Proposed Nomenclature Guide for Pulse Detonation Engines (2002)

Worldwide interest in the Pulse Detonation Engine, PDE, has grown significantly in the last several years. During this time, the aerospace community has experienced difficulty exchanging technical information due to a lack of a common nomenclature for this relatively new device. The resultant confusion has impeded the community’s ability to make technical progress. This paper provides a proposed nomenclature convention to initiate further community discussion and help facilitate common agreement. The PDE presents several nomenclature challenges. First, the PDE employs some unique components not associated with traditional Brayton cycle engines, which leads to a station designation challenge. This paper proposes an adaptation of the widely-accepted SAE standard station designation to accommodate unique PDE features. Second, the time-dependent nature of the PDE compounds the station designation challenge. Flow and physical properties, at each station within the PDE, vary depending on the engine cycle phase. This paper proposes an expansion of the SAE standard station nomenclature to accommodate the time-dependent nature of the PDE. Third, the PDE cyclic operation introduces flow characteristics not present in more conventional, Brayton cycle engines. An example is the buffer required in most PDE architectures to protect the fresh charge from the combustion products of the previous charge. This paper proposes a flow characteristic nomenclature and definition scheme. * Member AIAA, Boeing Technical Fellow, The Boeing Company, St. Louis, MO † Senior Program Manager, Pratt & Whitney, Bellevue, WA ‡ Project Engineer, Pratt & Whitney, East Hartford, CT INTRODUCTION There is a need to standardize nomenclature used in the analysis of the Pulsed Detonation Engine, PDE, to facilitate technical interchange. Toward this end, this paper proposes a system encompassing: component nomenclature, station (spatial) designation, process and event (temporal) designation and terminology for the unique PDE scheduling characteristics. This proposal is based on several years of PDE analysis and testing by Boeing and Pratt & Whitney and is based on accepted practices, such as SAE Standard AS755. It is hoped that this system will provide a starting point for further discussion. SPATIAL DESIGNATIONS By the very nature of its cyclic operation, physical stations within the PDE are performing different thermodynamic functions at different times in the cycle. To simplify the nomenclature process, the proposed system assigns a designation for each component’s physical, or spatial, location, but also adds to this spatial designation a time-dependent, temporal, designation. The following section presents the proposed spatial designation. BASIC PDE NOMENCLATURE The first example is the basic airbreathing PDE. For this example, the PDE uses the Naval Postgraduate School, NPS, architecture. The main engine flowpath, Figure 1, is comprised of an inlet, air induction valve, a detonation chamber and a nozzle. The air induction valve function is to meter the air into the detonation combustion chamber during the refresh portion of the cycle and to provide a thrust surface during the detonation portion of the cycle. The function of detonation chamber is to combust the fuel and air mixture, in this case through supersonic combustion or detonation. The nozzle function is to increase thrust production through the expansion of the exhaust products during the cycle detonation portion. During the refresh portion of the cycle, the nozzle serves to back pressure the chamber to increase thrust production. 1 38th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 7-10 July 2002, Indianapolis, Indiana AIAA 2002-3631 Copyright © 2002 by the author(s). Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Figure 1. PDE Component Nomenclature To start the detonation process, in the NPS architecture, there is a small initiator, which feeds into the detonation chamber. The initiator typically has it’s own dedicated fuel and oxidizer source. In the traditional NPS architecture, the initiator is located at the upstream end of the detonation chamber. However, other locations have been proposed. BASIC PDE STATION DESIGNATION The proposed basic PDE station designation is presented in Figure 2. This designation builds off of the ramjet station designation, with the addition of the initiator and air valve. Figure 2. PDE Station Designation For the PDE, the air valve and detonation chamber replaces the ramjet burner between stations 3 and 4. In most cases, the air valve is positioned between stations 3 and 3.5, while the detonation chamber is positioned between stations 3.5 and 4. Rationale for this designation scheme considers the air valve as part of the detonation combustion process and therefore included between the traditional combustor entrance station 3 and the combustor proper. Inlet Initiator Air Induction Valve Detonation Chamber Nozzle As the initiator stream typically has a separate feed independent of the main chamber, the initiator stream is introduced as 9X. This designation is allowed as an acceptable practice in the SAE nomenclature guide and was selected in this application to reduce confusion. As was stated above, the initiator has various locations in different PDE designs. Rather than using the SAE suggested inner to outer stream practice, which would have the initiator designations vary with their physical location, the optional practice was selected. This practice also will simplify some of the hybrid configuration designation schemes. TURBOJET WITH PDC AFTERBURNER COMPONENT NOMENCLATURE Figure 3 presents a schematic of a hybrid engine that uses a turbojet cycle for primary thrust and a Pulsed Detonation Combustor, PDC, for afterburning. In this application, all, or nearly all, of the turbojet flow stream enters and is processed by the PDC during high thrust operation. This architecture is of interest, as the PDC promises higher efficiency than the traditional afterburner. Figure 3. Turbojet with PDC Afterburner Component Nomenclature TURBOJET WITH PDC AFTERBURNER STATION DESIGNATION As in the case of the PDE and ramjet, here the PDC stations have replaced the traditional stations for the afterburner, station 6 to 7. The PDC air valve occupies stations 6 to 6_*, while the PDC combustor occupies stations 6_* to 7. 0 1 3 3_* 4 8 9 93 94 98 Station Description 0 Freestream 1 Inlet Entrance 3 Inlet Exit/Air Valve Entrance 3_* Air Valve Exit/Detonation Chamber Entrance 4 Detonation Chamber Exit/Nozzle Entrance 8 Nozzle Throat 9 Nozzle Exit Main Stream PDC Initiator Station Description 93 Initiator Chamber Entrance 94 Initiator Chamber Exit 98 Initiator Exit Throat Inlet Initiator Air Induction Valve Burner Compressor Turbine Detonation Chamber Nozzle