University of Colorado Department of Aerospace Engineering Sciences ASEN 4018 Project Definition Document ACES Airbreathing Cold Engine Start

Transcription

1 University of Colorado Department of Aerospace Engineering Sciences ASEN 4018 Project Definition Document ACES Airbreathing Cold Engine Start Monday 18 th September, 2017 Approvals Name Affiliation Approved Date Customer Capt. Ryan Petrie AFRL Course Coordinator Dale Lawrence CU/ AES Project Customers Name: Captain Ryan Petrie Phone: Name: Nicholas Taylor Phone: Name: Lucas Sorensen Phone: Name: Nicholas Moore Phone: Name: Matthew McKernan Phone: Name: Alex Bertman Phone: Name: Jake Harrell Phone: Team Members Name: James Nguyen Phone: Name: Tristan Isaacs Phone: Name: Alexander Johnson Phone: Name: Matthew Robak Phone: Name: TR Mitchell Phone: Name: Phone:

2 1. Problem Statement As Unmanned Aerial Systems become more popular in civilian markets while remaining integral to military and scientific operations, the versatility and performance of such devices become increasingly important. On the other hand, the engines that power these devices are inoperable in some harsh environments. These environments are often where the use of Unmanned Aerial Systems (UAS) could reap significant benefits. These engines, turbojets in particular, have difficulty starting at very cold temperatures, where the typical fuel (Jet A) freezes at 40 F. For normal operations starting from the ground, this problem can be mitigated by using external heaters to slowly heat the engine. However, in the case of a small UAS that is to be started from a high altitude environment at low temperature, this solution is not sufficient. It is of interest to the United States Air Force to enable a UAS to restart and reliably perform in cold-soak conditions present at an altitude of 30,000 feet, where the engine s functionality breaks down due to the freezing of the fuel lines and mechanical limitations of the initial design. Cold-soaking is a process by which every portion of a system is homogeneously cooled to a specific temperature. For the purpose of this project, cold-soaked has been defined as cooling the entire engine system to a temperature of 50 F before the start procedure can be attempted. The objective of this team is to take a JetCat P90-SXi and create an engineering solution that would enable it to successfully complete its start-up procedure, defined below, cold-soaked to -50 F, while aiming to limit the added mass and volume to +TBD%. Such a design would enable a UAS propelled by the aforementioned engine to be used in sub-zero conditions where the engine would normally fail. Upon completion of this project, the potential usability of the JetCat P90-SXi in cold-soak conditions would greatly increase. 2. Previous Work This project was given by the Air Force Research Laboratory (AFRL) as part of an annual national competition that recruits college project groups to investigate a given research question. The past several years have focused primarily on increasing the efficiency and thrust capabilities of the JetCat P90-SXi 1 3. This is much different than the current project goal of pushing the operational limits of the engine by attempting to start it at -50 F. Despite these differing goals, one of the main requirements for each of these projects, including the current one, is to be able to work with or around the engine control unit (ECU). The ECU is notorious for being difficult to work with, as it will shut down the engine if an unusual signal is received from the on board sensors. The company that makes the JetCat P-90 also does not typically respond to questions related to the ECU and has not been willing to work with groups in the past. Therefore to solve this issue, past groups have attempted different methods that mostly consist of building a separate ECU to bypass or replace the original. The past three projects attempted this with varying degrees of success. The project MEDUSA ( ) was tasked with converting the engine to run on methane instead of kerosene. They were the first group to attempt building an external ECU and were reasonably successful at intercepting and interpreting signals from the sensor package but struggled with controlling the engine 3 4. The next project, REAPER ( ), added a recuperator to the jet engine. This group attempted to place their own custom engine sensor board (ESB) inside the engine to replace the original sensor board but failed to integrate their own hall effect sensor, preventing the engine from functioning. They also built their own ECU from scratch in order to interpret the signals created by their ESB in a similar way to what MEDUSA had done the previous year 1 2. Last year s project, SABRE ( ), created a nozzle to provide supersonic thrust capability to the engine. They opted to utilize the engine s original ESB and simply bypass the original ECU using a their own custom built ECU. They achieved moderate success but once again had difficulties controlling the engine and overriding the commands of the original ECU 5 6. Regarding the problem at hand, cold-starting a jet engine is a relatively untested field. For cold temperatures, engines are normally preheated using a propane or electric heater. 7 However, for the purposes of re-starting an engine at high altitude, this method is too slow. By the time the engine is preheated by current methods, it will already have impacted the ground. In-air restarts generally use either a windmill restart or their starter motor to restart the jet engines 8. The temperature of the fuel in these cases is less of a concern, since the aircraft will have enough residual heat to keep the fuel above its freezing point. For these reasons the principles behind these project are relatively unexplored. 3. Specific Objectives The subsystem goals for this project are broken down into three levels of success described in Table 1 below. The third and final level of the table is representative of a complete project success as described by the primary objective. With little data provided from Jetcat Americas, the operational temperature range will have to be determined through testing the limits of the sensor package throughout the semester. Similarly, the fuel flow rate will have to be measured in order to determine a specific standard rate. Monday 18 th September, of 6

3 Level 1 Level 2 Level 3 Table 1. Levels of Success for the Jetcat AFRL Project Fuel Delivery System (FDS) Electronics Structures - The electronic system will - FDS will regulate Jet-A fuel regulate fuel flow - Compressor and turbines at the flow rate of standard and monitor the exhaust will rotate freely when cold operation when cold soaked to T BD temperature sensor and soaked to 50 F within a F. hall effect sensor, at T-VAC chamber. room temperature. - FDS will regulate and ignite Jet-A fuel at the flow rate of standard operation when cold soaked to T BD F. - FDS will regulate and ignite Jet-A fuel at the flow rate of standard operation when cold soaked to 50 F and integrated into the Jetcat system. - The electronic system will regulate fuel flow and monitor the exhaust temperature sensor and hall effect sensor, cold soaked to 50 F. - The electronic system will regulate fuel flow and monitor the exhaust temperature sensor and hall effect sensor, cold soaked to 50 F. and will be integrated into the larger Jetcat system - Structures will properly interact with, and not impede the functions of, either the FDS or electronics sub-systems when cold soaked to 50 F and integrated together. In addition to the objectives listed above, the customer has also provided scoring criteria with which competing design groups will be evaluated against one another. These include minimizing added volume and weight to the system, as well as minimizing the modification costs. While keeping these additions to a minimum helps with the final competitive score, they aren t necessarily considered clear objectives. The customer also indicated that groups should strive to restart the engine in conditions that simulate pressure at 30,000 ft, but the primary goal of this project is to focus on the temperature at this altitude. 4. Functional Requirements The FBD, shown below in Fig. 1, shows the normal operation of the unmodified engine inside the black boxes. The green borders around these boxes represent unknown modifications to allow the engine to start at 50 F. The blue arrows denote physical contact between different systems, such as for fuel and lubricant lines. The red arrows denote electrical commands from the ECU to the engine starter and fuel/lubricant pump. The purple arrows represent data being sent from the engine to the sensor package to the ECU. Figure 1. Functional Block Diagram The Mission ConOps diagram, shown below in Fig. 2, depicts the series of events which put the efforts of this project in context for its larger implications. While not the purpose of this project, a small turbojet engine capable of a cold-soaked start would be used to deploy from a larger transport aircraft. This UAS system would be deployed under the assumption that it would be able to start its engine(s) quickly enough to provide the lift necessary to avoid Monday 18 th September, of 6

4 impacting the ground. For more specifics into how the engine operates and starts in these conditions, please refer to the later project ConOps diagram. Figure 2. Mission Concept of Operations The Project ConOps diagram, shown below in Fig. 3, shows how the engine will be tested at Wright Patterson AFB. Starting at point 1, the engine package containing the turbojet, electronics, and fuel will be cooled to a temperature of 50 F. This will be followed by the initialization of any active cold temperature mitigation at point 2. Once the engine is operable, it will ignite at point 3. At point 4, the engine will continue with its start-up procedure, spinning up the turbine until it can idle. After the engine is brought to an idle, it will power down and prepare either for an immediate restart or another cold soaked restart. Figure 3. Project Concept of Operations Monday 18 th September, of 6

5 5.1. JetCat P90-SXi 5. Critical Project Elements Structures: Under the temperature constraints of this project, thermal compression and expansion is expected within the structure of the engine. These effects may prevent the turbine/compressor from rotating within the engine Sensor Board Modification: Any modifications to the sensor board will be difficult, since any changes to the sensors must not impact engine operation or communication with the ECU Budget and Logistics: JetCat no longer manufactures the P90-SXi, so ordering replacement parts may be difficult and expensive ECU Stock Electronics:The ECU does not allow the engine to start when it detects conditions such as temperature or RPM outside the standard operating range. These operating conditions are unknown because of JetCat s proprietary information protection policies. To fulfill the objectives of this project, the ECU must be operated at temperatures which might be below this range Modifications: The sensor package utilized by the ECU may contain a safeguard against user modifications. This poses a challenge for system integration should modifications to the engine or sensor package be necessary Fuel System Fuel Delivery: This engine uses Jet-A fuel, the viscosity of which will become an issue as the temperature approaches the fuel s freezing point of -40 F. Designing a solution the accommodate the increase in viscosity will be crucial for the delivery of fuel to the injector Fuel Ignition: The ignition of atomized fuel is more difficult with increased viscosity, due to larger droplet size Modeling Software: Computational verification will be necessary in order to demonstrate the feasibility of design choices. This could include computational fluid dynamics, transient thermal analysis, and CAD based FEA Physical Analog: Engine analogs will be used to verify the success of project subsystems. This alleviates the requirement of complete system integration to verify the success of individual subsystems Testing Logistics: The low temperature nature of this project necessitates finding a facility capable of cold soaking the engine to 50 F and/or allowing the engine to operate. This will be difficult because currently available Thermal Vacuum Chambers are ill-equipped to handle running jet engines. 6. Team Skills and Interests Names Lucas Sorensen Nicholas Taylor T.R. Mitchell Nicholas Moore Matthew McKernan James Nguyen Alex Johnson Matt Robak Alex Bertman Tristan Isaacs Jake Harrell Table 2. Team Skills and Interests Skills/Interests Project Management/Systems Engineering, Thermodynamics, Structures Systems Engineering, Structures, Thermodynamics Systems Engineering, Budgeting, Data Analysis, Electronics Electronics/Software, Simulation, System Integration Testing, Modeling, Structural Analysis, Systems Integration Manufacturing, Structures, Propulsion, Aerodynamics, Thermodynamics Aerodynamics, Electronics, Propulsion, Manufacturing Microavionics/Electronics, Fourier Series for Transient models Electronics, Thermodynamics, Software, Systems Engineering Aerodynamics, Thermodynamics, Structures, Manufacturing Thermodynamics, Mechanisms, Manufacturing, CAD/modeling Monday 18 th September, of 6

6 7. Resources Jetcat P90 Electronics Fuel System Modeling Testing Table 3. Resources for Critical Project Elements Matt Rhodes: Experience with the JetCat engine Bobby Hodgkinson: Experience with the JetCat engine James Nabity: Previous experience with propulsion systems and jet engines Trudy Schwartz: Experience with past projects electronics system and general knowledge of electronics and software Bobby Hodgkinson: Experience with JetCat electronics and general electronics knowldege Peter Merrick: Member of REAPER who can help with electrical and software advice James Nabity: Previous experience with propulsion systems and jet fuel properties Solidworks and CAD for fluid analysis John Evans: CFD and fluent knowledge Fluent: CFD modeling Boulder airport: Base test of the engine Thermal testing chamber Matt Rhodes: Experience running the JetCat engine References [1] Kevin Bieri, David Bright, Kevin Gomez, Kevin Horn, Becca Lidvall, Andrew Marshall, Carolyn Mason, Peter Merrick, Jacob Nickless, REAPER Project Definition Document, Sept [2] Kevin Bieri, David Bright, Kevin Gomez, Kevin Horn, Becca Lidvall, Andrew Marshall, Carolyn Mason, Peter Merrick, Jacob Nickless, REAPER Test Readiness Review, Mar [3] Ma Huikang, Daniel Frazier, Crawford Leeds, Corey Wilson, Carlos Torres, Alexander Truskowski, Christopher Jirucha, Abram Jorgenson, and Nathan Genrich, MEDUSA Project Definition Document, Sept [4] Ma Huikang, Daniel Frazier, Crawford Leeds, Corey Wilson, Carlos Torres, Alexander Truskowski, Christopher Jirucha, Abram Jorgenson, and Nathan Genrich, MEDUSA Test Readiness Review Presentation, March [5] Andrew Sanchez, Tucker Emmett, Corrina Briggs, Jared Cuteri, Grant Vincent, Alexander Muller, SABRE Project Definition Document, Sept [6] Andrew Sanchez, Tucker Emmett, Corrina Briggs, Jared Cuteri, Grant Vincent, Alexander Muller, SABRE Critical Design Review Presentation, Dec [7] Stephen Pope, Cold Weather Engine Starting, Flying Magazine, Jan [8] Flightglobal archive flight International 10 July 1982 p59 [9] Stephen Puttick, Liquid Mists and Sprays Flammable Below the Flash Point The Problem of Preventative Bases of Safety, 2008, p4. Monday 18 th September, of 6