CA2987343A1

CA2987343A1 - Natural gas engine

Info

Publication number: CA2987343A1
Application number: CA2987343A
Authority: CA
Inventors: Maoz Betzer-Zilevitch
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2019-06-01

Abstract

A method and system for improving the efficiency of a vehicle operated by a pressurized natural gas or LNG by recover the energy invested in the compression or liquefaction fuel gas while recovering heat from the combustion exhaust waste heat generated by the combustion engine in multiply pressure energy recovery stages and integrating the system into a piston engine operated in Otto or Atkinson cycle.

Description

NATURAL GAS ENGINE
Field of the Invention This application relates to a system and method that improves the overall energy efficiency of mobile units operated on pressurized or liquefied gas, in particular mobile units and vehicles operated on compressed natural gas or liquefied natural gas.
To concentrate the gas fuel significant amount of energy is invested into the gas phase to increase its pressure so significant amount can carried by the vehicle fuel tank or in liquefaction.
Typically in the prior-art this invested energy is wasted when the fuel is used as a combustion fuel. The present invention is a system and method to recover this compression invested energy with the use and recovery of additional energy from the combustion waste energy for the re-heating of the expansion fuel gas in a single stage or multiply stages. This invention will minimize the amount of fuel required to operate an internal combustion engine and by that increasing the range of the vehicle, reducing the fuel consumption and as a result, reduce the CO2 gases generated by the vehicle.
BACKGROUND OF THE INVENTION
Natural gas is used as a fuel in internal combustion motors and turbines in various types of vehicles. To maintain sufficient fuel on the mobile vehicle, the gas has to be compressed or liquefy and maintained in insulated tank. Synthetic gas with combustion properties also have to be compressed to high pressures to archive sufficient energy per volume unit.
To archive such energy concentration either by compression or liquefaction, significant amount of energy is invested into the compressed gas. This compression energy is lost in the process on both ends ¨
the compression and the decompression prior to the combustion. There is a need to recover the invested compression energy carried in the mobile vehicle tank to increase the overall efficiency that can be reflected in decreasing the fuel consumption, increasing the travel range and decreasing emissions on the mobile side.
The use of the pressurized gas is combined with the use of the flue gas combustion heat where the expanding gas is re-heated prior to expansion to increase the recovered energy during the expansion process.
Various patents have been issued that are relevant to this invention. For example:
U.S. Patent Pub. No.: US 2013/0199500 Al Published on Aug. 8, 2013 by Matos-Cuevas describes a modification of an internal combustion engine so that it can be operated using compressed air instead of fuel Canadian Patent No. 2716283, issued on July 30, 2013 to DUNN et al. describes a system for a gaseous fuelled two engine system comprising a high pressure direct injection engine as the main power source and an auxiliary fumigated engine that can be fueled with vapor removed from a storage tank that stores the gaseous fuel in liquefied form at cryogenic temperatures. The fuel supply system comprises a cryogenic pump for raising the pressure of the fuel to the injection pressure needed for the high pressure direct injection engine, and the cryogenic pump is powered by the auxiliary fumigated engine. In Dunn invention the energy invested in the liquefaction is lost.
Canadian Patent application No. 2762697, by to Melanson et al. published on June 22nd 2013 describes supplying gaseous fuel from a tender car to an internal combustion engine on a locomotive comprising storing the gaseous fuel at a cryogenic temperature in a cryogenic storage tank on the tender car; pumping the gaseous fuel to a first pressure from the cryogenic storage tank; vaporizing the gaseous fuel at the first pressure; and conveying the vaporized gaseous fuel to the internal combustion engine; whereby a pressure of the vaporized gaseous fuel is within a range between 310 bar and 575 bar.
WO 2015/159056 A3 of SEALY et. al. published 22 October 2015 describing a system for an engine comprises a heat recovery system and a gaseous fuel supply system. The heat recovery system comprises a first reservoir for fluid, at least one evaporator for transferring heat from an engine to the fluid, a vapour expander for converting fluid vapour energy into motive power, and a condenser. The gaseous fuel supply system comprises a second reservoir for liquefied gaseous fuel and a fuel evaporator for expanding liquefied gaseous fuel into gaseous fuel for the engine.
The objects and advantages of the present invention will become apparent from a reading of the attached specification, drawings and appended claims.
BRIEF SUMMARY OF THE INVENTION
The method and system of the present invention for high efficiency combustion of compressed fuel gas includes the following steps: (1) Heating pressurized fuel gas with combustion gas heat.

(2) Expanding the heated fuel gas and recovering at least a portion of the expansion energy. (3) combusting the lowered pressure fuel gas in an internal or external combustion engine to generate energy and combustion exhaust gas (4) recovering heat from the combustion gas to heat the compressed fuel gas prior to the expansion stage.
The present invention method to operate a mobile gas combustible engine with the use of pressurized fuel gas comprising the following steps: concentrating fuel gas into a container where said concentrated fuel gas is selected from a group containing:
compressed natural gas, compressed produced gas, liquefied natural gas and condensed light hydrocarbon; heating said concentrated fuel gas in heat exchanger with combustion flue gas to generate high pressure hot fuel gas; expanding said high pressure hot fuel gas while generating work energy and medium pressure fuel gas; heating said medium pressure fuel gas in heat exchanger with combustion flue gas to generate medium pressure hot fuel gas; expanding said medium pressure hot fuel gas while generating work energy and low pressure fuel gas; combusting said low pressure fuel gas in an engine to generating work energy and combusting flue gas and recovering heat from said generated hot flue combustion flue gas for heating said high pressure and medium pressure fuel gas.
The present invention system to operate a mobile gas combustible engine with the use of pressurized fuel gas comprising the following components: a combustion engine combusting low pressure fuel gas for generating work energy and combustion flue gas; a container with concentrating fuel gas where said concentrated fuel gas selected from a group containing:
compressed natural gas, compressed produced gas, liquefied natural gas and condensed light hydrocarbon; a heat exchanger in a fluid connection to said concentrating fuel gas and engine exhaust gas for heating said concentrating fuel gas for generating hot high pressure fuel gas; a high pressure expansion apparatus recovering energy from said hot high pressure fuel gas while generating medium pressure fuel gas; a heat exchanger in a fluid connection to said high pressure expansion apparatus and engine exhaust gas for heating said medium pressure fuel gas with heat from said engine exhaust gas for generating hot medium pressure fuel gas; a medium pressure expansion apparatus recovering energy from said hot medium pressure fuel gas while generating low pressure fuel gas in fluid connection to said combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic view of the current invention for a single stage expansion.
FIGURE 2 is a schematic view of the current invention for a double stages expansion.
FIGURE 3 is a schematic view of the current invention for a triple stages expansion.
FIGURE 4 is a schematic view of the current invention for a double stages expansion piston with an engine.
FIGURE 5 is another schematic view of the current invention for a double stages expansion piston with an engine.
FIGURE 6 is a schematic view of the current invention for a double stages expansion piston with compressed air vessel.
FIGURE 7 is a schematic view of the current invention for a double stages integrated combustion and expansion piston with pressurized crankcase.
FIGURE 8 is a schematic view of the current invention for an integrated V type integrated engine and expansion pistons.
FIGURE 9 is a schematic view of the current invention for a combustion engine piston that perform both the expansion cycle and the standard combustion cycle with heat exchanger and medium pressure fuel gas tank.

DETAILED DESCRIPTION OF THE INVENTION
FIGURE 1 shows an embodiment of the current invention for recovering energy from a source of a concentrated fuel gas. A pressurized or liquefies hydrocarbons like compressed natural gas or LNG is stored in vessel 3. The pressurized gas is fed into a heat exchanger /
evaporator 1 where the pressurized gas is heated with the heat from a combustion exhaust gas 12 of an internal engine or gas turbine 11. The heated gas 5 is expanded on an expander 6 with energy recover 7 to generate mechanical rotating energy that can be used to operate a vehicle through a gear system or generate electric energy that can be used for charging batteries or operate an electric motor. The expander 6 can be a turbine expander, a piston expander or any other compressed gas engine that can recover the compression gas enthalpy to a mechanical energy.
The lower pressure fuel gas 8, after portion of its energy was recovered on the expander 6, is fed into engine 11 for combustion. In the engine it is combusted with oxidizer like air 9. The air flow 9 can be at an atmospheric pressure or at high pressure with the use of turbo or supercharger. The engine 11 is a piston internal combustion engine, a wankel type engine or a gas turbine.
Heat is recovered 1 from the exhaust gas 12 generated by the engine 11. The lower temperature exhaust gas 2 is discharged from the system.
FIGURE 2 shows another embodiment of the current invention.
A pressurized or liquefies hydrocarbons like compressed natural gas, LNG or pressurized synthetic gas is stored in vessel 1. The pressurized gas 2 is fed into a heat exchanger / evaporator 7 where the pressurized gas 2 is heated with the heat from a combustion exhaust gas 11 of an internal combustion engine or gas turbine 12. The heated gas 3 is expanded on a high pressure expander 3 with energy recover 5 to generate mechanical rotating energy that can be used to operate a vehicle through a gear system or generate electric energy that can be used for charging batteries or operate an electric motor. The expander 3 can be a turbine expander, a piston expander or any other compressed gas engine that can recover the compression gas enthalpy to a mechanical energy. The lower pressure fuel gas, after portion of its enthalpy was recovered on the expander 3, is fed into a second heat exchanger 8 and heated with heat from combustion gas 11. To increase the efficiency, the heat exchangers 8 and 7 can be a counter flow heat exchangers operated in a row where the lower pressure fuel gas is heated first with the combustion flue gas 11 heat, and the higher pressure fuel gas 2 is heated second. The low pressure fuel gas is expanded on a second expander 4 to recover portion of its enthalpy in the form of a mechanical or electrical energy. The further lower pressure fuel gas 9 is mixed and combusted with air 10 to generate mechanical or electrical energy 13. The mixture and combustion can be performed in a gas turbine or internal combustion engine like piston engine or wankel type engine operating at Otto or Atkinson cycle.
FIGURE 3 shows a schematic visual illustration of the present invention.
A pressurized fuel gas like natural gas or produced gas like synthetic gas is contained in longitude pressure vessel 21. The pressure vessel can be composed from few longitudes vessels in side by side arrangement connected to a manifold. This arrangement can reduce the pressure vessels wall thickness and limit the energy stored in each unit like 21. A
compromising of one unit will only release the amount of stored energy in this particular unit, and by that limit the potential explosion risk. Liquefy natural gas or other light hydrocarbon in the form of liquid can be supplied 23 by a pump pressurizing the liquid as well. The pressurized fluid 13 is heated in a non-direct heat exchanger 11 where any liquid evaporates to gas and the gas specific weight decreases due to the increase in the gas temperature. The high pressure heated fuel gas 4 is expanded at a first stage high pressure expansion piston 1 where portion of the supplied gas 4 enthalpy is recovered in a form of mechanical energy. The fuel gas is then discharged at a medium pressure 5 toward the second expansion step. The medium pressure fuel gas 5 is heated in a heat exchanger to generate a medium pressure heated fuel gas 6. The medium pressure heated fuel gas is expanding in the second stage piston 2 where additional energy is recovered from the expanding fuel gas. The low pressure fuel gas 7 is heated with combustion heat to generate heated low pressure fuel gas 8. The heated low pressure 8 is expanding in a third stage expansion piston 3 to recover additional energy in the form of mechanical energy. The lowest fuel gas 9 is discharged from the 3111 stage piston to be used in an internal combustion engine 19.
The discharge lowest gas 9 is flow through an accumulator vessel (not shown).
It is then mixed 15 with air 16 and combusted at an internal combustion engine to recover the chemical energy within the fuel gas13. The hot exhaust gas discharged from the combustion piston can be used to operate a turbocharger (not shown) to increase the pressure of the air 16. The hot flue exhaust gas 14 is fed to the heat exchangers to heat the fuel gas during the 3 stages expansion. The combustion flue 14 can be used to operate a turbocharger to compress the intake air 16 (not shown) for the combustion piston engine. The piston engine includes at least one cylinder with reciprocating piston19. The discharged hot combustion flue gas discharged from the engine 20 and is flow through heat exchangers to heat the fuel gas 13 during its expansion and pressure reduction stages. First heat exchanger recover heat from the combustion gas to the low pressure fuel gas 7 supplied to 3rd expansion cylinder 3. Additional heat exchanger is recovering heat from the flue gas to heat the medium pressure fuel gas 5 supplied to the 2nd expansion cylinder.

Additional heat exchanger is recovering heat from the flue gas to heat the high pressure fuel gas 13 supplied to the 1nd expansion cylinder. The cold combustion flue gas is discharged 12. The heat exchangers in Fig. 3 are arranged in a serial arrangement, however any other arrangement.
Like a parallel arrangement can be used as well. Parallel arrangement will reduce the potential flow resistant of the discharged combustion flue gas 14. The work generated by the engine and the expansion stages can use to mobile a vehicle or operate an electric generator.
FIGURE 4 shows a schematic visual illustration of the present invention.
A pressurized fuel gas like natural gas is contained in pressure vessel 21.
The pressure vessel can be composed from few longitudes vessels in side by side arrangement connected to a manifold.
Another option is to store the gas in a liquid state, like LNG. For that option the storage tank 21 will be an insulated tank and the liquid supplied under pressure by a pump to the 1st heat exchanger where it is evaporated to a pressurized gas phase. The pressurized fuel gas 13 is pre-heated with heat from the second expansion piston 2 in heat exchanger 26. The low pressure fuel gas 7 discharging from the second expansion piston is cooled at the heat exchanger and its specific volume is decreased 9. This can increase the power efficiency generated by the internal combustion piston engine 19 as it allows for more fuel to be combusted at the piston engine. The high pressure fuel gas 25, after it cooled the low pressure fuel gas 8, is heated at heat exchanger 11 with heat from the engine discharged flue combustion gas 8. The heated high pressure fuel gas 4 is expanded in a first high pressure expansion cylinder 1. The medium gas pressure leaving the first small expansion cylinder 5 is heated in heat exchanger 10 with flue exhaust gas from engine 19 to generate heated medium pressure fuel gas 6. This medium pressure fuel gas 6 is expanding in the medium pressure expanding piston 2, which is larger in volume then the 1st high pressure piston due to the gas expansion with the drop in pressure. The low pressure fuel gas discharging g from the 2nd larger cylinder is fed to heat exchanger 26 to reduce the low pressure gas temperature and increase its density. The system can operate without this low pressure fuel gas cooling at heat exchanger 26. The low pressure fuel gas, after the physical energy was recovered in the two expansion stage is fed in a controlled manner to a internal combustion engine 19. The control can include a accumulator 27 to overcome the pressure changes in the fuel gas leaving the cylinder 27. Flow control device 29 can be added to control the fuel gas injected to the internal combustion engine like piston engine 19.
The low pressure controlled fuel gas 9 is mixed with air 16 from turbo charger 28. The turbo charge is design to increase the power output from the combustion piston engine 19. It is an optional design feature, and it is possible to avoid the use of turbocharger 28, where in that case the combustion air will be an a atmospheric pressured air, possibly after dust removal with the use of filter (not shown).
The combustion flue gas discharged from the engine 19 through the exhaust valve 20 is directed to first heat exchanger 10 where it heats the medium pressure fuel has 5 discharged from the first step expansion piston 1. The heated fuel gas 6 expands in the medium pressure expansion cylinder 2. The heated combustion gas then flow through heat exchanger 11 where it heats the high pressure fuel gas 13 to generate the heated high pressure fuel gas 4 before it expand in the first high pressure expansion cylinder 1. The cold combustion gas 12 is then expands in a turbo charger 28 to direct additional air 16 to the combustion engine. The turbocharger 28 is less efficient than a standard turbocharger as it is operated on a colder exhaust gas, so the amount of energy it recovers in generating flow 16 is relatively lower. A potential advantage in this configuration is improved in the heat exchangers 10 and 11 efficiency due to the fact that more enthalpy in the discharge combustion gas 14 and the slightly higher pressure due to the turbocharger 28. Turbocharger 28 should be evaluated from the extra cost perspective and might be eliminated without significant affecting the overall system performance.
Another option is avoiding heat exchanger 26. This is done by line A40 for directly connecting the supplied high pressure fuel gas 13 to heat exchanger 11 and by line A41 for directly connecting the low pressure expansion gas 7 from the medium pressure expansion cylinder 2 to 9 where it is directed to the combustion engine 19.
FIGURE 5 shows another schematic visual illustration of the present invention.
The system includes 3 blocks: Block 42 include a pressurized fuel gas like compressed natural gas. Block 41 include 2 expansion and heating stages to recover physical energy in the compressed fuel gas while generating mechanical energy and low pressure fuel gas flow. Block 41 recovers additional heat energy from the combustion flue gas heat the compressed and expanded fuel gas. Block 40 include an internal combustion engine for combustion of low pressure natural gas while recovering the chemical energy within the fuel gas while generating mechanical energy and flue gas flow.
A pressurized fuel gas like natural gas 22 is contained in pressure vessel 21.
Another option is to use a pressurized LNG 23. The fuel gas can be pre-heated with heat from the combustion engine liquid cooling fluid 52 which is circulated into heat exchanger 53 where the high pressure fuel fluid 56 is pre-heated to generate high pressure fuel gas 55. This heat recovery reduces the heat loss through the standard engine air radiator 50. To reduce the system complexity and if the heat within the glycol cooling liquid 52 is limited, it is possible to avoid the glycol pre-heating stage where the high pressure fuel fluid from the fuel vessel bypass the heat exchanger 53 and flows 54 to the combustion gas heat exchangers for the expansion process as describes in Fig. 3 and 4.

The high pressure fuel fluid 13 is heated with combustion gas heat in heat exchanger 11. The heated high pressure fuel gas 4 is expended in 1st stage high pressure expansion cylinder 1. The medium pressure fuel gas 5 released from cylinder 1 is heated in heat exchanger 10 to generate heated medium pressure fuel gas 6 that is expand in the 2nd stage medium pressure expansion cylinder 2 to recover additional enthalpy within the pressurized fuel gas into a useful mechanical energy form. The discharged low pressure fuel gas 7 is supplied 9 to an internal combustion engine. To regulate the fuel gas supplied to the engine, accumulator vessel 27 and a controller 29 can be added. The engine in block 40 is an internal combustion piston engine operates on Otto or Atkinson cycles. Air 16 is mixed with the low pressure fuel gas 9 and combusted in engine 19.
The flue gas 14 discharged from engine 19 through the discharged exhaust valve 20. The discharge gas 14 can operate a turbocharger 28 to compress air 24 and supply the compressed air 16 to the engine, while improving the engine performance. The exhaust gas 8 leaving the turbocharger 28 is supplied to heat exchanger 10. The turbocharger is an option, where without a turbocharger the exhaust hot flue gas 14 is supplied 31 to block 41 as flow 8 for heat exchanger 10. Heat exchanger 10 heats the medium pressure fuel gas 5 before it expanded in medium pressure expansion piston 2. The flue gas is then heating the high pressure fuel gas 13 before it expanded in piston 1. In one embodiment, the low pressure fuel gas discharged from the 2' stage expansion 2 is cooled in heat exchanger 26 with the high pressure gas flow before it is heated in heat exchanger 11. The low pressure cold fuel gas 7C is directed to the combustion engine block 40 where it is mixed with air and combusted. The mechanical energy generated in Block 41 and the mechanical energy generated in Block 40 by the combustion engine is combined and coupled together 30. It is also possible to generate electricity energy in both blocks 40 and 41 separately by two electricity generators or connect them together directly or through a controlled gear ratio to control the amount of low pressure fuel gas 9 generated by block 41 to fit the combustion engine block 40 requierments.
FIGURE 6 shows another schematic visual illustration of the present invention.
The system includes 3 blocks: Block 42 include a pressurized fuel gas like compressed natural gas and a pressurized oxidizer like air. Block 41 includes 2 expansion and heating stages to recover physical energy in the compressed fuel gas and compressed air with additional heat energy from the combustion flue gas heat. Block 40 includes an internal combustion engine for combustion the compressed air and fuel gas. Pressure vessel 21 includes a compressed fuel gas, like natural gas. Pressure vessel 22 includes compressed oxidizer like air.
The fuel gas 24 flows though a controller 17 that includes a check valve 26. The compressed air 23 flows through a controller 16 that includes a check valve 25. The compressed gases are mixed together 23 at a stoichiometric ratio and heated in a first heat exchanger 11 to a safe temperature lower than the auto-ignite temperature. The high pressure heated mixture 4 expands in a 1st stage high pressure expansion stage 1 where physical pressure energy is recovered without combusting the mixture.
The discharge flow of medium pressure gas mixture 5 is heated in heat exchanger 10 to a safe temperature lower than the auto ignite temperature 6 and expand in a 2nd stage expansion stage 2.
The discharged low pressure stoichiometric gas mixture 7 is fed to combustion engine through regulator 27 and intake valve 18. The engine recovers the chemical energy in the fuel and generates hot flue combustion gas 8. The combustion gas flows thorough heat exchanger 10 and 11 where portion of its energy is recovered into the compressed stoichiometric gas in 2 stages.
The cooled combustion gas is discharged 12.

FIGURE 7 shows another schematic visual illustration of the present invention.
Compressed fuel gas 2 like natural gas is maintained in a pressure vessel 1.
It is also possible to use a LNG insulated vessel and pump the LNG under pressure 2 to the first heat exchanger 3 where it will evaporate into a pressurized gas 6. The heated pressurized gas is supplied to the crank case of an internal combustion piston engine 12 during the compression or discharge stages where the fuel gas pressure pushes the cylinder when it moves upward.
When the piston reached the dead top point the fuel gas from the 12 crank case are discharges at medium pressure as they contribute portion of their enthalpy to the first high pressure expansion cylinder and are flowing 7 to heat exchanger 8 where they are heated to generate a medium pressure heated fuel gas. The medium pressure gas 9 is injected to a cylinder crank case 13 during the piston upward movement where the medium pressure compressed gas pushes the piston 14 upwards while generating mechanical energy. The low pressure fuel gas in the 2nd stage is discharge when the piston moves down from the crank case 11. The low pressure fuel gas is combusted with air at the engine, pushing pistons 15 and 14 downward in a standard Otto cycle or Atkinson cycle. In Figure 7 only 2 pistons were presented, however it is possible to use engine with more pistons that can work in additional stages or in parallel by incorporating few pistons in a single compression / expansion stage. The engine can incorporate a turbocharger 16 to recover energy from the exhaust gas 17 for compressing air 25 before the internal combustion step.
FIGURE 8 shows another schematic visual illustration of the present invention.
The figure shows a piston configuration that can be used to execute the present system and method. The engine presented is a V engine with two sections ¨ Section 1 includes the combustion pistons design to recover the chemical energy within the fuel for generating work.

Section 2 designs to recover the physical energy within the compressed fuel gas and heat recovered from the combustion gas in section 1 for generating additional work.
The pistons are connected to a central crank case 4 which is connected to the combustion cylinder 12 and combustion piston 13 and to the expansion cylinder 5 ad expansion piston 6.
The angle between the pistons is ranging form 180 degrees (a typical opposite flat engine) through 90 degrees (a typical V engine) and up to 0 degrees (which is inline engine). Heat exchanger 9 is located in close proximity to both the expansion cylinders 5 and the combustion cylinder 13. Flue gas discharge 11 is directed in heat exchange 9 to heat the expanding pressurized fuel gas 7. The colder flue gas, after portion of its energy was recovered into the pressurized fuel gas, is discharged 10. The high pressure and medium pressure fuel gas are heated on heat exchanger 9 with the combustion gas heat. View A shoes a side view. A common crank is connected to the combustion piston 17 and the expansion pistons 15 and 16. High pressure fuel gas 25 is heated in heat exchanger 22 and expands in high pressure expansion piston. The medium presser fuel gas 21, after the first expansion stage, is heated in heat exchanger 23 and the heated medium pressure gas expands in the medium pressure expansion cylinder 16. The low pressure fuel gas 18 is used as a fuel in the combustion piston 17 where the fuel gas is compressed and combusted with air in a standard Otto or Atkinson cycle. The engine can include multiple pistons working in parallel in 2 states or in serial arrangement where the expansion stage will be composed from multiply stages one after the other.
FIGURE 9 shows another embodiment of the present invention with a common expansion and combustion gas chamber. The system and method include a high pressure fuel gas tank 1, A
medium pressure accumulate gas tank 7 and a low pressure gas thank 8. The operation is composed of the following stages:
High pressure expansion: the high pressure fuel gas 2 from tank 1 flows through open valve 3 through heat exchanger 25 where it is heated by a counter flow to combustion gas 24 to become heated fuel gas 19 and through open valve 17 and intake valve 21 into chamber 27 and expands inside while pushing piston 28 and generating work.
Medium pressure discharge: After the expansion stage the medium pressure flows from cylinder 27 through intake valve 21 and open valves 17 and 4 through heat exchanger 25 in a parallel flow relation to the combustion gas 24 to generate medium temperature medium pressure flow into medium pressure vessel 7.
Medium pressure expansion: Medium pressure medium temperature fuel gas 5 flows from the medium pressure tank 7 through valve 4 through heat exchanger 25 where it is further heated and flow through valve 17 and the intake valve 21 and into cylinder 27 where it pushes piston 28.
Low pressure discharge: The low pressure fuel gas, after energy is recovered from the medium pressure expanding gas is discharged from cylinder 27 by the piston traveling upwards through the intake valve 21 and through valves 17 and 18 and through line 9 into low pressure vessel /
accumulator 8.
For the engine combustion cycle, low pressure fuel gas flowing through valve 11 and line 12 where it mixed with air 13 and flows through valve 15 and intake valve 21 where it is combusted in a standard Otto or Atkins combustion cycles. The combustion flue gas is discharged from the exhaust valve 22 and through heat exchanger 25 where it heats the pressurized fuel gas and discharged from the system 26.

Claims

Claims:

1. A method to operate a mobile gas combustible engine with the use of pressurized fuel gas comprising:
Concentrating fuel gas into a container where said concentrated fuel gas selected from a group containing: compressed natural gas, compressed produced gas, liquefied natural gas and condensed light hydrocarbon;
heating said concentrated fuel gas in heat exchanger with combustion flue gas to generate high pressure hot fuel gas;
expanding said high pressure hot fuel gas while generating work energy and medium pressure fuel gas;
heating said medium pressure fuel gas in heat exchanger with combustion flue gas to generate medium pressure hot fuel gas;
expanding said medium pressure hot fuel gas while generating work energy and low pressure fuel gas;
combusting said low pressure fuel gas in an engine to generating work energy and combusting flue gas; and recovering heat from said generated hot flue combustion flue gas for heating said high pressure and medium pressure fuel gas.

2. A system to operate a mobile gas combustible engine with the use of pressurized fuel gas comprising:

a combustion engine combusting low pressure fuel gas for generating work energy and combustion flue gas.
a container with concentrating fuel gas where said concentrated fuel gas selected from a group containing: compressed natural gas, compressed produced gas, liquefied natural gas and condensed light hydrocarbon;
a heat exchanger in a fluid connection to said concentrating fuel gas and engine exhaust gas for heating said concentrating fuel gas for generating hot high pressure fuel gas;
a high pressure expansion apparatus recovering energy from said hot high pressure fuel gas while generating medium pressure fuel gas;
a heat exchanger in a fluid connection to said high pressure expansion apparatus and engine exhaust gas for heating said medium pressure fuel gas with heat from said engine exhaust gas for generating hot medium pressure fuel gas;
a medium pressure expansion apparatus recovering energy from said hot medium pressure fuel gas while generating low pressure fuel gas in fluid connection to said combustion engine.