COZBY ENTERPRISES, INC.

STEAM   ENGINES —
TWO DIVERGENT SYSTEMS
and
TWO  DIVERGENT  APPROACHES
John A. Cozby
December 17, 2013

     To the average person, a steam engine is an engine which uses steam, with little distinction between the several different types of steam engine.  There are basically two different systems and two different approaches to steam engines.  The different systems and the different approaches have to do with how the steam is utilized in a given engine.  There are also subdivisions in each category which are significant and differentiate certain aspects of the differing systems and approaches.  The subject of steam engines is more complex than the average person may realize.

     SYSTEMS:
     There are two distinct types of steam cycle systems.  The first and simplest type is an open cycle system without condensing.  The second type is a closed loop cycle system which condenses the exhausted steam back to liquid.  These engines are referred to as condensing engines.  The condensed liquid is retained to be reused for boiler feed water.  The closed loop cycle system may operate at atmospheric pressure or it may operate with vacuum. 

 THE OPEN CYCLE SYSTEM:
 In the open cycle system the engine exhausts to the atmosphere.  The exhaust steam is not captured or returned to the boiler.  The railroad locomotive is an example of the open cycle system.  The engine always exhausts against atmospheric pressure.  In certain applications where the exhaust steam is used for heating or process applications, the engine may be exhausting against pressure above atmospheric pressure.  The early Locomobile and Stanley Steamer automobiles used open cycle systems.  The open cycle system requires large quantities of make-up boiler feedwater.    Stanley later converted to the closed loop cycle system.

THE VACUUM TYPE CLOSED LOOP CYCLE SYSTEM: 
In the vacuum type closed loop cycle system the engine exhausts into an apparatus consisting of a sealed exhaust pipe, condenser, and water reservoir which separates the steam and water from the atmosphere.  A vacuum pump is employed.  The steam and water are called the working fluid.  The condensed steam (water) is then returned to the boiler to again be heated into steam and reused in the engine.  The exhaust pressure can be maintained below that of the atmosphere.  Steam power plants use a vacuum type closed loop cycle system with very low exhaust pressures.  By way of illustration, the common household refrigerator is also a closed loop cycle system.  This type of system is called a closed loop system because the working fluid is retained and reused in a continual loop.  The Rankine cycle is a closed loop steam cycle.  The Department of Energy publication, “An Assessment of the Technology of Rankine Engines For Automobiles”, is a study of condensing steam engines for cars.

      APPROACHES:
     There are two distinct approaches to steam engine design.  The first approach is a simple, single stage engine.  In such engines, steam is admitted to the cylinder, does work, and is then exhausted.
The second approach is a multi-stage engine with reheating of the steam between the stages.  The steam is admitted to the first stage, does work, is exhausted into a reheater, is then admitted to the next stage to do more work, and so on.  The engine may have two, three, or four stages with one, two, or three reheats.

 THE SIMPLE, SINGLE STAGE ENGINE:
     Most railroad locomotives are of the simple, single stage type.  The simple, single stage engine can be very powerful, can do a lot of work, and can start under load.  The railroad locomotive was a practical application of such engines.  Such engines require a great amount of steam to operate, and their efficiency is poor.  The poor efficiency of simple, single stage engines is primarily due to the single stage engine’s very limited ability in expanding the steam before the steam is exhausted.  The Department of Energy’s “An Assessment of the Technology of Rankine Engines For Automobiles”, focuses mainly on simple, single stage engines.  The reason the Department of Energy killed steam engine research was because of the poor efficiency of the simple, single stage engines.  This approach uses a lot of steam, but with little expansion, which is not efficient.

THE MULTI-STAGE, REHEATING ENGINE:
     Modern steam power plants use multi-stage, reheating systems and are very efficient.  There have been numerous multi-stage, reheating steam engines that have given good service and were of good efficiency.  The primary reason that multi-stage, reheating steam systems have good efficiency is that they can expand the steam to a much greater degree than the simple, single stage engine.  Frank D. Graham noted: “. . . an ordinary slide valve (single cylinder) engine requires about 60 lbs. feed water per horse power hour; whereas a triple expansion (three stage) engine will do the work on 1/3 or less feed water. . .”, showing the better efficiency of the multi-stage engine.  This approach uses less steam, but with greater expansion, which gives better efficiency.  The Department of Energy also recognized that a multi-stage, reheating engine could get better efficiency than the simple, single stage engine.  The Department of Energy called the multi-stage, reheating engine design an advanced Rankine cycle engine and stated that such an engine was for future development.  However, no development of multi-stage, reheating engines was done. This is the reason that the Cozby Project 2013, Steam Jeep-Green Car development effort was begun.

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