16.50 Introduction to Propulsion
Systems
SPRING 2001
Jack L. Kerrebrock
Introduction
These lecture notes are
offered as an aid to the students' comprehension of the subject of aerospace
propulsion. They are not meant to
replace textbooks, a pair of which are suggested for additional reading. Rather they are intended to relieve you of
the task of transcribing the lectures.
Hopefully this will enable you to follow the logic of the presentation
in real time, perhaps to contribute to its development. This should contribute
to Interactive Learning, a currently highlighted priority of the Department. I
believe that such Interactive Learning will be enhanced, and the educational
process will be more enjoyable, if you have reviewed the notes before class,
and are thus able to focus on clarifying the points that are most difficult for
you to follow. Understanding the limitations on your time, I nevertheless
believe that such a review will prove efficient for you.
The intent of the remainder
of this Introduction, is to outline very briefly the technical rationale of the
Subject, and its pedagogical structure.
We begin with the former.
Subject Content and
Rationale
This subject treats
aerospace propulsion systems of all kinds, from civil turbofans to space craft
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 of 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. In the portion of the subject devoted to
aircraft propulsion, aircraft turbine engines are discussed, both those primarily
suitable for military aircraft and those for commercial transports. For lack of
time, very velocity air breathing propulsion is not discussed.
The primary objectives of
the subject are:
• To introduce you to the
methods of Mathematical Modeling of propulsion systems and
• To use these modeling
techniques to develop an understanding of the characteristics of the several
types of propulsion system treated.
The modeling uses
thermodynamic arguments based in 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. In my view, such developments are somewhat
abstract and lacking in physical substance, in that they do not connect the
behavior of the devices to their geometry.
With lesser emphasis because
of the time limits of a single-semester subject, the mechanical or structural
aspects of propulsion devices are also touched upon, as are such issues as cost
and environmental effects. It is felt
that some understanding of such aspects of the systems is essential to provide
context for the more extensive thermodynamic and fluid mechanical developments.
Pedagogical Structure of
the Subject
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 not discussed for their
own sake, appealing as that can be.
Rather they are used as logical tools to the understanding of the behavior
of the propulsion systems. As systems, the propulsion devices must satisfy
well-defined requirements, and their performance is measured by equally
well-defined criteria. These include
the traditional measures of thrust/mass and specific fuel consumption but also
the 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.
Homework, Quizzes and
Grading
Homework will be assigned
regularly. In general it should be
completed and turned in one week from the day it is issued. This 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 can not be
covered within the time constraints of the lectures.
As we have the good fortune
to have the assistance of Mr. Vincent ----------- this year, the homework will
be graded and returned to you promptly, with sample solutions, so that there
will be an opportunity for us to correct
any misunderstandings in a timely way. I will endeavor to be available
for this purpose as much as possible. In general I will be available on class
days, MWF, but not on Tuesday or Thursday.
One mid-term quiz and a
3-hour final will count for approximately 60 percent of the final grade in the
subject, the split between the two being 20/40. The homework will count for the remaining 40 percent. Both
examinations will be open-book, open-notes, hopefully "open mind".
To stimulate your timely
attention to the homework, homework submitted later than one class after that
at which it is due, will be devaluated by 1/2. After this the homework will be
graded and returned, but will garner no credit in the above accounting.
Where You Can Find Us
Jack L. Kerrebrock Vincent Blateau
Room 31-268 blateau@mit.edu
kerbrock@mit.edu