**1. Introduction**

The amount of CO2 in the atmosphere has increased significantly since the start of the industrial era in the 18th century [1]. Fossil fuels used in the transportation and electricity (and heat) production sectors are responsible for about 40% of the total global greenhouse gas (GHG) emissions [2]. In the UK, road transports are responsible for 22% of the total UK CO2 emissions [3]. Use of renewable biofuels instead of fossil based fuels could reduce the GHG emissions significantly [4–6]. Biodiesels, produced through transesterification of seed oils (or wastes), have diesel like physico-chemical fuel properties and may substitute fossil based diesel fuel. They are biodegradable, has higher oxygen content and cetane number [7]. Engine performance and combustion characteristics were assessed by researchers using various biodiesels and their blends with fossil diesel [8,9]. The type of feedstock used for biodiesels production affect life cycle energy and GHG emission of the transesterification process. Hence, it is important what type of crops are used for biodiesel production such as edibles

and non-edibles. This has led to controversy surrounding farmland and whether it should be used for food or fuel [6]. Mofijur et al. [10] studied the engine performance characteristics operated separately with biofuels obtained from edible and non-edible feedstocks. Two biodiesels, produced from palm (edible) and jatropha (non-edible) oils were used. They found that considering the overall emission reduction potential, jatropha biodiesel was better than palm biodiesel [10,11].

The effects of various oxygenated additives on biofuels were investigated by the researchers to further improve the combustion and emission characteristics of the biofuels powered internal combustion (IC) engines. For example, nanoparticles were added to fuel mixtures to improve the engine performance and combustion characteristics; typically, metallic oxides nanoparticles were used to increase the heat release rate and thermal efficiency [12–14]. Metal-oxide nanoparticles have the ability to donate oxygen atoms to the fuel mixture and can create high surface to volume ratio; hence, they act as high reactive medium for combustion. Other advantages of adding nanoparticle additives are: increased thermal conductivity, flash point and fire point temperatures; and reduced kinematic viscosity [12,13]. The nanoparticle additives essentially behave like a catalyst. Due to high surface to volume ratio they are able to react more effectively, thus increasing the rate of fuel combusted [14,15]. Cerium oxide, aluminium oxide, cobalt oxide and zinc oxide are amongst the most popular nanoadditives due to their unique composition that aids in a more effective way of burning the fuel inside the engine cylinder [16–18]. Effective mixing of nanoparticles in the fuel mixture is important, literature reported that use of surfactant and ultrasonic machine helped to produce single phase nanoparticle fuel blend [19,20].

Furthermore, studies demonstrated that addition of cerium oxide in the fuel has the ability to reduce in-cylinder pressure, this in turn causes a decrease in the NOx emissions; in addition, due to the catalytic soot combustion characteristics, cerium oxide has the added capacity to remove soot from the particulate filter [11,21]. Razek et al. [22] investigated the effects of nanoparticle additives on jatropha biodiesel (JBD)-diesel blends. They reported that blend containing 20% JBD and 80% diesel with Al2O3 nanoadditives gave 12% increase in brake thermal efficiency (BTE) and 12.5% reduction in brake specific fuel consumption (BSFC). The authors reported that NOx emission was decreased by 13%; emissions of unburnt hydrocarbon (UHC) and CO gases were reduced by 10% and 29% respectively [22]. Effects of nanoadditives on waste-derived biodiesels were also investigated. A significant reduction in CO, UHC and NOx emissions were reported when poultry litter biodiesel-diesel-nanoparticle blend was used in the IC engine instead of the fuel blend without nanoparticles [23]. Compared to the fossil diesel fuel, up to 2% increase in engine power and 7.08% decrease in BSFC were observed when multi wall carbon nanotubes and nanosilver nanoparticles were added to the waste cooking oil biodiesel-diesel blends [24]. Nanoadditives enhanced the combustion characteristics of the pure fossil diesel powered engine. As a result of better combustion, the CO2 emissions increased by up to 17.03% and CO emissions decreased by 25.17% when compared to pure fossil diesel fuel operation [24]. Up to 8% reduction in BSFC was achieved when ferrofluid nanoparticles were added to pongamia biodiesel-diesel (B20) blends [25]. The authors reported that due to improved burning, the emissions of CO and UHC gases were also decreased when compared to non-additive fuel blends [25].

The thermal efficiency was improved by about 2.2% and emissions of HC, CO and smoke were considerably decreased when copper oxide nanoparticles-mahua biodiesel-fossil diesel blends were used instead of B20 blend without nanoparticles [26]. Basha et al. [27] studied the combined effects of carbon nanotubes and diethyl ether additives on biodiesel emulsion fuels. They reported that additives gave better engine performance than pure biodiesel and pure fossil diesel [27]. In another study, carbon nanotube and ethanol was added to B2 fuel (B2E4C60) and observed a 15.52% increase in engine power and 11.73% decrease in BSFC as compared to when the engine was operated with pure fossil diesel fuel [28]. The authors also found that due to the additives, the CO and UHC emissions were decreased by 5.47% and 31.72% respectively, but the NOx emissions increased by about 12.22% [28]. Approximately 7–20% and 15–28% reductions in CO and UHC gases were observed when graphene oxide nanoparticles were added to *Ailanthus altissima* biodiesel-diesel blends (B0, B10, and B20) [29]. Furthermore, the effects of nanoadditives on a thermal barrier coated engine were also investigated. A simulation study on a coated piston showed increased temperature distribution and reduced heat flux when compared to uncoated piston [30]. Due to the reduced heat flux, an improvement in thermal efficiency by 1.75% was observed on coated engine using *Cymbopogon flexuosus* biofuel-fossil diesel blends with 20 ppm cerium oxide nanoadditive when compared to an uncoated engine using the same fuel [30]. In a separate study, *Cymbopogon flexuosus* biofuel (20%)-fossil diesel (80%) blends with various proportions of cerium oxide nanoadditives achieved up to 4.76% higher thermal efficiency and 6.6% decrease in smoke opacity as compared to biofuel-diesel blends without nanoadditives [31]. Addition of nanoparticles gave increased heat release rate and peak in-cylinder pressure; emissions of UHC, CO and NOx gases were reduced by 7%, 12.5% and 3%, respectively, at full engine load. [31]. The literature reports that in a thermal barrier coated engine, the nitrogen oxides gases were increased and emissions of UHC, CO and smoke opacity were reduced. Carbon-coated aluminium additives were added in biodiesel-diesel-ethanol blends and tested in a diesel engine to assess the engine performance and emission characteristics; the study found that B10 blend with 4% ethanol and 30 ppm nanoparticles reduced both BSFC and NOx emissions by about 6% when compared to B10 fuel (without ethanol and nanoparticles) [32]. However, the authors reported that compared to B10 fuel, the particles number (PN) emissions were increased by 2.2 times for B10-ethanol-nanoparticles fuel; on the contrary, this was decreased by about 11.8% for B10-ethanol fuel [32].

Up to 12% improvement in BTE, 30% reduction in NO emission, 60% reduction in CO emission, 44% reduction in UHC emission and 38% reduction in smoke emission were observed when both cerium oxide and alumina nanoadditives was added to B20 jatropha biodiesel blend as compared to B100 fuel [33]. Ignition delay was affected when nanoadditives were used in the fuel. Jatropha biodiesel emulsion fuel (83% jatropha biodiesel, 15% water, and 2% surfactants (Span80 and Tween80)) mixed with aluminium nanoparticles gave lower ignition delay, better engine performance and reduced emissions compared to pure jatropha biodiesel or jatropha biodiesel emulsion [19]. Another study reported that the ignition delay was deceased by about 9% when carbon nanotube and Ag nanoparticles were added to jojoba biodiesel-diesel blends [34].

Jatropha oil (JCO) is derived from the *Jatropha curcas* plant, they can be grown in unfarmable lands and can endure adverse weather conditions. Non-edible oils are the most appropriate feedstock for biodiesel production as they do not put a strain on global food demand [35]. However, the concern with non-edible feed stocks is that some crops have a high Free Fatty Acid value (FFA). The FFA value determines whether or not the oil needs to undergo an additional process (ie. esterification) before transesterification. The esterification process or 'pre-treatment' makes biodiesel production a two-step process capable of producing a high yield of fuel in a relatively short amount of time [36]. *Jatropha carcus* trees are grown in many parts of India and in Africa. Use of 100% biodiesel (B100) would provide much more emission reduction benefits than using biodiesel-diesel blends. Most studies found in the literature reported effects of nanoparticles on jatropha biodiesel-diesel blends. The aim of the current study is to investigate the performance, combustion and emission characteristics of a multi-cylinder diesel engine operated with nanoparticles—100% jatropha biodiesel fuel mixture. Initial findings of the study have been presented at the 13th SDEWES conference [37]. Two nanoparticles cerium oxide and aluminium oxides will be used in this study. Jatropha biodiesel will be produced in the lab using two stages, i.e., esterification and transesterification. Nanoadditives-J100 fuel blends will be tested in a multi-cylinder engine. The specific objectives of this study are:

