The impact of graphene nano-additives on engine performance, combustion characteristics, emission behaviour, and catalytic-converter durability is investigated in a single-cylinder compression-ignition engine operated with Pongamia pinnata biodiesel blends. In controlled operating conditions, conventional and graphene-enriched (100 ppm) blends (B20, B30) are tested against mineral diesel. Fuel properties are characterized according to ASTM standards; catalytic converter degradation is studied with SEM-EDS and a deposit-based life estimation. The results show improved combustion behaviour with the incorporation of graphene, enabling biodiesel blends, especially B20Gr, to achieve performance levels near diesel, with higher brake thermal efficiency, lower fuel consumption, and comparable pressure characteristics, with moderately lower heat release intensity but still higher than that of the untreated blend. Emission analysis reveals that carbon monoxide (CO) and unburnt hydrocarbon (UHC) continuously decreased, facilitated by improved oxidation kinetics and enhanced fuel-air mixing. Furthermore, nitrogen oxides (NO x ) emissions from all fuels increase with engine load, but the addition of graphene slightly mitigates this trend compared with base biodiesel blends. The SEM-EDX analyses show significant carbon deposition in the catalyst converter, mainly in reduction zones, with stronger carbon capture for biodiesel- and graphene-doped fuels than for diesel. Life-expectancy modelling also confirms a loss in catalyst durability for biodiesel blends, and the addition of graphene results in only a marginal improvement (9500 h for diesel, 4600 h for B20, and 4840 h for B20Gr). Overall, graphene-enriched Pongamia biodiesel improves combustion and emission performance in a balanced manner but accelerates catalyst ageing, highlighting the need for advanced after-treatment strategies and thermally resilient catalyst materials for long-term, sustainable application in CI engines.
Krishnamurthy et al. (Mon,) studied this question.