Experimental Investigation of Coffee Husk Biodiesel as A Renewable Fuel In Compression Ignition Engine

Abstract

In the present study, coffee husk (CH) and spent coffee ground (SCG) are used for the production of biodiesel. The CH is a by-product of the coffee processing industry, and SCG is obtained after the coffee is brewed. Field Emission Gun Scanning Electron Microscope (FEG-SEM) is used to investigate the elemental composition of the CH and the SCG samples and identify the presence of different elements with their distribution and concentration. The compositional analysis indicates that the CH comprised 49.84% of carbon and 48.06% of oxygen by weight. On the other hand, it is found that the SCG had 67.72% of carbon and 26.18% of oxygen by weight. The CH is selected for further study for the production of oil due to its higher oxygen distribution than SCG. From 1Kg of CH, 250g of oil is produced. By using the transesterification process, the produced oil is converted into biodiesel. Subsequently, 700 mL of coffee husk oil methyl ester (CHOME) biodiesel was produced from 1000 mL of coffee husk oil. After characterization of obtained biodiesel, the experiments are conducted in a single-cylinder direct injection diesel engine at a constant speed by varying the loads (0%, 25%, 50%, 75%, and 100%) for different biodiesel-diesel blends (B10, B20, B30, B40, B50, B80, and B100), and the results are compared with the baseline diesel. The brake thermal efficiency (BTE) of the blends, B10, B20, B30, and B50, is reduced by 0.6, 0.7, 1.29, and 3%, respectively, compared to the regular diesel. Similarly, the brake specific energy consumption (BSEC) is increased by 0.1, 0.3, 0.44, and 0.77% for B10, B20, B30, and B50, respectively. Exhaust gas emissions are reduced for all biodiesel-diesel blends with a marginal increase in NOx emission. Compared to regular diesel, at full load, CO, HC, and smoke opacity of B30 are reduced by 13.2%, 4%, and 12%, respectively. Whereas NOx and CO2 of B30 at full load are increased by 3.8% and 8.63% respectively The viscosity of CHOME biodiesel is found to be higher than diesel; hence a preheating mechanism is set to reduce the viscosity and density of the fuel before injecting it into the combustion chamber. Preheating the neat CHOME biodiesel (B100) to 95 °C decreased its viscosity and density by 49.5% and 3.7%, respectively. Running the engine with preheated B100 reduces CO, HC, and smoke opacity by 34%, 34%, and 35%, respectively, compared to unheated regular diesel. The percentage of CO2 in the exhaust gas is increased by 45.5% for preheated B100 compared with unheated B0 at 100% load. Furthermore, the injection timing of the engine is altered to find the optimum injection timing of the biodiesel-diesel blend. The BSEC is increased by 0.53 kg/kWh and reduced by 1.4 kg/kWh for advanced and retarded injection timing, respectively. By advancing injection timing, the HC, CO, and smoke opacity were reduced by 7.4%, 36%, 5.7%, and 7%, respectively, compared to the B30 at standard injection timing.