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• Effects of carbon nanoparticles on the combustion of a diesel engine were studied. • Carbon nanoparticles addition into fuels markedly lowered nitrogen oxides emissions. • Carbon nanoparticles increased unburned hydrocarbon emissions at full load conditions. • Carbon nanoparticles promoted carbon monoxide formation under full load operation. • Power generation cost could be discounted by adding carbon nanoparticles into fuels. Biodiesel utilization is associated with reduced calorific value and increased nitrogen oxides emissions. Hence, various strategies are implemented to address these challenges such as water addition into diesel/biodiesel fuel blends. In line with that, this study was undertaken to explore the effect of water (3 wt.%) and aqueous carbon nanoparticles (38, 75, and 150 µM), as a novel fuel nanoadditive, on combustion and exhaust emissions of a diesel engine at a fixed engine speed of 1000 rev/min under four different engine loads ranging from 25% to 100% of full load conditions. Overall, the engine performance characteristics were improved by incorporating the aqueous carbon nanoparticles. In particular, the incorporation of carbon nanoparticles into water-emulsified biodiesel/diesel blends generally enhanced brake power and thermal efficiency while lowering specific fuel consumption. The most appealing performance features were observed for the emulsified fuel blend containing 38 µM carbon nanoparticles which increased brake power and brake thermal efficiency by 1.07 kW and 11.58% at full load operation, respectively, while it led to decreased brake specific fuel consumption by about 107.3 g/kWh. The addition of carbon nanoparticles to the water-emulsified fuel blends adversely affected unburned hydrocarbons and carbon monoxide emissions at full load conditions owing to an increase in carbon content of the fuel blends but it lowered nitrogen oxides emissions. The addition of water deteriorated the economic features of the fuel blend (i.e., the cost per kWh of power generated). However, carbon nanoparticles addition into the water-emulsified fuel blend partially neutralized the adverse economic effects of water due to its positive impacts on thermal efficiency. Overall, water-emulsified diesel/biodiesel containing 38 µM carbon nanoparticles could be regarded as the most promising emulsion fuel in terms of engine performance characteristics, nitrogen oxides emissions, as well as fuel economy. [ABSTRACT FROM AUTHOR]

Highlights • Effects of various diesel/biodiesel additives comprehensively reviewed & discussed. • Effect of engine operating factors on regulated and nonregulated emissions reviewed. • Research works related to life cycle assessment of biodiesel was reviewed. Abstract Biodiesel, in its neat or blended form with petrodiesel, is widely accepted alternative fuel for diesel engines. Although biodiesel is presumably associated with lower CO 2 , HC, and PMs emissions, it suffers from its own drawbacks including higher viscosity, lower volatility, lower heating value, and higher NO x emissions. In order to address these shortcomings and to meet stringent emission norms, diesel/biodiesel additives have attracted more attention recently owing to their ability to improve engine performance and mitigate hazardous emissions. While discrete emissions analysis could provide useful information on environmental impacts associated with various fuel additives, decision-making on such basis would be very difficult or even impossible since different fuel additives may have different positive/negative effects on pollutants generated during combustion process. This issue becomes even more serious in multi-objective optimization studies due to the fact that considering all emission indices for finding a global optimal point would be very complex as a result of conflicting objectives. Moreover, exhaust gas emission analysis does not consider environmental impacts caused in fuel production process. Discrete emissions analysis also lacks weighting in decision-making procedure since the level and degree of harmfulness of pollutants may not be comparable. Life cycle assessment (LCA) has been recognized as a valuable tool to address these challenges through systematical evaluation of potential environmental impacts of fuel additives. Accordingly, this paper was aimed at comprehensively reviewing and mechanistically discussing the effects of various diesel/biodiesel additives including metal-based, oxygenated, antioxidant, cold flow improver, lubricity improver, and cetane number improver additives as well as engine operating parameters like engine load, engine speed, EGR, and injection timing on both regulated and non-regulated emissions. Moreover, the environmental impacts of various diesel/biodiesel additives by incorporating an LCA approach was also critically discussed. [ABSTRACT FROM AUTHOR]

• Doping diesel/biodiesel emulsion fuels with CNP was environmentally studied. • Electricity use was main environmental hotspot in carbon nanoparticles production. • CNP addition led to lowest weighted environmental impacts per GJ shaft work. • Emulsion fuels doped with 150 µM CNP were the most eco-friendly at low engine loads. • Emulsion fuels doped with 38 µM CNP were the most eco-friendly at full engine loads. This study was aimed at consolidating emission indices of a diesel engine powered by carbon nanoparticles (CNP)-doped diesel/biodiesel emulsion fuels using a life cycle assessment (LCA) framework. The effects of fuel chemistry and engine load on the consolidated LCA-based environmental indicators of the engine (i.e., human health, ecosystem quality, climate change, and resource consumption damage categories) were investigated. Mineral diesel was reconstituted by adding 5 wt% biodiesel, 3 wt% water, and various concentrations of the waste-derived aqueous CNP ranging from 38 to 150 μM. Three CNP-free baseline fuels were also used as control. The engine was loaded in the range of 25–100% and at a fixed speed of 1000 rpm. In general, electricity use in the CNP manufacturing process increased all the investigated damage categories for the fuel blends dosed with the nanoadditive. Nevertheless, the lowest weighted environmental impacts per GJ shaft work were also obtained for the CNP-doped emulsified fuels. More specifically, dosing diesel/biodiesel emulsion fuel with 38 and 150 µM CNP favorably mitigated all the LCA-based environmental indicators considered herein through declining brake specific fuel consumption, boosting brake power, as well as abating lower brake specific nitrogen oxides and brake specific carbon dioxide. The weighted environmental impacts showed that diesel/biodiesel emulsion fuels doped with 150 and 38 µM nanoadditive were the most appealing fuel blends at low and full load operations, respectively. The eco-friendliest blend was diesel/biodiesel emulsion doped with 38 µM nanoadditive with an overall score of 61.3 mPts/GJ shaft work. [ABSTRACT FROM AUTHOR]