| dc.description.abstract | Domestic cooking is one of the basic human needs, and cookstoves based on fuel combustion are widely used. LPG (Liquified Petroleum Gas) is the most common cooking fuel, followed by PNG (Piped Natural Gas), which has an increasing consumer base in India. Thus, even a slight improvement in domestic burner efficiency can save large quantities of fuel to benefit the national economy. Also, since PNG is about three times less dense than LPG with very different combustion characteristics, dedicated burners must be designed and optimized for PNG. The present study explores novel burner designs to improve thermal efficiency and reduce pollutant emissions.
In the first part, validated three-dimensional Computational Fluid Dynamic (CFD) modelling is used to simulate the flow and fuel combustion above the burner and heat transfer from the hot gases to the vessel. A simulation with the conventional LPG burner showed that the convective heat flux profile directly correlates with the temperature and velocity distributions in the vicinity of the vessel and shows multiple peaks with very low heat transfer at the centre. Thus, a novel burner design was conceptualized by orienting the flow towards the centre to increase the near-vessel gas temperature and residence time. The burner diameter and hole inclination angle were optimized for maximising the convective heat flux, leading to about 8.4% higher predicted efficiency with LPG and PNG fuels.
In the second part, the novel burner was designed, fabricated and evaluated in a test rig which enables precise control of the fuel and air flow rates, loading height and equivalence ratio (ϕ). To quantify the heat flux distribution and the burner efficiency, an infrared camera was used to measure the temperature distribution on an aluminum plate. The heat flux distribution was calculated using the heat balance equation. The emissivity of the anodized aluminum plate was calibrated by measuring the heat flux from an electric heater with a set heating rate. The pollutant emissions and OH* distributions were also measured. The novel burner was observed to stabilize much leaner LPG flames up to an equivalence ratio ϕ = 0.8. Heat flux measurements depicted a higher and more uniform heat flux with the novel burner. The burner efficiency is defined as the ratio of area-integrated heat flux on the plate to the input power. To quantify
the efficiency improvement at given conditions of LPG flow rate and equivalence ratio, the highest burner efficiency of the novel burner across the three loading heights is compared with the highest burner efficiency of the conventional burner across the loading heights. At ϕ = 1, 1.2 and 1.4, the novel burner provides maximum efficiency improvements of 4.1%, 3.7% and 2.7%, respectively, over the conventional burner. At these maximum efficiency improvement
conditions, the CO emissions are of similar order with the two burners. Next, the novel burner was evaluated with PNG fuel. The stable flame regime and heat flux profiles were found to be similar to those with LPG. At ϕ = 1.2 and 1.4, the maximum improvement in the burner efficiency was observed to be 3.8% and 2.8%, respectively. CFD simulations using reduced mechanisms accurately captured the flame structure (OH* distribution) and heat flux trends observed with both LPG and PNG fuels.
In the final part, two design additions were evaluated, i.e., inclusion of a radiative disc and a heat-collecting shield around the burner. Heat flux measurements revealed that the radiative disc reduces the heat flux due to the disruption of the flow field near the vessel. On the other hand, including the heat-collecting shield to the novel burner led to a maximum improvement in the burner efficiency of 8.7% and 8% with LPG and PNG fuels, respectively, compared to the conventional burner. The CO emissions were less or on par with those of the conventional burner, except at high flow rate of PNG. Finally, the efficiency of the novel burner was assessed in the actual cookstove following the Indian Standard tests (IS 4246, IS 17153). The combination of the novel burner and the shield yields the highest IS test efficiencies of 68.9% and 72.2% with LPG and PNG, respectively, resulting in corresponding fuel savings of 4.6% and 7.9%. Thus, a fundamental understanding of the fluid flow, combustion and heat transfer phenomena have successfully guided the optimization of the burner design, leading to a high-efficiency, low-emission burner suitable for use with both LPG and PNG fuels. Additionally, the study has provided a robust methodology for designing burners for heating applications. | en_US |
