Experimental Investigation of LHR Engine Run on an Antioxidant-Doped Biodiesel-Diesel Blend

Abstract

Biodiesel is derived from plant oils, animal fat, and algae by the esterification/transesterification process. It can be either used directly or in a blended form with diesel in compression ignition (CI) engines. The important merits of biodiesel when used as an alternate fuel in CI engines are (i) it does not produce SOx emissions, (ii) hydrocarbon (HC), carbon monoxide (CO), and smoke emissions are lower. However, there are a few important technical challenges found with the utilization of biodiesel in CI engines, which include (i) lower engine performance, (ii) higher oxides of nitrogen (NOx) emissions, and (iii) oxidation stability. The brake thermal efficiency (BTE) of the engine is slightly reduced and brake-specific fuel consumption (BSFC) is higher in the biodiesel-fueled diesel engine. This research work is aimed at simultaneously improving efficiency and reducing NOx emissions of a biodiesel-diesel blend run direct injection (DI) diesel engine. For this purpose, a conventional DI diesel engine is made to run in a low heat rejection (LHR) mode to inhibit heat loss to improve the thermal efficiency of the engine. The biodiesel-diesel blend considered in this study is JME20 which contains 20% Jatropha methyl ester (JME) and 80% diesel on a volume basis. On the other hand, an antioxidant is doped in the biodiesel-diesel blend to reduce NOx emissions.
Initially, thermal and structural analyses are carried out considering two different TBC pistons. Thermal barrier coating (TBC) comprising Yttria stabilized zirconia (YSZ), and YSZ + Cerium oxide (CeO2) (85%YSZ+15%CeO2) is applied on an aluminum alloy piston. Three different thicknesses of the topcoat of materials for YSZ and YSZ+CeO2 coating viz. 0.3 mm, 0.6 mm, and 0.9 mm are chosen. SOLIDWORKS software is used to draw pistons and different thicknesses of layers (top coatings). ANSYS software is used for performing structural and thermal analyses on the piston surface. The YSZ+CeO2-coated piston gives better results in thermal and structural analysis when compared to the YSZ-coated piston. Therefore, the YSZ+CeO2-coated piston is used to form an LHR engine for experimental investigations that are further carried out in this research work. Six experimental works are carried out to study the combined effect of running a DI diesel engine run in the LHR mode fueled with an antioxidant-doped JME20. For this purpose, a single cylinder, four-stroke DI developing the power of 4.4 kW at 1500 rpm is converted to LHR mode by coating the piston with YSZ+CeO2. Initially, the engine is run on diesel and JME20 to obtain baseline data. The peak cylinder pressure and heat release rate are increased by 1.8% and 2.2%, respectively, for the YSZ+CeO2-coated piston-fitted engine compared to the uncoated piston-fitted engine run on JME20. The ignition delay and combustion duration are improved by 16.8% and 3.5%, respectively, at full load when compared to the uncoated diesel engines fueled with JME20. BTE increased by about 7%, and BSFC decreased by 5.3% at full load in the LHR engine run on JME20. HC, CO, and smoke opacity are reduced by about 11.5%, 7.2%, and 4.7%, respectively, at full load for the JME20-fueled LHR engine. Nitric oxide (NO) emission is increased by 11.2% at full load for the LHR diesel engine fueled with JME20. The analysis of the experimental results reveals that the engine performance improves and diminishes engine emissions such as HC, CO, and smoke in the LHR diesel engine but increases NO emission due to the high cylinder temperature and availability of oxygen in the test fuel (JME20). Therefore, further experiments are carried out on the use of antioxidants to reduce NO emissions from the test engine. Two synthetic antioxidants, namely N-Isopropyl-N'-phenyl-1, 4-phenylenediamine (IPPD) and N, N'-Diphenyl p-phenylenediamine (DPPD), each taken at four concentrations viz., 500 ppm, 1000 ppm, 1500 ppm, and 2000 ppm are doped with JME20. The mixtures obtained with IPPD are designated as JME20A1, JME20A2, JME20A3, and JME20A4, where A1, A2, A3, and A4 indicate 500, 1000, 1500, and 2000 ppm respectively. Similarly, the mixtures obtained from doping DPPD in JME20 are designated as JME20B1, JME20B2, JME20B3, and JME20B4, where B1, B2, B3, and B4 indicate 500, 1000, 1500, and 2000 ppm respectively. Before examining the fuel mixtures test engine, they are characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Energy Dispersive Spectroscopy (EDS) for their oxidant behavior. Further, experiments are conducted in the test LHR engine. Due to the combined effects of micro-explosion and the secondary atomization of IPPD-doped JME20 fuels, HC and CO emissions are reduced by 30.6% and 22.4%, respectively, compared to those of diesel operation at full load. The smoke opacity is reduced by 11.5% at full load condition for JME20 A3 in the LHR engine. NO emission is reduced by 11.7% for JME20A3 at full load condition compared to an uncoated engine. The peak heat release rate (HRR) and the peak cylinder pressure are lesser by about 5.6% and 5.1% for JME20B4 in the coated engine (CE), respectively, at maximum engine load. NO, HC and CO emissions are reduced by 6.5%, 17.4%, and 34.6%, respectively, at full load for the JME20B4 fueled in the LHR diesel engine. The next set of experimental studies used two leaves extracted natural antioxidants doped with JME20 to reduce the NO emission and analyze the engine performance also.
Natural antioxidants are available in various biomass substances, which can be used for improving human health and fuel oxidation stability. Therefore, the next two sets of experiments are carried out using antioxidants derived from two potentially available biomass substances (i) Albizia lebbeck, and (ii) Pongamia pinnata leaves. Albizia lebbeck leaves, and Pongamia pinnata leaves are characterized by XRD, SEM, FTIR, and EDS for their oxidant behavior. Antioxidant obtained from Albizia lebbeck at various concentrations viz., 500, 1000, 1500, and 2000 ppm is doped in JME20, and the blends are designated as AL1, AL2, AL3, and AL4, respectively. Antioxidant from Pongamia pinnata leaves at 500, 1000, 1500, and 2000 ppm is doped in JME20, and the fuel mixtures are designated as PLA1, PLA2, PLA3, and PLA4, respectively. The combustion, performance, and emissions of the test engine run on antioxidant-doped JME20 fuels in the conventional engine operation and LHR mode are evaluated. Results indicate that among the four antioxidants doped-JME20 fuels, JME20AL4 gives better performance and lower exhaust emissions. The cylinder pressure and heat release rate are lesser by about 4.7% and 6.4%, respectively, at full load, for JME20 AL4. The fuel's delay period and combustion duration are improved by about 26.8% and 10.8%, respectively, at maximum load. NO, HC and CO emissions are reduced by about 17.3%, 19.3%, and 44.2%, respectively, for JME20 AL4, at maximum load. Cylinder pressure is reduced by about 5.9% and the heat release rate by 6.9% for JME20 at a concentration of 2000 ppm in the LHR engine. The engine emissions are reduced by 17.5% and 16.3% for HC and smoke, respectively, at maximum load for JME20 PLA4, in the LHR engine. NO emission is decreased by 16% for JME20 with 2000 ppm (JME20 PLA4) at a higher load in the coated engine.