Performance and emission characteristics improvement studies on a biodiesel fuelled DICI engine using water and AlO(OH) nanoparticles

Highlights

• Biodiesel emulsions were prepared using surfactants and were tested in an engine.

• Emulsion was an efficient method to mitigate the NO level.

• Aluminium oxide hydroxide (AlO(OH)) nanoparticles were used as a fuel borne catalyst.

• Significant reduction in level of pollutants in emissions using nanoparticles.

• Characterization of AlO(OH) nanoparticles using XRD and TEM was analysed.

Abstract

The paper describes a sequence of experimental investigations conducted on a biodiesel fuelled Direct Injection Compression Ignition (DICI) engine with an objective of improving its working characteristics using Aluminium oxide hydroxide (AlO(OH)) nanoparticles as a fuel additive. Systematically prepared biodiesel from Jatropha oil and commercially available nano-sized AlO(OH) were used in this investigation. The AlO(OH) nanoparticles crystallite size and morphology were studied using XRD (X-ray diffraction) and Transmission Electron Microscope (TEM). The particles were dispersed in ppm levels (25, 50 and 100 ppm) in a set of biodiesel emulsion fuels (BD5W: Blend of 93% biodiesel + 1% Span80 + 1% Tween80 + 5% water, and BD10W: Blend of 88% biodiesel + 1% Span80 + 1% Tween80 + 10% water). The working characteristics of test fuels were investigated in a test rig, consisting of a single cylinder, four stroke DICI constant speed engine (Speed = 1500 rpm, Compression ratio = 17.5), data acquisition system and an electric loading device (Alternator). The results of the test fuels were analysed and compared with those of neat diesel and neat biodiesel. The analysis revealed that the performance parameter, namely, brake thermal efficiency, was lower, and NO level in the engine exhaust was higher for the biodiesel than that for neat diesel. However, the performance and emission characteristics were notably enhanced by the inclusion of water and nanoparticles.

Introduction

Compression ignition engines play an important role in transportation, locomotives and industrial sectors due to their simplicity of operation, high reliability, durability and well-established design. On the other hand, the release of hazardous pollutants like smoke, carbon monoxide, unburned hydrocarbons and nitrogen oxides are a great threat to mankind, flora, fauna, the ozone layer and the environment. Further, fossil fuels are being consumed rapidly, and their existence is in question for future generations. The scientific community searches intensively for various alternative sources of renewable agriculture based materials as feedstock to replace the fossil fuels of diesel engines. Under these circumstances, over the last two decades, biodiesel has emerged as a substitute for conventional fuels. It is a sulphur free, oxygenated, non-hazardous and eco-friendly fuel with a prospective of reducing exhaust emissions. In addition, biodiesel has more oxygen molecules in its molecular structure, which in turn leads to an improvement in its combustion and reduction of carbon monoxide (CO), unburned hydrocarbons (UHC) and particulate matters. On the other hand, biodiesel causes the formation of more nitrogen oxides (NO_x) due to the generation of high temperature in the combustion chamber and oxygen availability [1].

Many researchers sought to improve performance while reducing the level of pollutants in the exhaust emissions of compression ignition engines by adopting engine hardware modifications, fuel properties alteration and exhaust gas treatment techniques. Based on the literature and the experimental studies, Nabi et al. [2] conducted experiments and studied the working characteristics of diesel engines using biodiesel produced from Cottonseed oil, and the results were compared with those of neat diesel. They found that BTE was decreased for biodiesel mixtures (B10: Blend of 90% diesel + 10% biodiesel; B20, B30) due to its low heating value, high viscosity and high density. In spite of the decreased performance, they observed improved combustion characteristics due to the existence of more oxygen, which caused a reduced level of pollutants (UHC, CO and smoke) in the engine exhaust for biodiesel mixtures. Chauhan et al. [3] carried out experiments and compared the performance and emission characteristics of Jatropha biodiesel and its blend in a single cylinder diesel engine. They reported that low emission of exhaust gases such as CO, CO₂, UHC and smoke opacity for the biodiesel compared to neat diesel outcomes. Behçet [4] reported that the performance characteristics of a compression engine were inferior, and the pollutants level in exhaust emission was reduced (except NO) for anchovy fish biodiesel against neat diesel. Abu-Zaid [5] revealed that the addition of water (5, 10, 15 and 20% of water content by vol.) had helped to increase the efficiency of combustion and caused a performance improvement and a reduction of exhaust temperature. Alahmer et al. [6] conducted experimental investigations using water-emulsified diesel (5–30%) on a diesel engine whose working speed lies within a range of 1000–3000 rpm, and they observed an ameliorated performance and a significant drop in NO_x emission. Armas et al. [7] conducted experimental investigations on a Renault turbocharged car IDI diesel engine using water (10%) emulsified diesel and found a slight improvement in the BTE and a reduction of pollutant emissions due to prolonged ignition delay. Srinivasa Rao and Anand [8] conducted experiments using Pongamia biodiesel and water-emulsified biodiesels and reported a marginal improvement in brake thermal efficiency for water-emulsified biodiesels against the neat biodiesel due to the effect of micro explosion phenomenon and an enhancement in the combustion efficiency. In addition, they mentioned that there was a reduction in the emissions of NO_x and smoke for the water-emulsified biodiesels as against biodiesel. Bidita et al. [9] studied the effects of water emulsified diesel in a diesel engine, and they stated that the combustion inside the engine cylinder was better for water emulsified diesels because of the lower viscosity. They also reported the level of CO₂, CO, and NH₃ in the engine exhaust emission for the water emulsified diesel, and it was found to be lower than the neat diesel. Matheaus et al. [10] conducted experiments on a Caterpillar 3176 engine and reported that NO_x and particulate matter emissions were reduced for the PuriNOx fuel (20% water + 80% diesel) compared to that of neat diesel because of the lowered temperature in the cylinder by the addition of water.

Based on the above literature review, prolonging the ignition delay with water emulsified biodiesel would further cause an enhancement in premixed combustion stage, high heat release rate and cylinder peak pressure. In parallel, a group of scientists tried to apply nanotechnology in the area of engines to improve the engine's working characteristics. Selvan et al. [11] experimentally investigated the influence of cerium oxide (25 ppm) as additive in neat diesel and a fuel blend (70% of neat diesel + 10% of Castor oil (biodiesel) + 20% of ethanol (D70C10E20)) in a variable compression ratio engine, and based on the obtained experimental data they concluded that the lowest BSFC was observed as 0.359 kg/kWh for the D + CERIA25 blend and 0.393 kg/kWh for neat diesel at the bmep of 0.44 MPa due to the addition of cerium oxide that promotes combustion. In addition, they found that the exhaust gases such as unburned hydrocarbon, CO and smoke were decreased with the addition of cerium oxide against that of neat diesel due to cerium oxide which could act as oxygen buffer. Similar work was presented by Sajith et al. [12], who conducted experiments using cerium oxide (20–80 ppm) nanoparticles as additive in Jatropha biodiesel in a compression ignition engine for an operating speed of 1500 rpm and reported that the BSFC was decreased and BTE was increased by the addition of cerium oxide nanoparticles. They also reported that level of unburned hydrocarbons and NO_x in the exhaust gases was significantly decreased with the addition of cerium oxide nanoparticles because of the nanoparticles in the base fuel that performed as an oxygen buffer and an effective catalyst due to its higher surface area to volume ratio. Subsequently it caused an improvement in the fuel efficiency and the reduction in level of pollutants in exhaust emissions. Kao et al. [13] carried out experiments to evaluate the combustion and the emission characteristics by using aqueous aluminium nanofluid in diesel and mentioned that the nanoparticles served as a catalyst, and the particles caused the disintegration of water and generated hydrogen. Subsequently, they mentioned that hydrogen burned in engine cylinder in the presence of an active aqueous aluminium nanofluid in diesel fuel. In addition, they obtained a significant reduction of the level of smoke and nitrous oxide in the exhaust emissions of the engine. Venkatesan and Kadiresh [14] conducted experiments in a CI engine using aqueous cerium oxide nanofluid (50 cc per litre) as additive in diesel and diesel–biodiesel blends and compared the working characteristics with diesel. They noticed that the brake thermal efficiency was increased, and the unburned hydrocarbon, NO_x and smoke levels in the exhaust emissions were decreased due to the presence of aqueous cerium oxide as an effect of its high catalytic activity. It reacts with water at high temperature and generates hydrogen that leads to the improvement in the fuel combustion. A similar study was carried out by Sarvestany et al. [15] and exposed the influence of magnetic nanofluid fuels (0.4 and 0.8 vol.%) as additive in neat diesel on the performance and emission characteristics of diesel engine. They have reported that addition of the nanoparticles to diesel showed noticeable influence on diesel engine characteristics even at small quantities, and the nanoparticles concentrations of 0.4 vol.% showed better combustion characteristics than 0.8 vol.%. They also reported that NO_x and SO₂ emissions were considerably reduced.

Aluminium nanoparticles react with water/emulsion fuels at higher temperatures and generate hydrogen, which promotes the combustion of fuel in the engine [13], [16]. Tyagi et al. [17] studied ignition properties of diesel and reported that ignition probability was high for aluminium, and aluminium oxide nanoparticles blended diesel when compared to diesel. Sadhik Basha and Anand [18] conducted experiments in a DICI engine by adding carbon nanotubes to diesel and reported a considerable enhancement in the performance and reduction in exhaust emissions. Based on the reported literature, the biodiesel emulsion fuels are considered as the propitious alternative fuels for the diesel engines in the future. In this direction, very few works on their performance, emission and combustion characteristics are available in the existing literatures. In addition, there are very few reports concerned with the improvisation of biodiesel emulsion fuel properties by adding potential nano additives. The current work is aimed to present a feasible path to investigate the effect of nanoparticles (AlO(OH)) with the Jatropha biodiesel water emulsion fuel on the working characteristics of a DICI engine due to the potentiality and compatibility of nanoparticles.