Liquefied petroleum gas (LPG) is commonly used in domestic kitchen due to its low health and environmental impacts and high heat content compared to other traditional fuels. The growing demand of LPG, notwithstanding its limited reserve, influences the need for performance improvement of the LPG cookstoves. In an LPG cookstove, the fuel–air mixture is prepared in a self-aspirated burner, and burns as a rich premixed flame above the burner. The fuel–air ratio of the reactant mixture influences the burning characteristics and thermal efficiency of the cookstove. This part of work deals with a numerical study of flow and mixing characteristics in the mixing tube and burner assembly of a domestic LPG cookstove. The fuel is injected axially through a narrow nozzle inside the mixing tube causing entrainment of ambient air through the side ports and the end port. The effects of different side-port geometry, nozzle position, inlet fuel pressure, and nozzle throat diameter on the air ingress have been systematically investigated, and the optimum design has been identified. Results of the study provide important information on the design of the practical nozzle and mixing tube assembly of high-efficiency LPG stoves.