Combustion, Performance, and Emission Characteristics of Honge (Pongamia pinnata) Biodiesel Enriched with Carbon Nanotube-Based Nano-Additives: A Systematic Review with Particular Emphasis on Single-Walled Carbon Nanotubes

Abstract

With the growing need for sustainable alternative fuels, biodiesel applications and nano-additives to optimize the performance of CI engines were the topics of interest. In the present study, a systematic review has been performed and the implications of combustion parameters, performance and exhaust emission reduction with the use of Honge (Pongamia pinnata) biodiesel and carbon based nano-additives in the CI engine with primary reference to SWCNTs (single walled carbon nanotubes) have been discussed. This involved a systematic literature review in the main electronic databases, reported, following PRISMA 2020 guidelines. Eleven experimental studies were published in the last seven years (2008-2025) and fulfilled the eligibility criteria and therefore were included in this study for qualitative synthesis. Moderate Honge biodiesel blends (B20 – B40) show to be the best compromise in terms of engine performance and the emission characteristics. Typically these blended results demonstrated decreases in carbon monoxide (CO), hydrocarbon (HC), smoke opacity, and particulate matter (PM) while increases in biodiesel content were correlated with an increase in brake-specific fuel consumption (BSFC). Further, the combustion efficiency has been improved by the addition of these carbon based nano-additives such as carbon nanotubes (CNTs), multi-walled carbon nanotubes (MWCNTs), graphene, and SWCNTs, which enhanced fuel atomization, heat transfer, combustion oxidation reactions, brake thermal efficiency (BTE), compression ignition response, and heat release rate. Several drawbacks persisted, however, with higher nitrogen oxide emissions (NOₓ). There was less evidence that addresses specifically SWCNT-enhanced biodiesel with only one eligible study considered for this. The present study confirms that the nano-enhanced Honge biodiesel fuel has a good potential for a sustainable fuel in CI engines, in general. More detailed, standardised research should be undertaken to achieve the best dosage of nanoparticles, determine the durability of the engine over longer periods and to enable the development of suitable NOₓ mitigation measures for application.