Modern Engineering Thermodynamics

448 CHAPTER 13: Vapor and Gas Power Cycles
13.21 Diesel Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512
13.22 Modern Prime Mover Developments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 516
13.23 Second Law Analysis of Vapor and Gas Power Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 518
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 525
13.1 BEVEZETÉSÉNEK (INTRODUCTION)
The material in this chapter embodies the heart and soul of applied thermodynamics. Because of the human
and cultural impact this technology has had on society, the materialispresentedchronologically to provide a
historical framework for its study. It is important that engineers today develop an understanding of the relative
effect the technology they create can have on society. Therefore, the normally dry technical aspects of this enormously
powerful technology have been augmented with a small amount of relevant humanistic information in
the hope of giving it an interesting perspective.
The first part of this chapter deals with vapor power cycles and their associated technology. Were it not for this
technology, the Industrial Revolution that began in the mid 18th century would not have taken place, and the
world would be a much different place today. The section begins with basic definitions of engines, machines,
and heat, then moves on to a detailed discussion of the Rankine cycle and its various attributes. The section
ends with a discussion of modern power plant thermodynamic cycles and technology.
The second part of this chapter focuses on gas power cycles. These power cycles were originally developed as an
alternative to dangerous vapor cycle engines. The Stirling, Ericsson, and Brayton cycles are external combustion
cycles, meaning that the combustion process takes place outside the prime mover. The Lenoir, Otto, and Diesel
cycles, on the other hand, are internal combustion cycles, with the combustion process taking place inside the
engine itself. Gas power cycle technology has also had a profound impact on our culture. Gas power cycles have
come to dominate portable power systems, such as automobiles, ships, trains, and airplanes. A great deal of the
petroleum imported into the United States goes to fuel the machines powered by these cycles. Part II of this
chapter covers the thermodynamics of these cycles in detail. As engineers, we are particularly concerned with
understanding how the cycle thermal efficiency depends on design variables, such as compression ratio and
combustion temperature.
13.2 PART I. ENGINES AND VAPOR POWER CYCLES
We need to start out with a clear understanding of some of the terminology we use in this chapter. By looking
at the historical roots of words like machine and engine, we discover the true meaning of our profession—
engineering.
13.2.1 What Is a Machine?
The English word machine is from the Greek word μηχανη, meaning a device consisting of interrelated parts with
separate functions. Until the mid 19th century, the terms engine and machine were used interchangeably (though
an “engine” is more than just a machine—it is an ingenious machine). These machines were normally driven by
either animal, wind, or water power and would be referred to as animal (or horse) engines, wind (or air)
engines, or water (or hydraulic) engines, respectively.
13.2.2 What Is an Engine?
The English words engine and ingenious arederivedfromthesameLatinrootwordingignere, meaning“to
create.” About AD 200 Tertullian 1 referred to a military battering ram in Latin as an ingenium or product of
genius, and soon thereafter the word ingen was used in Latin to describe all military machines (catapults,
assault towers, etc.). The Latin word ingen then became assimilated into English but its spelling was changed
to engine.
1 Quintus Septimius Florens Tertullianus (ca. AD 150–230) was an early Christian author who helped establish Latin (rather than
Greek) as the language of Christianity. He coined many new Latin words and phrases as he wrote about the moral and practical
problems facing the early Christians of his time (proper dress, military service, marriage and divorce, arts, theater, etc.).