Among the renewable energy sources, sustainable biofuels find direct application as an alternative to diesel/petrol. Biofuel is a liquid fuel created by chemically processing vegetable oil and altering its properties to make it perform more like petroleum diesel fuel. Vegetable oils are promising substitutes, and a few crops are being grown solely for biodiesel creation. In the first paper, "Volumetric Efficiency of Four-Stroke Diesel Engine Using Jamun Seed Methyl Ester Oil (JSMEO) with Varied Piston Configurations and Injection Pressures", the authors, Subbarao B, Ramjee E and M V S M Krishna, have carried out an investigation using different types of piston head shapes in a Kirloskar-TV1 type, single cylinder, water cooled diesel engine, at various injection pressures of 180, 200, 220 and 240 bars. The study observed that the volumetric efficiency, at full load condition of the engine using Jamun-based biofuel, of Toroidal piston head with low heat rejection engine mode of operation was lower than other types of pistons (hemispherical piston head with conventional engine, shallow depth piston head with conventional engine, toroidal piston head with conventional engine and shallow depth piston head with low heat rejection engine). This is mainly due to good swirling force in the piston head, and the maximum increase in efficiency is observed at 80% load in all the experimental investigations.

The use of renewable energy such as solar energy can also be seen as a step towards sustainable energy development. The use of solar energy can be best achieved by selecting the finest solar technology and by studying the governing factors responsible for altering the efficiency of the system. Besides, the solar energy finds many applications in the residential and industrial heating and cooling systems. One of the systems utilizes solar energy to generate hot water for domestic and industrial purposes. In the next paper, "Performance Analysis of Solar Water Heater Using U-Shaped Heat Pipe", the authors, Sunil Nain and Pinku Kumar, have studied the performance of a solar water heater fitted with evacuated tube, with and without a U-shaped copper heat pipe insertion. By fixing 100 L as a constant mass/quantity of water, they have analyzed the variations in temperature and efficiency of water heater at different flow rates and noted that the efficiency of the solar water using heat pipe improved more considerably than in the case of solar water heater with simple evacuated tubes, and that at low flow rates, the temperature of water increases significantly.

EN24 is a high tensile strength steel alloy with good ductility and wear resistance characteristics in hardened condition. In the machining process of a material in hardened condition, quality and productivity are the two conflicting objectives, between which one has to be compromised to achieve the other. In order to achieve high quality and productivity, it is necessary to determine the optimal parameter settings of the machining parameters-surface finish and Material Removal Rate (MRR) in end milling. In the next paper, "Parametric Optimization of End Milling Operation on EN24 Steel Shaft of Grinding Machine", the authors, Kishan Vaghamshi and G D Acharya, have studied the effect of milling operation parameters (cutting speed, feed rate and depth of cut) on MRR and surface finish in milling of EN24 steel. Using Minitab software with input parameters (3 factors at 5 levels), the authors have evaluated minimum surface roughness and maximizing MRR using Taguchi design methodology. The study noted that the maximum MRR with high surface finish in machining is highly desirable for EN24 steel shaft.

Friction Stir Welding (FSW) is a solid-state joining technique, wherein two difficult-to-weld and dissimilar material workpieces are butted together. The resultant products of FSW are found to exhibit high joint strength and high microhardness, and the products are also devoid of any melt-related defects. FSW is capable of fabricating Cu alloys, Ti alloys, Al alloy, Mg alloys, stainless steel and mild steel. More recently, the process is being utilized in welding of polymers also. FSW is used in a variety of industrial applications such as aerospace, automotive, shipbuilding and offshore, rolling stock for railways, general fabrication, robotics and computers. In the last two decades, several variants of FSW have become popular, and a few researchers even augmented auxiliary energy sources with conventional FSW to obtain higher welding speeds and tool life with reduced cost. The paper, "Friction Stir Welding in Al Alloys: A Study", by Harvinder Singh, Santosh Kumar and Rakesh Kumar, presents a brief review of the state-of-the-art FSW. The classification of FSW, process variables and applications of friction welding, classification of Friction Stir Process (FSP) materials, effects of tool pin configuration and merits and demerits of FSW are presented.