S.Bibin Sagaram’s scientific contributions

The influence of injector coking deposits on the spray field of single-hole Mechanical Port Fuel Injectors (PFI) and multi-hole Common Rail Direct injection (CRDi) injectors was studied using light scattering technique coupled with Image Processing and Analysis. Instead of employing the traditional accelerated coking process to study Injector spray field deterioration, in-service injectors were selected and cleaned using a commercial Fuel System Cleaning procedure. Variation in atomization characteristics of coked and cleaned injectors were observed based on the spatial distribution of fine, medium and coarse droplets in the near-field region of the Injector spray zone and analyzed as a function of the intensity of scattered light. The improvement in the atomization perceived by this method was compared with traditional techniques like spray cone angle measurement, speed characterization of spray jets and weight reduction of injector nozzles and needles. It was observed that after the Fuel System Cleaning procedure, a reduction in the number of coarse droplets in the near-field region and an increase in the number of medium and finely sized droplets was observed, suggesting better atomization of fuel in the near field spray zone.

With rising fuel prices and decreasing fuel reserves, vehicles are being made more fuel efficient. Vehicle aerodynamics plays a crucial role in determining fuel consumption. This paper investigates the influence of passive flow control technique of imparting a dimpled body design in aerodynamic drag reduction by delaying flow separation and reducing the amount of wake region created behind the vehicle. For this, Ahmed bodies with 25° and 35° of slant angles have been used. Experiments were performed to compare the drag variations at various velocities when dimples of a fixed aspect ratio were imparted to the top surface of the Ahmed body behind the rear legs. For the 25° Ahmed body, the highest drag reduction of about 40% was obtained for the lowest flow velocity of 3m/s. Previous literature shows a sudden increase in drag force when the slant angle is increased beyond 30° .Hence tests were conducted on the Ahmed body with 35° slant angle with and without dimples. It revealed that the dimples had no effect in reducing its drag at low flow speeds. In fact, it was found that the dimpled body suffered an increased drag at higher velocities. Based on the studies conducted and by also taking the ease of fabrication into consideration, dimples were imparted on the super-mileage vehicle developed by us for ‘Shell Eco Marathon Asia 2015’. The dimpled design imparted an increase in fuel efficiency of about 7%. This paper thus serves to prove the aerodynamic as well as fuel efficiency advantage that the dimpled design imparts to a vehicle.

Magnus rotor is essentially a rotating cylinder that generates lift due to Magnus effect. The effect has been generating curiosity in a wide variety of fields ranging from sports to alternate energy. The wind turbine under investigation replaces tradition blades that have an airfoil cross-section, with such Magnus rotors. In this paper, Magnus wind turbines with three and five rotors have been analyzed at various velocity ratios and tip speed ratios. The primary motive is to find the best operating conditions for obtaining a higher lift to drag coefficient for both three and five rotor turbines, so that it can generate more power with the least available wind. It has been observed that the higher ratio of coefficient of lift to coefficient of drag values were obtained for lower values of tip speed ratio, which is in contrast to the requirement of higher tip speed ratios for turbines with airfoil cross-section. This translates to the fact that Magnus wind turbines can be an efficient solution to the generation of wind power with less noise generation, since the noise generated by a wind turbine decreases with decrease in the tip speed ratio.