Thermodynamic Analysis and Preliminary Design of the Cooling System of a Pulsejet for Aeronautic Propulsion

Abstract

This paper is a preliminary step through an effective redesign of valved pulsejet. This redesign activity relates to both thermodynamics and heat transfer. It aims to overcome their intrinsic limits: short service life of the valves and low energy efficiency of the Lenoir cycle. A detailed analysis of the operative behavior of pulsejets allowed the authors to advance an effective hypothesis about redesigning this propulsion system. A preliminary bibliographic analysis shows that the very high temperature that the walls of the combustion chamber reaches does not allow the use of more effective valves with respect to the petal valves or grid mounted reed valves. The absence of any compression, which is a characteristic property of the Lenoir cycle, is the main cause of the low thermodynamic efficiency of the system. The intrinsic fragility of these valve systems has blocked any further development of the valved pulsejet. A preliminary feasibility analysis of a cooling system, which can be used on pulsejets, is then a preliminary element both in the direction of improving both their thermodynamic performance and their robustness. The considered working conditions are: temperature of 1500 K, which oscillates with an amplitude ±500 k and a frequency of 30 Hz. The refrigerant is considered water and its average temperature is supposed 80 º C. Analysis of the temperature profile within the wall and the effects of the oscillations of gas temperature have been evaluated, together with a preliminary design of the cooling system.