBHQ dosed with pure biodiesel (B20D3) enhances the thermal stability by 12.05%, storage stability by 8.13% and oxidation stability by 25.27%, when compared to those of biodiesel blend (B20) without any antioxidant. The order of effectiveness of antioxidants at constant 1000 ppm concentration with pure biodiesel is obtained as TBHQ > PG > PY > BHT > BHA. B20D3 has been evaluated for the combined effects of varying injection timing (IT) (21°–24° BTDC) and compression ratio (CR) (16.5:1–18:1) on engine characteristics through experimental investigation and response surface methodology optimization. CR of 17.5 and IT of 23° BTDC were found to be optimal values for superior performance and lower emissions with composite desirability of 0.785.