WO2016025562A1

WO2016025562A1 - External combustion engine and method

Info

Publication number: WO2016025562A1
Application number: PCT/US2015/044784
Authority: WO
Inventors: John Zajac
Original assignee: John Zajac
Priority date: 2014-08-13
Filing date: 2015-08-12
Publication date: 2016-02-18

Abstract

Positive displacement split cycle external combustion engine with a least one compression cylinder and at least one expansion cylinder wherein the swept volume of the expander is larger than the swept volume of compressor. The system includes a first heat exchanger in which the temperature and pressure of gas from the compression cylinder are further increased by heat from an external source such as the smoke stack of a biomass burning system, solar mirrors, or the burning of fossil fuels such as natural gas burned during flaring, for delivery to the expansion cylinder.

Description

EXTERNAL COMBUSTION ENGINE AND METHOD

Background of the Invention

Field of Invention

This invention pertains generally to the generation of electrical power and, more particularly, to a highly efficient external combustion engine and method of operation which are particularly suitable for use with heat from sources such as waste heat recovering systems, solar radiation, and flaring for generating electrical power that can be supplied to the grid or otherwise be used locally.

Related Art

In a world where fuel and electrical power are in limited supply, there is an ever- growing need to improve fuel efficiency and recapture as much wasted energy as possible. Heat scavenging systems today typically rely on using the exhaust heat from engines, solar collectors, or the burning of biomass, and fossil fuels to run either a Stirling engine, which is costly and very inefficient, or a Rankine cycle engine to evaporate a liquid in order to capitalize on the expansion of the liquid going from the liquid to the gas phase. Although such systems can scavenge low temperature heat, they are very inefficient in that much of the captured energy is again wasted in the latent heat of vaporization when the gas is exhausted. In addition, these systems often use turbines that are expensive and impractical for all but the largest, high temperature, dedicated power generating plants.

In recent years, efficiency has been the major concern of power generation. Internal combustion engines have had many design improvements. Hybrid systems have also increased engine efficiency by scavenging waste heat or energy from the engines themselves or from the wasted energy of braking. Many of these systems are expensive, complex, and require major complexity in retooling. There is, therefore a need for an efficient electrical generating system that uses readily available parts and technology to efficiently burn biomass, particularly in third world countries, to order to supply much needed electrical power to the population. There is also the need to more efficiently convert solar energy to electricity and to convert flaring gasses to clean electric power. Objects and Summary of the Invention

It is, in general, an object of the invention to provide a new and improved external combustion engine and method.

Another object of the invention is to provide an external combustion engine and method of the above character which are particularly suitable for use in the generation of electrical power.

Another object of the invention is to provide an external combustion engine and method of the above character which utilizes existing parts and is capable of generating several hundred kilowatts of electrical power from moderately sized biomass burning exhaust stacks or from solar radiation or from the flaring of natural gas.

These and other objects are achieved in accordance with the invention by providing a positive displacement split cycle external combustion engine having a compression cylinder with a reciprocating piston for compressing a gaseous working fluid, a first heat exchanger for heating the compressed working fluid with energy from an external source to produce high temperature gas, an expansion cylinder having a piston driven by the high temperature gas and a greater swept volume than the compression cylinder, a valving system for introducing the high temperature gas into the expansion cylinder during only a portion of the down stroke of the piston in the expansion cylinder, a second heat exchanger for cooling exhaust gas from the expansion cylinder, and means for returning cooled exhaust gas from the second heat exchanger to the compression cylinder for use in subsequent compression cycles.

Brief Description of the Drawings

Figure 1 is a schematic diagram of one embodiment of an external combustion engine according to the invention.

Figure 2 is an isometric view of a typical biomass waste burning system with which the invention can be utilized.

Figure 3 is a vertical sectional view, somewhat schematic, of a heat exchanger in the embodiment of Figure 2. Figure 4 is an enlarged, fragmentary cross-sectional view taken along line 4 - 4 in Figure 3.

Figure 5 is a schematic diagram of another embodiment of an external combustion engine according to the invention. Figure 6 is a chart illustrating the properties of gases that can be used as a working fluid in the external combustion engine of the invention.

Detailed Description

As illustrated in Figure 1 , the engine includes a compression cylinder 1 1 with a reciprocating piston 12 for compressing a gaseous working fluid, a first heat exchanger 13 for heating the working fluid, an expansion cylinder 14 with a piston 16 which is driven by the heated gas, and a second heat exchanger 17 for cooling the exhaust gas from the expansion cylinder. The working fluid is confined to a closed loop system, with the cooled exhaust gas from the second heat exchanger being returned to the compression cylinder through a return line 18 and intake manifold 19. Pistons 12 and 16 are connected to a crankshaft (not shown) for movement in concert within their respective cylinders.

The flow of working fluid into the compression cylinder is controlled by an intake valve 21 , flow between the compression cylinder and the first heat exchanger is controlled by an outlet valve 22, flow from the first heat exchanger to the expansion cylinder is controlled by an inlet valve 23, and the flow from the expansion cylinder to the second heat exchanger is controlled by an exhaust valve 24. The valves can be of any suitable design, and in one presently preferred embodiment, they are of the type shown and described in U.S. Patent 8,371 ,103. The compression cylinder typically has an effective compression ratio between 10:1 and 25:1 , and with no valves in the cylinders, the volumes of the compression and expansion cylinders are virtually zero when the pistons in them are in their top dead center (TDC) positions. The exhaust cylinder has a greater swept volume than the compression cylinder. An insulated flow line 26 extends between the outlet port of compression cylinder 1 1 and the working fluid inlet of heat exchanger 13, and the high temperature output port of heat exchanger 13 is connected to the inlet port of expansion cylinder 14 by a flow line 27 having an insulating jacket 28 which is typically fabricated of refractory material that can withstand the relatively high temperatures of the heated gas in the line. The exhaust port of expansion cylinder 14 is connected to the working fluid input of heat exchanger 17 by a flow line 29. The insulation on the inlet line to the large heat exchanger can be external because metal is not stressed at the temperatures of the working fluid in it. The external insulation is cheaper and easierto use than internal insulation. The insulation on the high temperature parts of the engine may be internal to help protect the metal from high temperature heat.

The temperature and pressure of the gas in flow lines 18, 26, 27, and 29 are monitored by temperature sensors 31 , 34 and pressure sensors 36, 39 connected to respective ones of the lines. These sensors monitor how the engine is working and provide information that controls the operation of the engine.

A starting pump 41 is connected between the intake manifold and flow line 26 for reducing the pressure in the intake manifold and pumping gas into the large heat exchanger. This will restore proper operating pressures in the engine if it has been sanding idle for a long period of time and the high-pressure gas has leaked into the intake manifold.

A vent tube 42 is connected between the crankcase 43 and intake manifold 19 for recovering any of the working fluid that may leak past the pistons and preventing the pistons from having to move against high pressure.

The engine operates on heat from an external source such as exhaust gases produced by the burning of biomass waste, heat from solar mirrors, and heat from the flaring of natural gas and other fossil fuels. As illustrated in Figure 2, a biomass waste burning system typically has one or more exhaust stacks 44 through which high temperature exhaust gases are discharged.

In the embodiment of Figure 1 , heat exchanger 13 is mounted on the exhaust stack of a biomass waste burning system, with the hot exhaust gases from the stack flowing upwardly through the heat exchanger and out through the top. The exhaust stack is typically cylindrical or round, whereas the heat exchanger is square, and, as illustrated in Figure 3, an adapter section 46 provides a smooth transition from the round stack to the square heat exchanger.

The heat exchanger has side walls 47 of refractory material that can withstand the high temperatures within the exchanger. These walls are constructed of rectangular blocks or bricks and provide a square tower or housing for the heat exchanger.

As illustrated in Figures 3 and 4, the heat exchanger typically has a plurality of tubes 49 through which the working fluid passes. These tubes extend in serpentine fashion between the upper and lower ends of the exchanger and are arranged in groups 51 , 52 that are disposed side by side. Each group has a plurality of tubes that are connected together in parallel and carry the working fluid for a given engine. The embodiment illustrated has four groups of tubes and can power four engines. As best seen in Figure 4, adjacent ones of the horizontal tubing runs 49a are offset laterally to create turbulence in the exhaust gases and thereby promote greater heat exchange between the hot exhaust gases and the working fluid. In the event that one set of tubes develops a leak, it can be shut off or be easily replaced.

The heat exchanger can be of any suitable size, and with a 40 foot high waste burning system of the type shown in Figure 2, it might, for example, have a tower height of about 15 feet, with 1/2 inch tubing having horizontal runs that are approximately 6 feet long and spaced about 6 inches apart, a 1/2 inch offset between adjacent ones of the runs, and 12 tubes in each of the groups for the different engines.

Small heat exchanger 17 is of similar construction, with a round or cylindrical side wall 17a instead of the square, refractory side wall of the large heat exchanger.

Ambient airflows upwardly through the small heat exchanger to cool the exhaust gases from the expansion cylinder.

Operation

The working fluid is drawn in to the compression cylinder during the downstroke of the compressor piston and compressed on the upstroke. During compression, the gaseous working fluid increases both in temperature and in pressure. At a predetermined point, the outlet valve is opened to allow the heated, pressurized gas to enter the tubing of the large heat exchanger. The piston pushes virtually all of the gas out of the compression cylinder since the volume of the cylinder with the piston at top dead center (TDC) is virtually zero.

The working fluid or gas moves through the heat exchanger where it is heated and expanded. The pressure within the exchanger is relatively constant since the volume of gas entering the heat exchanger multiplied by the rate of expansion due to heating within the exchanger is equal to the volume of the gas leaving the heat exchanger even though the volume of the expander is much greater than the volume of the compressor. The temperature of the high temperature gas exiting the heat exchanger is between 1 .3 and 3.5 times greater than the temperature of the compressed gas from the compression cylinder in degrees Kelvin.

The highly heated gas from the heat exchanger then enters the expansion cylinder for a specific portion of the downstroke of the expander piston. The length of time the inlet valve remains open is controlled by the system controller. It may also be a fixed time as the generator typically operates at a fixed RPM to maintain a fixed frequency (CPS). The inlet valve is preferably of the type shown and described in U.S. Patent 8,371 ,103. That type of valve provides maximum efficiency since it requires very little force to open and close, does not require water cooling which would cool the heated gasses, or require oil lubrication to operate at elevated temperatures typically in the range of 750^° C. With special materials, this temperature can be increased to the range of 1 100^° C which, in turn, allows for a higher efficiency. As the gas expands in the expansion cylinder, the temperature and pressure of the working fluid, or gas, both decrease.

The exhaust valve is opened when the expansion piston is at or near bottom dead center when the engine is at full load and opens later for partial loads. The gas is pushed out of the cylinder on the upstroke of the piston, but the exhaust valve is closed before the piston reaches TDC in order to pressurize the very small volume at TDC to be approximately equal to the operating pressure of the large heat exchanger. This causes the pressure differential between the expander cylinder and the large heat exchanger to be very small and minimizes the force required for opening the inlet valve. Reducing valve train forces and losses contribute to the high efficiency of the engine. The work of compressing this gas is not lost as it is recaptured as work done on the next downstroke.

The exhausted gas is then passed through the small heat exchanger where it is cooled to near ambient temperature, then returned to the intake manifold for use in subsequent intake and compression cycles.

The embodiment shown in Figure 5 is generally similar to the embodiment of Figure 1 , and like reference numerals designate corresponding elements in the two. In the embodiment of Figure 5, however, a large storage tank 56 is connected to exhaust line 29. The large volume prevents the buildup of high- pressure gas if the engine is shut down for an extended period. Gas leaking past valves and rings would otherwise cause damaging pressure buildup in the engine oil pan and the low pressure parts of the system.

Storage tank 56 preferably has a capacity on the order of 20 times the volume of gas between the compressor and the expander. Such a tank might, for example, have a diameter of 2.7 feet, a height of 7 feet, and a capacity of about 40 cubic feet. The tank is provided with a pressure relief valve 57 which prevents the pressure in the tank from rising above a safe level such as 100 - 125 PSI.

This embodiment also includes a pressure booster 59 such as a turbocharger or blower for increasing the pressure of the working fluid or gas delivered to compression cylinder 1 1 and an intercooler 60 between the booster and cylinder for decreasing the temperature and increasing the density of compressed gas. A temperature sensor 61 and a pressure sensor 62 for monitor the temperature and pressure in manifold 19, and a valve 63 is connected between starting pump 41 and flow line 26.

Flow line 26 is provided with an escape gas port 64 with a pressure relief valve 66, and working fluid such as nitrogen can be introduced into the flow line through an inlet 67 with a control valve 68.

Upon starting, the starting pump 41 is used to return pressure to the large high temperature heat exchanger 13. This, in turn, reduces the pressure in the storage tank 56 and readies the storage tank for use in the next extended shutdown.

Figure 5 shows the temperature and pressures when the engine is operating at a maximum temperature of 750^° C. Working Fluid

Heat scavenging systems heretofore provided typically use hydrogen or helium as the working fluid, which can present several substantial problems. First, hydrogen is an extremely combustible gas that introduces a substantial explosion and fire risk especially at the temperatures required. Secondly, both hydrogen and helium are very small molecules and, thus, leak out of most seals and even welds. Third, hydrogen can be absorbed into various metals especially at high temperatures. One advantage that these gases do have, is that the product of their specific heat and density is very low (.306 for hydrogen and .221 for helium), which means that it takes a relatively small amount of energy to raise the temperature of the gases to do useful work, thus improving efficiency.

However, a more significant property of gases for use as the working fluid in the engine of the invention is the ratio of the specific heats of the gas used, i.e., the specific heat at constant pressure divided by the specific heat at constant volume. As can be seen in the chart of Figure 6, all of the noble or inert gases (helium, neon, argon, krypton, and xenon) have a very high specific heat ratio, ranging from 1 .64 to 1 .68, and Hydrogen has a specific heat ratio of 1 .41 . Since these values are used as an exponent in common gas equations, the effect of specific heat ratios is very great, and the specific heat ratio is important in having a system that can work efficiently.

A high specific heat ratio will cause the temperature of a compressed gas to rise very quickly with respect to its pressure rise. Since the engine has a fixed maximum temperature for the heat exchanger used, and since the invention seeks to double the temperature of the gas in the heat exchanger (before consideration of thermal and pumping losses), the temperature of the compressed gas is thus also limited. Moreover, as noted above, a limited compression temperature limits the compression pressure, and since the engine uses this pressure for its work output, a limited pressure limits the amount of work the engine can produce. Thus, gases having a very high specific heat ratio are undesirable. Gases with very low specific heat ratios are also undesirable because although they can be compressed to much higher pressures while reaching the desired compression temperature, they require very high compression ratios, typically on the order of 50:1 , to reach the desired temperature and pressures. This has two disadvantages. First, there is not much volume at these compression ratios, which affects the amount of work that can be done in the expander. Secondly, since the pressure and temperature are reached only at the very end of the piston=s travel, the inlet valve has an extremely short amount of time to go from closed to open to closed. This is a very formidable problem that is addressed by the invention.

Refrigerants are either prohibited by law from being used as working fluids in heat scavenging engines or are being phased out because of concerns over damage to the ozone layer since they are hundreds or even thousands of time more damaging than carbon dioxide as a greenhouse gas. In addition, many refrigerants experience thermal breakdown at the temperatures required in the invention. There have been attempts to make refrigerants that do not contain halogens by replacing the chlorine, fluorine, and bromine in them with hydrogen. However this makes them very flammable, and using them at the temperatures utilized in the invention would create a significant fire and explosion hazard.

The engine of the invention can use a variety of gases and combinations of gases to produce high efficiency heat scavenging. However, carbon dioxide and nitrogen have been found to meet all the requirements of being thermally stable, noncorrosive, and nonflammable while having the combination of a moderate ratio of specific heats and a modest product of specific heat and density. The specific heat ratio of carbon dioxide is 1 .28 which is believed to be just a bit low since it would require a higher compression ratio to create the desired temperature and pressure, and with the higher compression ratio, the opening time of the output valve would be very short and difficult to provide. When cooling losses are factored in, the compression ratio of specific heats is reduced, which reduces the temperature of the compressed gas. To compensate for the thermal losses, a greater expansion is employed. The greater expansion allows the optimum pressure in the cylinder to be reached sooner. The volume of the pressurized gas is therefore greater, and the outlet valve opens sooner. Having the valve open longer makes the mechanical requirements easier to provide. Thus, with the real world need to compensate for thermal losses, carbon dioxide is almost a perfect gas for the working fluid.

Carbon Dioxide would be an ideal gas for use in the engine if its specific heats remained constant at all temperatures and pressures, however this is not the case. When considering the variations in the specific heats at the temperatures and pressures experienced in the engine of the invention, nitrogen is believed to be a better and more desirable choice than carbon dioxide.

Of course, there may also be other losses. To compensate for these, a separate gas such as nitrogen can be added. Nitrogen is inexpensive, thermally stable, non toxic, nonflammable, and has a modest 1 .4 ratio of specific heats which is a slightly higher that of carbon dioxide. Adding nitrogen to the carbon dioxide allows fine tuning of the operation of the engine to maximize the temperatures and pressures in the compressor to allow for a very safe and efficient expansion in the expander. The external combustion engine can be optimized for the maximum temperature of heat exchanger and provide a highly efficient power source.

Other suitable working fluids include carbon and/or nitrogen in combination with one or more noble or inert gases, i.e., helium, neon, argon, krypton, and/or xenon. As noted above, the noble or inert gases have a relatively high specific heat ratio, ranging from 1 .64 to 1 .68.

Temperature and Pressure

Practical limitations of the maximum temperature at which the large heat exchanger can operate limits the maximum temperature to which the compressed gas can be heated. The materials of which the heat exchanger is constructed must be able to withstand high temperatures and pressures for thousand of hours without creep, cracking, or failure. Reasonably priced refectories can be used at temperatures in the range of 1 ,000^° C to 1 ,150^° C. Higher priced materials such as plated tungsten and platinum can operate at much higher temperatures and thus produce higher efficiencies, but at substantially greater cost. Even lower cost materials can safely operate at temperatures in the range of 750^° C. In the engine of the invention, gas is compressed to a specific temperature and pressure, then increased in temperature and pressure in the heat exchanger, and then expanded in the expander.

To maximize efficiency, it has been found that the rate of expansion should be approximately doubled by the heat in the large heat exchanger. If the expansion is too low, little heat is absorbed by the large heat exchanger, reducing work output. If the expansion is too great, then the temperature of compression must be low, and the working pressure in the engine is also low. The low pressure coupled with the extra heat necessary to achieve the extra expansion causes both power output and efficiency to be low.

In the engine of the invention, the temperature of the exhaust is directly related to the amount of expansion. Without consideration of thermal and pumping losses, the exhaust temperature of the engine will be proportional to the product of the intake temperature and the rate of expansion. Thus, for example, if the engine takes in air at 300^° K and has an expansion ratio of 2:1 then the temperature of the gas leaving the expander would be 600^° K. This temperature may not be ideal, but it is still very useful because it is lower than the temperature in most comparable engines, which helps to keep the efficiency high. In comparison, an expansion of 3:1 would require twice as much heat to be supplied by the large heat exchanger and would produce an undesirably high exhaust temperature of about 900^° K at the output of the expansion cylinder, which is about that of a diesel engine. In addition, the high expansion requires a low compression temperature which, in turn, requires that the compression pressure also be low. The low pressure limits the work output that can be achieved, thus limiting the mechanical efficiency (HP output per engine size) as well as the thermal efficiency of the engine.

When engine losses are taken into consideration, the actual expansion ratio must be higher than 2:1 in order to have an effective expansion ratio of 2:1 , and with a nitrogen working fluid and an engine of the type shown, the actual expansion ratio may be on the order of 2.75:1 . The effective expansion ratio of 2:1 works well with a 6-cylinder engine where two cylinders are used for compression and four are used for expansion. With different gases and a different choice of maximum temperature and operation pressures, the optimum expansion ratio will be different. Engines with other numbers of cylinders can also be used. An eight cylinder engine, for example, can have two compressors and six expander cylinders if a blower or turbocharger is used to increase the pumping of the compressor by about 50%. With this boost in pressure, the two compressors produce roughly the same output as three compression cylinders without the boost, thereby maintaining an overall expansion of 2:1 . The amount of boost can, of course, be adjusted to compensate for thermal and pumping losses.

Since the engine uses a closed loop working fluid system, the input pressure can be increased, e.g., by adding more gas to the system. This would require more heat input to the heat exchanger and result in a greater power density, i.e., more output power per cubic inch of displacement.

While the inlet valve is preferably a variable timing valve, the compressor valves and the exhaust valve can be fixed timing valves if the heat source temperature and power generation are constant. The compressor valves can, for example, be reed valves that open when there is a pressure differential in the correct direction and close with the pressure differential is in the incorrect direction.

The design of the engine lends itself to being used with standard internal combustion engine parts, making implementation of the engine faster and less expensive than having to fabricate new and untested parts. If desired, waste heat from the large heat exchanger can be utilized in other engines such as a Rankine cycle engine.

It is apparent from the foregoing that a new and improved external combustion engine and method of operation have been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.

Claims

1 . A positive displacement split cycle external combustion engine, comprising: a compression cylinder with a reciprocating piston for compressing a gaseous working fluid, a first heat exchanger for heating the compressed working fluid with energy from an external source to produce high temperature gas, an expansion cylinder having a piston driven by the high temperature gas and a greater swept volume than the compression cylinder, a valving system for introducing the high temperature gas into the expansion cylinder during only a portion of the down stroke of the piston in the expansion cylinder, a second heat exchanger for cooling exhaust gas from the expansion cylinder, and means for returning cooled exhaust gas from the second heat exchanger to the compression cylinder for use in subsequent compression cycles.

2. The external combustion engine of Claim 1 wherein the majority of the working fluid is nitrogen.

3. The external combustion engine of Claim 1 wherein the majority of the working fluid is carbon dioxide.

4. The external combustion engine of Claim 1 where the working fluid is primarily a combination of a first gas having a low specific heat ratio of approximately 1 .28 and a second gas having a modest specific heat ratio of approximately 1 .40.

5. The external combustion engine of Claim 4 wherein the first gas is carbon dioxide and the second gas is nitrogen.

6. The external combustion engine of Claim 1 wherein the working fluid is primarily a combination of a gas having a low specific heat ratio of about 1 .28 and an inert gas having a high specific heat ratio of about 1 .64 to about 1 .68.

7. The external combustion engine of Claim 6 wherein the working fluid is primarily a combination of carbon dioxide and an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon, and combinations thereof.

8. The external combustion engine of Claim 1 wherein the working fluid is primarily a combination of a gas having a modest specific heat ratio of about 1 .40 and an inert gas having a high specific heat ratio of about 1 .64 to about 1 .68.

9. The external combustion engine of Claim 8 wherein the working fluid is primarily a combination of nitrogen and an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon, and combinations thereof.

10. The external combustion engine of Claim 1 wherein the expansion cylinder includes an exhaust valve that closes before the piston reaches top dead center and the pressure in the cylinder is approximately equal to the pressure in the first heat exchanger in order to reduce the pressure differential between the first heat exchanger and the expansion cylinder and thereby reduce the work required to open a valve between them.

1 1 . The external combustion engine of Claim 1 wherein the volume of the compression cylinder is virtually zero when the piston in the compression cylinder is in a top dead center position.

12. The external combustion engine of Claim 1 wherein the compression cylinder has an effective compression ratio between 10:1 and 25:1

13. The external combustion engine of Claim 1 wherein the temperature of the high temperature gas exiting the first heat exchanger is between 1 .3 and 3.5 times greater than the temperature of the compressed gas from the compression cylinder in degrees Kelvin.

14. The external combustion engine of Claim 1 including a pressure booster for increasing the flow of gas through the engine.

15. The external combustion engine of Claim 14 including an intercooler for decreasing the temperature and increasing the density of compressed gas from the booster.

16. The external combustion engine of Claim 1 including a pressure booster for increasing the pressure of the working fluid supplied to the compression cylinder.

17 The external combustion engine of claim 16 that uses an intercooler for decreasing the temperature and increasing the density of the working fluid supplied to the compression cylinder.

18. The external combustion engine of Claim 1 including a storage tank for storing gas that leaks past piston rings and valves to prevent harmful pressure buildup in the oil pan and other low pressure parts of the engine.

19. The external combustion engine of Claim 1 including means for applying hot gases from a biomass waste burning system to the first heat exchanger to heat the compressed working fluid.

20. The external combustion engine of Claim 1 including means for applying heat from solar mirrors to the first heat exchanger to heat the compressed working fluid.

21 . The external combustion engine of Claim 1 including means for applying heat from the flaring of natural gas and/or other fossil fuels to the first heat exchanger to heat the compressed working fluid.

22. A method of operating an external combustion engine, comprising the steps of compressing a working fluid in a compression cylinder, introducing the compressed working fluid into a first heat exchanger, heating the compressed working fluid in the first heat exchanger with energy from an external source to produce high temperature gas, introducing the high temperature gas into an expansion cylinder during only a portion of the down stroke of a piston in the expansion cylinder, cooling exhaust gas from the expansion cylinder in a second heat exchanger, and returning cooled exhaust gas from the second heat exchanger to the compression cylinder for use in subsequent compression cycles.

23. The method of Claim 22 wherein the working fluid consists primarily of a gas selected from the group consisting of carbon dioxide, nitrogen, helium, neon, argon, krypton, xenon, and combinations thereof.

24. The method of Claim 22 wherein the working fluid consists primarily of carbon dioxide and/or nitrogen.

25. The method of Claim 22 wherein the temperature of the high temperature gas exiting the first heat exchanger is between 1 .3 and 3.5 times greater than the temperature of the compressed gas from the compression cylinder in degrees Kelvin.

26. The method of Claim 22 including the step of boosting the pressure of the working fluid to increase the flow of gas through the engine.

27. The method of Claim 26 including the step of decreasing the temperature and increasing the density of the working fluid supplied to the compression cylinder..

28. The method of Claim 22 including the step of storing gas that leaks past piston rings and valves to prevent harmful pressure buildup in the oil pan and other low pressure parts of the engine.

29. The method of Claim 22 including the step of applying hot gases from a biomass waste burning system to the first heat exchanger to heat the compressed working fluid.

30. The method of Claim 22 including the step of applying heat from solar mirrors to the first heat exchanger to heat the compressed working fluid.

31 . The method of Claim 22 including the step of applying heat from the flaring of natural gas and/or other fossil fuels to the first heat exchanger to heat the compressed working fluid.