Course Meeting Times
Lectures: 3 sessions / week, 1 hour / session
Course Description
This course presents aerospace propulsive devices as systems, with functional requirements and engineering and environmental limitations along with requirements and limitations that constrain design choices. Both air-breathing and rocket engines are covered, at a level which enables rational integration of the propulsive system into an overall vehicle design. Mission analysis, fundamental performance relations, and exemplary design solutions are presented.
Prerequisites
16.50 Introduction to Propulsion Systems has 16.004 Unified Engineering IV or 2.005 Thermal-Fluids Engineering I as a prerequisite.
Acknowledgement
The class guide and objectives are courtesy of Dr. Alan Epstein and Dr. Edward Greitzer.
Learning Objectives
- List and explain the characteristics and performance of aerospace propulsion systems.
- Model newly-conceived rocket or air breathing propulsion systems and estimate their performance and behavior.
- Carry out preliminary designs of rocket or air breathing propulsion systems to meet specified requirements.
Measurable Outcomes
- Explain the different features and capabilities of chemical and non-chemical rocket propulsion systems.
- Calculate the specific impulse and mass flow for a rocket engine with the fluid considered as an ideal gas with constant specific heats.
- Estimate the specific impulse and mass flow for a rocket engine accounting for chemical reaction and non-constant specific heats.
- Explain the causes of, and estimate, the stress on rocket casings, turbomachine blades, and blade disks in turbomachines.
- Estimate the heat transfer rates in rocket nozzles and in aeroengine turbine components.
- Explain the different performance metrics, and the corresponding performance limits, for gas turbine aeroengines and link these to the design features.
- Explain the physical constraints which couple the different components in a gas turbine.
- Calculate the design thrust and overall efficiency of turbojet and turbofan engines, with and without afterburners, from given component performance.
- Calculate pressure and temperature changes across the turbomachinery, inlet, and exhaust nozzle in a gas turbine engine from a knowledge of the geometry.
- Explain the limits imposed on gas turbine engine design by environmental restrictions.
Course Materials
Recommended Texts
Kerrebrock, J. L. Aircraft Engines and Gas Turbines. 2nd ed. MIT Press, 1992. ISBN: 9780262111621.
Sutton, G. P., and O. Biblarz. Rocket Propulsion Elements. 7th ed. Wiley Interscience, 2000. ISBN: 9780471326427. [Preview with Google Books]
Lecture Notes
Lecture notes are offered as an aid to students’ comprehension of the subject of aerospace propulsion. They are not meant to replace textbooks, a pair of which is strongly suggested for additional reading.
Subject Content and Rationale
This subject treats aerospace propulsion systems of all kinds, from civil turbofans to spacecraft thrusters. Its intent is to foster an understanding of the characteristics of these diverse propulsion systems from the basic principles, showing how each uses sources of propulsive mass and energy to produce thrust.
The subject is divided into two roughly equal parts, the first covering rocket propulsion and the second aircraft propulsion. In the portion devoted to rocket propulsion, two classes of propulsion systems are considered: chemical, in which the propulsive mass and energy are combined in chemical propellants, and electrical, in which the propulsive mass is separate from the energy source, which may be either nuclear or solar. Emphasis is on chemical propulsion. In the portion of the subject devoted to aircraft propulsion, aircraft turbine engines are discussed, both those primarily suitable for military aircraft and commercial transport. For lack of time, very high velocity (hypersonic) air breathing propulsion is not discussed.
As reflected in the learning objectives, a goal is to introduce you to the methods of mathematical modeling of propulsion systems and then to use these modeling techniques to develop an understanding of the characteristics of the several types of propulsion systems treated.
The modeling uses thermodynamic arguments based on the First and Second Laws, and fluid mechanical principles that enable the linking of the thermodynamic behavior to the geometry of the propulsion devices. In this respect the subject goes considerably beyond most introductory treatments of propulsion, which usually limit the logic to thermodynamic arguments. Such developments can be somewhat abstract and lacking in physical substance in that they do not connect the behavior of the devices to their geometry.
Because of the time limits of a single-semester subject, the mechanical or structural aspects of propulsion devices are touched upon with less emphasis, as are such issues as cost and environmental effects. Some understanding of these aspects of the systems is essential to provide context for the more extensive thermodynamic and fluid mechanical developments.
Pedagogical Structure
This subject presents propulsion devices as systems, through mainly two modeling structures, one thermodynamic, the other fluid mechanical. It is important that these logical structures are employed to describe the behavior of the propulsion devices as complete systems. The disciplines are used as logical tools to understanding the behavior of the propulsion systems. As systems, the propulsion devices must satisfy well-defined requirements, and their performance measured by equally well-defined criteria. These include the traditional measures of thrust/mass and specific fuel consumption but also the (currently) less easily quantifiable measures of cost, durability, operability and environmental impact. All of these are referred to, with varying degrees of emphasis.
As noted, the subject is divided into two main parts, aircraft engines and rockets. To the extent that thermodynamic and fluid mechanical arguments span both of these classes of systems, they are developed for one but not both. Thus for example, the understanding of the behavior of exhaust nozzles, developed mainly for rockets, is assumed to be applicable to aircraft engines. The understanding of compressible channel flow, including the effect of chemical reactions, is developed mainly in the context of rockets, but is equally applicable to aircraft engines, while turbomachinery is treated primarily in the context of aircraft engines.
Grading
The grade is determined from 10 problem sets, a midterm quiz and a comprehensive final quiz. Both examinations will be open-book, open-notes.
| ACTIVITIES | PERCENTAGES |
|---|---|
| Homework | 40% |
| Mid-term Quiz | 30% |
| Final Quiz | 30% |
Homework has two purposes:
- To provide the student with timely exercise in the use of the models developed in the lectures.
- To extend the logic in directions of importance that cannot be covered within the time constraints of the lectures.
The problem sets must, therefore, represent your own work. You may certainly discuss the sets with your fellow students but the engineering should be your own.
Calendar
| LEC # | TOPICS | KEY DATES |
|---|---|---|
| 1 | Rocket equation; gravity loss; optimum acceleration | |
| 2 | Rocket staging; range of aircraft; climb & acceleration | Homework 1 posted |
| 3 | Orbital mechanics; single force center | |
| 4 | Hyperbolic orbits; interplanetary transfer | |
| 5 | Non-chemical rockets; optimum exhaust velocity |
Homework 1 due Homework 2 posted |
| 6 | Modeling of thermal rocket engines; nozzle flow; control of mass flow | |
| 7 | Modeling of rocket nozzles; effects of nozzle area ratio | |
| 8 | Types of nozzles; connection of flow to nozzle shape |
Homework 2 due Homework 3 posted |
| 9 | Solid propellant gas generators; stability; grain designs | |
| 10 | Models for rocket engines; flow of reacting gases | |
| 11 | Reacting gases (cont.); temperature dependence of specific heats |
Homework 3 due Homework 4 posted |
| 12 | Nozzle flow of reacting gases | |
| 13 | Rocket casing design; structural modeling | |
| 14 | Heat transfer and cooling |
Homework 4 due Homework 5 posted |
| 15 | Ablative cooling | |
| 16 | Thrust vectoring; engine cycles; mass estimates | |
| 17 | Aircraft propulsion, configuration and components |
Homework 5 due Optional homework posted |
| 18 | Aircraft engine modeling; turbojet engine | |
| 19 | Turbojet engines (cont.); design parameters; effect of mass flow on thrust. | |
| Mid-term quiz | ||
| 20 | Introduction to component matching and off-design operation | |
| 21 | Turbofan engines | Homework 6 posted |
| 22 | Inlets or diffusers | |
| 23 | Exhaust nozzles | |
| 24 | Compressors and fans | |
| 25 | Velocity triangles; compressor performance maps |
Homework 6 due Homework 7 posted |
| 26 | Compressor blading; design; multi-staging | |
| 27 | Turbines; stage characteristics; degree of reaction |
Homework 7 due Homework 8 posted |
| 28 | Turbine solidity; mass flow limits; blade temperature | |
| 29 | Turbine cooling; general trends and systems; internal cooling | |
| 30 | Film cooling; thermal stresses; impingement cooling; how to do cooling design |
Homework 8 due Homework 9 posted |
| 31 | Compressor-turbine matching; gas generators | |
| 32 | Engine structures; centrifugal stresses; engine arrangements | |
| 33 | Critical speeds and vibration |
Homework 9 due Homework 10 posted |
| 34 | Combustors; afterburners | |
| 35 | Pollutant; motivations for control; formation; strategies for reduction | |
| 36 | Aircraft engine noise: principles; regulations | Homework 10 due |
| 37 | Jet noise, turbomachinery noise | |
| 38 | Rotordynamics of the jet engine | |
| Final quiz |
