INVESTIGATIONS ON USABILITY OF POROUS MEDIA IN KEROSENE PRESSURE STOVES FOR IMPROVEMENT OF THERMAL PERFORMANCE

Abstract

In developing countries, kerosene is considered as one of the principal cooking fuels and it is normally burnt in two kinds of stoves: wick type and pressure type. The pressure type stoves perform reasonably well; however the growing awareness about conservation of energy and reduction of pollution has necessitated their further improvements. Towards the above goal, in this study, a conventional kerosene pressure stove was modified to incorporate a bi-layered porous media consisting of alumina (Al2O3) and silicon carbide (SiC) enclosed in 6 different types of casing in the combustion zone. The thermal performance of the stove was evaluated with each type of casing. The main aspects of the thermal performance include temperature, emission and efficiency measurements. The emission and efficiency studies were conducted for different fuel and air flow rates. It was observed that the burner could be operated in a much leaner condition without affecting the stability of the flame. CO and NOx were measured at different air fuel ratios. The lowest CO emission (30 ppm) was observed for the fuel flow rate: 220 g/hr and air flow rate 120 lpm. CO emission was found sensitive to heat input and air flow rate. While, NOx behaviour was found insensitive to both heat input and air flow rate. The lowest NOx recorded was 1.2 ppm. The temperature measurements were taken at different radial and axial locations. The average surface temperature was found ~800 oC and it was found to increase with increase in air and fuel flow rates. The efficiency test of the burner was conducted as per the standard water boiling test (WBT) in accordance with the BIS standard: IS 10109: 2002. The highest efficiency (~57%) was recorded for the fuel flow rate: 160 g/hr and air flow rate rate: 150 lpm and this was obtained for a conical casing. Further, the efficiency also varied with vessel sizes and the different spacings between the vessel and the burner.The optimum distances giving the best thermal performance have been identified. An analysis has been carried out to calculate the efficiencies of the burner,working in different operating conditions, from the second law point of view. It was found that with increase in air flow rate the energy efficiency or the first law efficiency increases, while the exergy efficiency decreases. Similarly, the exergy efficiency increases with increase in fuel flow rate which is reverse in case of the first the efficiency. Thus, considering both first law and second law efficiencies, the air flow rate 120-130 lpm was found optimum. The conical casing shows the highest second law efficiency too. Finally, the thermal performances of the stove with new burner were compared with a conventional BIS specified stove. For the same heat input, the conventional stove showed higher CO (80-90 ppm) and NOx (3-4 ppm) but first (thermal efficiency) and second law efficiencies (exergy efficiency) were comparable.....