“POLLUTION LESS ENGINE”

        

ABSTRACT

The quest of human beings to develop engines with high power, high torque, less vibration and most essentially with no pollution is on since the discovery and development of engine. Stirling engine is just one step forward towards the creation of a noise free and pollution less engine.

            The Stirling engine is the engine, which uses a fixed amount of gas sealed inside a cylinder. The expansion and contraction of the gas, using heat from external source, creates the useful work. The main advantage of this engine is its capability to use any type of fuel and the emission of no exhaust gases.

            Due to this pollution free and use of any type of fuel characteristics the Stirling engine shows a greater potential over any other type of engine existing today. To consolidate this claim an effort has been made to develop a working model of Stirling engine.

INTRODUCTION

All of us including the lamest of laymen would have at one time or another experienced problems with our vehicles engine and most of the time after moaning and cursing finally in line with the universe and accepting our doom we would have coughed up the cash for repairs and parts and insistently taken old parts home, disregarding the fact that no descent human would have wanted them and during this exercise in existence it is doubtful that anybody would have chance to miss seeing a piston or two, this ubiquitous creatures that scurry up and down in an enclosed cylindrical space, getting their crowns slammed regularly and unceremoniously…eventually to be thrown aside and replaced by a marginally wider chap. Doubtful that any of us would be able to imagine modern travel without an internal combustion cycle. Hell if we ask our mechanic if he has ever seen a vehicle without any exhaust then he is probably going to refer to you to the nearest shrink.

           So an engine without any exhaust gas is a mirage or it can be a reality? The answer for this is definitely yes. We can have an engine without any exhaust gas and that is what a Stirling engine is. 

  STIRLING ENGINE

The Stirling engine is a heat engine that is vastly different from an internal combustion engine. Stirling engines have two pistons that create a 90-degree phase angle and two different temperature spaces. The working gas in the engine is perfectly sealed, and doesn't go in and out to the atmosphere. The Stirling engine uses a Stirling cycle, which is unlike the cycles used in normal internal combustion engines.

• The gas used inside Stirling engine never leaves the engine. There are no exhaust valves that vent high-pressure gases as in petrol or diesel engine, and there are no explosions taking place.
• The Stirling cycle uses external heat source, which could be anything from gasoline to solar energy to heat produced by decaying plants. No combustion takes place inside cylinder of the engine.

TYPES OF STIRLING ENGINE

        Stirling engines can be classified as:

•   Two pistons type Stirling engine
•   Displacer type Stirling engine.

TWO PISTON TYPE STIRLING ENGINE

The two-piston type Stirling engine uses two power pistons. Out of the two pistons one is hot piston, which is used in hot chamber, and the other one is a cold piston used in cold chamber. The space above a hot piston is always heated by a heat source. The space above a cold piston is cooled always by cold air.

                                              

DISPLACER TYPE STIRLING ENGINE

The displacer type Stirling engine uses a power piston and a displacer. The space below a displacer piston is always heated by a heat source. The space above the displacer piston is cooled always by cold air. The displacer piston displaces hot air and cold air.

PARTS OF A STIRLING ENGINE

Main chamber: It is the chamber where a fixed amount of gas is sealed initially. Inside this chamber only expansion and compression of gas takes place.

Output Shaft: It is horizontal and mounted several inches above the main chamber. The end of shaft centered over the main chamber has a crank and connecting rod, which drives the displacer.

Displacer:  This is the large piston in the drawing. This piston is very loose in its cylinder, so air can move easily between the heated and cooled sections of the engine as the piston moves up and down.

Power piston: This is the smaller piston at the top of the engine. It is a tightly sealed piston that moves up as the gas inside the engine expands.

Crankshaft: The crankshaft is made up of steel, which passes through the bearing and receives the crank disc .the crank disc forms mount for flywheel.

Regenerator: The regenerator is constructed of material that readily conducts heat and has a high surface area. When hot gas is transferred to the cool cylinder, it is first driven through the regenerator, where a portion of the heat is deposited.  When the cool gas is transferred back, this heat is reclaimed; thus the regenerator "pre heats" and "pre cools" the working gas, dramatically improving efficiency.

STIRLING CYCLE

            The key principle of Stirling engine is that a fixed amount of gas is sealed inside

the engine. The Stirling cycle involves a series of events that change the pressure of gas inside the engine, causing it to work.

           Stirling engine uses two cylinders, one cylinder is heated by an external heat source and the other is cooled by an external cooling source. A linkage that determines how they will move in relation one another connects the gas chambers of the two cylinders to each other mechanically.

Expansion: At this point, most of the gas in the system has just been driven into the hot cylinder.  The gas heats and expands driving both pistons inward.

Transfer: At this point, the gas has expanded. Most of the gas (about 2/3rds) is still located in the hot cylinder.  Flywheel momentum carries the crankshaft the next 90 degrees, transferring the bulk of the gas to the cool cylinder.

Contraction: Now the majority of the expanded gas has been shifted to the cool cylinder.  It cools and contracts, drawing both pistons outward. 

Transfer: The now contracted gas is still located in the cool cylinder.  Flywheel momentum carries the crank another 90 degrees, transferring the gas to back to the hot cylinder to complete the cycle.

The Stirling engine only makes power during the first part of the cycle. There are two main ways to increase the power output of a Stirling cycle.

Ä  Increase power output in stage one: In part one of the cycle; the pressure of heated gas pushing against the piston performs work. Increasing the pressure during this part of the cycle will increase the power output of the engine .one way of increasing the pressure is by increasing the temperature of the gas.

Ä  Decrease power usage in stage three: In parts three of the cycle; the piston performs work on the gas, using some of the power produced in the part one, lowering the pressure during this stage of the cycle thus effectively increasing the power output of the engine. One way to decrease the pressure is to cool the gas to a lower temperature.

ADVANTAGES

F There is no exhaust of gases as in case of normal piston engines.

F These engines are quieter in operation.

F Gas inside the engine never leaves the engine.

F The external heat source could be anything-even heat from our hand.

F No combustion takes place inside cylinder of engine. Hence there is no explosion.

RECENT APPLICATIONS

Stirling Thermal Motor

This motor uses heater tubes, combustor, and piston, to convert thermal energy into mechanical work.

 Four-Piston Wobble-Yoke Machine

This machine uses four pistons and wobbles yoke drive. This machine is especially used where high power generation is required.

Four Cylinders Free-Piston Alpha Engine

The four cylinders are physically arranged with a 90-degree phase difference with each piston connected to a gas compressor. The gas compressors are then used to drive a gas turbine expander .The main advantage of this system is the promise of a high specific power and most important, high reliability and life resulting from the absence of heavily loaded moving parts.

SUMMARY

The Stirling engine, types, parts; working cycle, advantages along with recent applications has been empounded in this paper.

            The Stirling engine is the engine, which uses the gas sealed inside the cylinder. The expansion and contraction of the gas, using heat from external source, creates the useful work. This engine can work on any type of fuel whether it is conventional or non-conventional fuel. And the basic advantage of this engine is that the amount of gas inside the chamber remains fixed that is there is no exhaust and hence this engine is pollution less.

Due to this pollution free and use of any type of fuel characteristics the Stirling engine has greater potential over any other type of engine existing today. Hence this engine is highly preferred in automobile sector finding its application in submarines to hybrid cars. Due to the above specified advantages the striling engine is giving a cutting edge to all other engine existing today and is viewed as an answer to the existing energy crisis.

REFERENCES

1. Heywood, John B.  “Internal Combustion Engine Fundamentals” McGraw-Hill, Inc., 1988.

2. Drallmeier, Jim PhD.  “Class Notes from ME 333, Internal Combustion Engines” 2003.

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