Operating Experience With The Turbine Technologies Sr 30 Turbojet Engine Test System

The experience gained from the operation of a commercially available turbojet engine laboratory system is described. This system, the Turbine Technologies, Ltd. Mini-Lab, is suitable for use in undergraduate mechanical and aeronautical engineering laboratories. Key turbojet engine performance parameters can be computed from the data measured during test runs. The use of this system provides an excellent opportunity for students to apply the principles of thermodynamics. The Mini-Lab was acquired by the Mechanical Engineering Department of Loyola Marymount University (LMU) during the fall semester of 1999. It was checked out and interested faculty members were trained in the use of the system. The system was installed in the Thermal Sciences Laboratory at LMU and approved for operation by the university’s Environmental Health and Safety Officer. The installation included providing the necessary utilities, building a baffled intake manifold for sound suppression and building a double-walled exhaust manifold for exhaust gas expulsion, thermal protection and sound suppression. The Mini-Lab includes the SR-30 turbojet engine, the auxiliary subsystems required for the operation of the engine, controls, a safety enclosure, the instrumentation needed to acquire the experimental data and the data acquisition interface. The engine consists of a conical diffuser, a centrifugal compressor, a reverse flow annular combustor, an axial flow turbine and a converging conical exhaust nozzle. The system has been used in LMU’s senior mechanical engineering laboratory for the past two years and for demonstrations during open house type events. Engine speed, various pressures and temperatures, fuel flowrate and thrust are measured. Using these measured data, thermodynamic relationships, and property data, the following performance parameters can be determined: compressor, turbine and exhaust nozzle adiabatic efficiencies; fuel-air ratio; air mass flowrate; engine thermal efficiency; specific thrust; and thrust specific fuel consumption. In addition, the thrust can be computed from exhaust nozzle data and compared with the measured thrust. Overall, the operational experience and test results have been very good. There are some exceptions to the test results that are most likely related to measurement errors. The most notable exceptions are the values of the turbine and nozzle isentropic efficiencies (computed from the measured data) which are too large (sometimes exceeding 100%). A second exception is the value of the thrust computed from the measured data, which does not agree with the measured value of the thrust. The use of unshielded thermocouples is one source of measurement error that would affect both of these results. The method of measuring thrust is a second (possible) source of error. P ge 798.1 Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright  2002, American Society for Engineering Education Figure 1. The TTL Mini-Lab Test System Figure 2. The TTL SR-30 Turbojet Engine Background In 1999, Loyola Marymount University (LMU) made the decision to add a turbojet engine to its undergraduate mechanical engineering laboratory. A laboratory turbojet engine system is a desirable addition to an undergraduate mechanical or aeronautical engineering laboratory for three reasons. First, experimental studies using such a system are an excellent opportunity to apply thermodynamics principles. Second, EAC/ABET likes to see students experimentally studying thermodynamic systems. Third, the turbojet engine is an important contemporary product. Gas turbine engines provide the propulsion for the majority of commercial and military aircraft. Variations of aircraft gas turbine engines include turboprop, turbojet and fan jet engines. Conceptually, the turbojet engine is the simplest of these three propulsion systems and, thus, was selected for inclusion in LMU's undergraduate Thermal Sciences Laboratory. After reviewing commercially available products that were suitable for LMU's application, a Turbine Technologies, LTD (TTL) Model 2000DX Mini-Lab system (Reference 1) was acquired. This system is shown in Figure 1 (with safety shield tilted up and back). The heart of this system is the TTL Model SR-30 turbojet engine, Figure 2. The specifications for this system are described in Reference 1 and the system is described in Reference 2. Installation The Mini-Lab system is advertised as a "turnkey" system and training for personnel who may be working with it is included with its purchase. The system includes the auxiliary subsystems required for the operation of the SR-30 engine. These include fuel, lubrication and ignition subsystems. It requires 110 v, 60 Hz AC electrical power and a source of 100 psig compressed air (for starting the engine). However, it is not suitable for indoor operation as delivered because of the noise and exhaust gases. The noise level can be reduced by adding an acoustical intake manifold and a dual pipe insulated exhaust. The exhaust system directs the exhaust gases out of the laboratory building. Mr. Michael Vocaturo of Princeton University provided valuable P ge 798.2 Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright  2002, American Society for Engineering Education Figure 5. Jet Engine Installation Ready for Testing Figure 3. Acoustical Intake Manifold Figure 4. Mini-Lab with Intake and Exhaust System suggestions for designing both an intake manifold and an exhaust system (Reference 3). His suggestions were based on their design and operating experience. The intake manifold is a reverse flow, folded wave guide chamber approximately 6 ft. high, 4 ft. wide and 2 ft. deep. It is fabricated of high density particle board. The inside surfaces are lined with fiberglas, covered by canvas, for sound absorption (Figure 3). The intake air enters the manifold through an 8 inch by 18 inch rectangular opening, flows downward through the right chamber, flows into the left chamber, reverses direction and exits through a 13 inch diameter opening, flowing into the Mini-Lab system (Figure 4). The exhaust system consists of concentric 8 and 12 inch diameter stainless steel ducts with a high temperature mineral wool insulation between ducts (see Figure 4). A section of 8 inch duct extends into the test chamber to capture the exhaust jet and to entrain cooler air into the exhaust duct. This design absorbs sound and provides some thermal protection. The installed Mini-Lab system is shown in Figure 5. The SR-30 turbojet engine is enclosed in a steel and polycarbonate cabinet to provide protection to the operators in the event of a mechanical failure. This enclosure transmits sound. The noise level in the laboratory room where the system is installed is 100 dBA when the engine is operating at top speed. The corresponding OSHA Action Limit is 1.15 hours. Typical test programs can be completed in about 0.5 hours. Nevertheless, students conducting or observing tests are required to wear ear plugs. The installed engine was approved for student use by the university's environmental health and safety officer. P ge 798.3 Proceedings of the 2002 American Society for Engineering Education Annual Conference & Exposition Copyright  2002, American Society for Engineering Education Figure 6. Drawing of the SR-30 Turbojet Engine, Reference 1. The SR-30 Engine, Its Instrumentation and Operation The SR-30 turbojet engine, Figure 6, produces a maximum thrust of approximately 130 N (about 30 lbf). Referring to Figure 6, air enters the diffuser of the engine from the left and the products of combustion exit the nozzle of the engine to the right. From the diffuser, the air flows into the centrifugal flow compressor where a typical pressure ratio is about 3.5:1. The high-pressure air enters the reverse-flow annular combustor where the products of combustion leave the combustor at temperatures in the range of 600-800 C (1100-1500 F). The products of combustion enter the single stage axial flow turbine where a typical pressure ratio is 1:2.3. From the turbine, the gases flow through the converging conical nozzle exiting the engine with a typical computed exhaust velocity of 450 m/s (about 1475 ft./sec.) and a Mach number of about 0.8. The instrumentation provided with the SR-30 engine includes temperature and pressure sensors at the following locations: compressor inlet, combustor inlet, turbine inlet, exhaust nozzle inlet and exhaust nozzle exit. The temperature sensors are Type-K thermocouples and the pressure sensors are piezoresitive pressure transducers. The engine speed sensor is a 2-pole generator driven by the engine. Fuel mass flowrate is determined using a pressure transducer system that monitors the fuel injector return flow pressure. Engine thrust is measured using a strain gage type load cell. The load cell measures the force about halfway up the front engine support and is visible in Figure 2. Calibration factors are provided for each of the sensors (Reference 4). The data acquisition interface is located on the side of the cabinet. In addition, there are digital meters on the MiniLab console that indicate exhaust gas temperature, engine speed and thrust and analog meters that indicate oil pressure, combustor pressure, fuel pressure and compressed air pressure. A computer data acquisition system is available from TTL for collecting and processing the data. However, in order to give the students a better understanding of what is involved in data processing, the data generated by the LMU system is collected us ing instruments that measure sensor output directly (except for the thermocouples). The output of the pressure transducers, load cell and fuel flow system are fed through a switching box to a Kiethley Model 175A Autoranging Digital Multimeter. The output of the thermocouples was measured using an Omega Model DP25-TC Digital Therm