IAC-05-C4.3.03 THRUST AUGMENTATION NOZZLE (TAN) CONCEPT FOR ROCKET ENGINE BOOSTER APPLICATIONS Mr. Scott Forde Hydrocarbon Engine Chief Engineer Aerojet, Sacramento, CA, United States [email protected] Mr. Mel Bulman Advanced Propulsion Chief Engineer Aerojet, Sacramento, CA, United States [email protected] Mr. Todd Neill Exploration Systems Chief Engineer Aerojet, Sacramento, CA, United States [email protected] (065-05) ABSTRACT Aerojet used the patented Thrust Augmented Nozzle (TAN) concept to validate a unique means of increasing sea-level thrust in a liquid rocket booster engine. We have used knowledge gained from hypersonic Scramjet research to inject propellants into the supersonic region of the rocket engine nozzle to significantly increase sea-level thrust without significantly impacting specific impulse. The TAN concept overcomes conventional engine limitations by injecting propellants and combusting in an annular region in the divergent section of the nozzle. This injection of propellants at moderate pressures allows for obtaining high thrust at takeoff without overexpansion thrust losses. The main chamber is operated at a constant pressure while maintaining a constant head rise and flow rate of the main propellant pumps. Recent hot-fire tests have validated the design approach and thrust augmentation ratios. Calculations of nozzle performance and wall pressures were made using computational fluid dynamics analyses with and without thrust augmentation flow, resulting in good agreement between calculated and measured quantities including augmentation thrust. This paper describes the TAN concept, the test setup, test results, and calculation results. FULL TEXT NOMENCLATURE INTRODUCTION C* = Characteristic Velocity Downloaded by UNIV OF CALIFORNIA LOS ANGELES on May 2, 2014 | http://arc.aiaa.org DOI: 10.2514/6.IAC-05-C4.3.03 Isp = Specific Impulse (lbf-sec/lbm) Conventional rocket engines for a launch LOX = Liquid Oxygen vehicle booster stage need to deliver high thrust RP-1 = Rocket Engine Grade Kerosene when taking off with the greatest vehicle weight, TAN = Thrust Augmented Nozzle typically near sea-level operation. They then TCA = Thrust Chamber Assembly operate until reaching altitudes that have TPA = Turbopump Assembly relatively low ambient pressures around the TVC = Thrust Vector Control engine. T/W = Engine Thrust per Weight The vehicle requires engines with as high = Nozzle Area Ratio (Nozzle Exit specific impulse (Isp) as practical to minimize Diameter / Combustion Chamber propellant mass; however, a high-vacuum Isp Throat Diameter engine requires a large area ratio nozzle. These two requirements conflict since the large area 1 ratio nozzle operating at sea-level pressure is axial pressure contour along the nozzle from less efficient in producing thrust. This is due to throat to exit plane. This increased nozzle the gases over-expanding to a pressure below pressure directly leads to increase thrust. The ambient. This results in a portion of the nozzle ignition source for the secondary propellant is generating negative thrust. At extreme area the hot exhaust from the core engine gases. ratios, the exhaust jet will separate from the nozzle, causing large transient loads and high local heat fluxes, potentially damaging the nozzle. A variable area nozzle would add complexity, cost, weight, and size to the engine while still yielding less thrust at sea level than at vacuum. TAN DESCRIPTION Aerojet’s patented TAN concept1, shown in Figure 1, overcomes these conventional engine Fig. 2: Schematic of TAN Injection Elements limitations by injecting propellants and combusting in an annular region within the 200 divergent section of the nozzle. This injection of 180 Augmentation ε = 25:1 Injector 160 ε propellants at moderate pressures allows for Location ε injection = 6:1 MRcore = 5.86 ) a Pc core = 981 psia obtaining high thrust at takeoff without i 140 s MRTAN = 6.13 p ( e overexpansion thrust losses. The main chamber r 120 u s s e is operated at a constant pressure while r 100 P c i t Augmentation On maintaining a constant head rise and flow rate a t 80 S l l of the main propellant pumps. Engine thrust a W 60 augmentation greater than 100% of a normal engine is achievable. 40 20 Pambient No Augmentation Primary Gas 0 High Altitude Operation 0 1 2 3 4 5 6 7 8 9 10 TAN OFF Throat Axial Distance from Throat (inches) Primary Core Combustion Fig. 3: Nozzle Pressure as a Function of Axial Distance From Main Thrust Chamber Throat TAN ON Sea Level Operation With and Without TAN Fuel and Oxidizer Secondary Gas Reduces Injectors Secondary Expansion of Core and Combustion Increases Nozzle Pressure The TAN concept is scaleable to a wide range Fig. 1: TAN Diagram for Sea-Level and High- of thrust-class engines from the very small Altitude Operation Modes thrust class of 2000 to 1,500,000 lbf and larger. The TAN concept is applicable to various The concept is an extension of the liquid oxygen engine cycle schemes such as gas generator (LOX)-Augmented Nuclear Thermal Rocket cycle, stage combustion cycles, and open and 2-6 (LANTR) where LOX was injected into the closed expander cycles. divergent nozzle section of the superheated The propellant combinations that have been liquid hydrogen (LH2) exhaust of a nuclear tested include gaseous oxygen (GOX) and LOX Downloaded by UNIV OF CALIFORNIA LOS ANGELES on May 2, 2014 | http://arc.aiaa.org DOI: 10.2514/6.IAC-05-C4.3.03 thermal rocket thrust chamber assembly (TCA) for the oxidizer with hydrogen and RP-1 for the to combust with the hydrogen and generate fuels. All other bipropellant combinations seem additional thrust. TAN takes the next step and to be feasible with the TAN concept. This injects both oxidizer and fuel into the divergent includes options of using propellant for the TAN nozzle section of the TCA of a conventional section that are different than the propellant bipropellant booster rocket engine where the used for the core engine. One such tripropellant secondary propellants mix and combust in the option uses LOX for both the main engine and nozzle. This reduces expansion of the core the TAN oxidizer with hydrogen for the fuel on gases and increases nozzle pressure. the core engine and a heavier hydrocarbon fuel Figure 2 shows a cross-section of a nozzle for the TAN injector. downstream of the throat with the fuel and The TAN propellants can be supplied based on oxidizer injection elements. Figure 3 shows the the optimum vehicle configuration. The three 2 approaches that have been evaluated are constant nozzle exit pressure can allow an NK- supplying propellants from modified core engine 33 with a nozzle area ratio () of 58:1. A boost pumps, incorporating TAN specific conventional NK-33 would have separated flow pumps, or supplying pressure-fed propellant. with a 58:1 nozzle. Engine system power balance analyses on 160 t 1,000,000-lbf-class LOX-hydrocarbon staged h 150 g i combustion cycle engines with TAN have been e W / t s 140 u performed. These analyzes indicate that r h T providing the LOX and hydrocarbon fuels to the l e 130 v e L AR=30 TAN injectors from the boost pump discharge is a e AR=40 S 120 feasible with minimal impact on the main e AR=50 n i AR=60 g turbopump assembly (TPA), preburners, and n E 110 main chamber operating performance. Adding TAN-specific pumps would separate engine and 100 TAN development, and be the minimum impact 0 10 20 30 40 50 TAN % of integrating a TAN subsystem into an existing Fig. 4: Sea-Level Thrust to Weight vs. Percent engine system. Thrust Augmentation on an NK-33 With TAN Injector and TAN Pumps TAN BENEFITS Weighted Isp vs %TAN 80%Isp(Vac)+20%*Isp(SL) 333 The TAN concept represents no less than a Nozzle Attached Flow 332 change in the rocket propulsion paradigm and Approx 6 psi Exit Pressure Line 331 has wide ranging benefits. This concept can Nozzle Separated Flow c 330 e S create an engine with a higher thrust-to-weight , 329 p s I ratio (T/W) for an engine, which can be traded d 328 e t directly for increased payload. h 327 AR=30 g i Constant Exit Pressure Line e As Baseline NK-33 Exit Pressure AR=40 NK-33 is a 350-klbf-class LOX-kerosene W 326 AR=50 oxygen-rich staged combustion cycle engine 325 AR=60 with one of the highest T/W of any booster 324 engine. This engine was used to show that an 323 0 10 20 30 40 50 even higher T/W is achievable with TAN added TAN % to the engine. The sea-level T/W for the original Fig. 5: Weighted Isp vs. Percentage of Thrust NK-33 is 128:1. The T/W of a TAN equipped Augmentation of an NK-33 With TAN Injector NK-33 can be increased to greater than 150:1 and TAN Pumps depending on the TAN augmentation, which is greater than a 17% improvement. A similar comparison was performed using a Figure 4 plots the NK-33 with TAN T/W as a LOX-hydrogen gas generator cycle engine in function of the percent thrust augmentation with the 650-klbf-thrust class similar to an RS-68. various nozzle area ratios. Figure 5 plots the The results have the same trends as the weighted Isp (80% vacuum and 20% sea level). previous example; however, the engine T/W The 80/20 weighting was selected based on improvement is even more dramatic. The previous studies of a mission-averaged Isp for a baseline LOX-hydrogen engine sea-level T/W two-stage-to-orbit launch vehicle.