EP1064344A1 - Supercritical water fuel composition and combustion system - Google Patents
Supercritical water fuel composition and combustion systemInfo
- Publication number
- EP1064344A1 EP1064344A1 EP98967072A EP98967072A EP1064344A1 EP 1064344 A1 EP1064344 A1 EP 1064344A1 EP 98967072 A EP98967072 A EP 98967072A EP 98967072 A EP98967072 A EP 98967072A EP 1064344 A1 EP1064344 A1 EP 1064344A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- mixture
- fuel
- water
- engine
- injector
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- Y02T10/121—
-
- Y02T10/32—
Definitions
- This invention relates to a combustion system and more particularly to a combustion system utilizing a supercritical water/fuel composition.
- Engine manufacturers are going to higher tolerances on the piston - wall machining to reduce engine oil burning. Additionally, they are moving to higher and higher injection pressures. The higher pressures result in better spray penetration into the combustion zone as well as finer droplet sizes. The higher pressures permit smaller orifices at the injector tips while still maintaining the same mass flow rate.
- the droplet size is reduced but the droplet dimensions are still in the 1 - 10 micron range.
- a droplet size reduction by a factor of two would necessarily be accompanied by an increase in droplet number by a factor of eight from a mass balance perspective. This is important because many small droplets improve the microscopic homogeneity and reduce particulate matter production.
- the droplet size reduction at these extreme pressures is less than a factor of two over the standard 3800 psi systems.
- a 2 micron diameter droplet occupies 3 x 10 "12 cm 3 and one mole of diesel fuel occupies 300 cm 3 . Therefore, this size droplet still contains 10 "14 moles of fuel molecules, or 6 x 10 +9 molecules. It is clear that even these smaller droplets still present a challenge to completely evaporate and combust. An additional mechanism beyond pressure increases must be found.
- droplet size is primarily related to the surface tension of the fluid. Therefore, any process that reduces the surface tension can potentially reduce the droplet size.
- a chemical approach to droplet size reduction can be found in surfactant technology. Surface tension reducing additives have been applied, but their efficacy has been limited by high cost. Clearly, other chemical approaches are called for.
- addition of heat to a hydrocarbon fuel reduces its surface tension. Thus, preheating of the fuel has some appeal from both an emissions and fuel economy perspective. In practice however, heating leads to premature reformulation of the fuels into higher as well as lower molecular weight compounds. The fuel's viscosity increases at a rate that outpaces the drop in surface tension and a sticky, tarry residue is produced.
- H 2 provides cetane enhancement as it possesses a wider flammability limit.
- H 2 gas in limited quantities has beneficial qualities, because the wider flammability limits can ignite at lower oxygen concentrations.
- the invention is a composition of matter comprising a mixture of 5-70% water and a hydrocarbon and preferably 5-50% water and more preerably 20-40% water for engine applications wherein the water/hydrocarbon mixture is near or above the critical point such that the mixture is a homogeneous single phase.
- Lower amounts of water are preferable for engines and higher amounts of water are preferable for burners and combustors.
- the mixture is in the temperature range 350-500°C and preferably in the range 350-400°C and a pressure in the range 3000-6000psi and preferably in the range of 3000-4000psi.
- the invention is a fuel system including structure containing a water/hydrocarbon fuel mixture near or above the critical point such that the mixture is a homogeneous single phase.
- Structure is provided for delivering the mixture for combustion.
- Combustion may be in an internal combustion engine, turbine engine or other burner.
- an injector is provided for delivering the mixture into an internal combustion engine, either a spark ignition engine or a diesel-type engine. It is preferred that the injector be controlled electrically through a magnetically actuated armature adapted to open an injection port based on engine crank angle.
- the mixture In order for the water/fuel mixture to be near its critical point, the mixture is maintained at approximately 400°C and at a pressure of approximately 4000psi.
- the high pressure is provided preferably by a dual piston metering pump and the injector is maintained at the approximately 400°C utilizing a heat pipe to transfer heat from the exhaust manifold of the engine.
- Auxiliary electric heaters may also be provided. Because the water/hydrocarbon fuel mixture is maintained as a homogeneous isotropic single phase it will combust more completely when introduced into a combustion chamber. More complete burning takes place because liquid droplets are eliminated. The improved burning reduces particulate matter formation. The more homogeneous dispersion of fuel molecules in air results in lower nitrous oxide emissions and nitrous oxides are further reduced by the lack of droplet surface catalysis of reaction pathways. The faster, more complete combustion cycle also lowers emissions of carbon monoxide, unburned hydrocarbons and volatile organic and polyaromatic hydrocarbons.
- FIG. 1 is a cross-sectional view of an injector according to the invention.
- Fig. 2 is a schematic illustration of the supercritical water/fuel combustion system.
- the supercritical phase is a dense gas that is partially shifted to convert some of the reactants into H 2 and CO gases. These gases along with the hydrocarbons themselves exit a supercritical injector without passing through a liquid phase. As such, the concept of droplet atomization is completely eliminated from the reaction pathways.
- the temperature can be lowered a few degrees to the point where higher density sub- critical liquid is expelled. The jet then flash evaporates as it enters the cylinder.
- the interposed water molecules and water clusters provide catalytic surfaces for heterogeneous reactions.
- the H 2 gases are easily ignited and the ignition delay period is reduced. Accordingly, supercritical mixing raises the "effective cetane number" for the fuel mixture.
- the cetane value of diesel fuel is a parameter used to measure the flammability of the fuel. It is the exact opposite of the term octane in gasoline. In spark ignited combustion premature ignition is undesirable and hard to ignite fuels are desirable. The higher the octane rating the higher the compression ratio that can be employed and hence higher power output.
- Diesel engines on the other hand, rely on the auto ignition of the fuel via the interaction with heated intake air.
- the air is adiabatically heated during the compression stroke to over 700°C and fuel is injected near top dead center. Combustion ensues at a rate controlled by the fuel's cetane rating. Higher cetane fuels ignite sooner and provide more power along with improved specific fuel consumption.
- Supercritical mixing of diesel fuels and water alters the cetane rating implicitly. The water not only solvates the fuel molecules, but also reforms some fraction into CO and H 2 via the water shift reaction. In general, supercritical mixtures of hydrocarbons and water are subject to pyro lysis, hydrolysis, steam reforming, water gas shift reactions, methanation and hydrogenation to some extent.
- the cetane enhancement reduces ignition delay and extends the period of combustion.
- the temporal evolution of the pressure-volume characteristics can be quite different as the intimately mixed water may catalyze reaction along new coordinates. Reduced ignition delay means that fuel injection can be delayed and higher efficiencies anticipated.
- the supercritical combustion event is not expected to include reactions at the surface of liquid droplets.
- the complete elimination of surface tension under these conditions negates the possibility of droplet formation at air temperatures near the injector which generally exceed 800°C. Without droplet formation the entire nature of the combustion process is altered. As a result, local hot spots that promote NO formation are eliminated as there is no focused reaction at a droplet surface.
- the very high density of individual molecules in a supercritical fluid offers desirable reaction enhancing properties. These properties are directly related to the improved transport of reactants as the diffusivity of a dense gas is orders of magnitude greater than in a liquid state. The changes in reaction rates and reaction byproduct yield near the critical point of the water fuel mixtures can therefore be accomplished at higher rates and even along different reaction coordinates.
- Transport properties have been observed to vary by 3 - 4 orders of magnitude near T c ⁇ t . Above the critical temperature certain reaction byproducts are favored by increases in pressure whereas reactions that produce a liquid have reduced reaction rates. The reaction rates are not merely increased because the thermophysical properties are enhanced. Intrinsically different reaction coordinates begin to compete and shift the product concentration profiles. Normally, increasing the pressure of a gaseous system does not affect the chemical properties. Ideal gases remain ideal under pressure increases. Van der Waals gases remain weakly interacting. But critical fluids have a richness of detail that can only be accounted for by delocalized bonding interactions.
- Water has a density of about 1 gram/cm 3 below the critical temperature of 374°C with a critical pressure of about 3250psi.
- Diesel fuel has a wide range of molecular weight compounds and as such does not have a well defined critical temperature.
- the first experiment established a constant pressure of 2,000psi and the mixture was heated beyond the T c of water to 400°C. At 2,000psi and 400°C the pressure is too low and the temperature is too high to maintain water in the liquid state. And a dense gas forms on top of the still liquefied diesel fuel and no complete mixing is observed.
- One advantage is that the higher temperature will provide less ignition delay and will add enthalpy to the combustion process. Expanding the supercritical fuel mixture like a gas into the heated air in the cylinder provides better mixing and combustion at a molecular level and eliminates the time required for droplet evaporation. Use of exhaust heat to provide the required temperatures creates a thermodynamic regeneration which adds several percent to engine cycle efficiency in addition to accompanying improvements in emissions as a result of faster, more complete combustion.
- hydrocarbon fuels include, but are not limited to: gasoline, diesel fuel, heavy distillates, bunker C, kerosene, natural gas, crude oil, bitumen or any carbon containing material such as biomass. All of these hydrocarbon aggregations can be favored by mixing with water at or near supercritical conditions. As such, new refinery processes for fuel reformulation are permitted by judicious control of pressure, temperature and water content.
- an injector 10 circumvents the high temperature sealing problem by eliminating seals altogether.
- the injector 10 comprises a hermetically sealed enclosure 12 within which is disposed a magnetically activated needle valve assembly 14.
- a suitable material for the enclosure 12 is 17-4PH stainless steel which is closed by a magnetic iron cap 16 threaded on the top of the enclosure 12 sealed by copper gasket (not shown).
- the magnetically activated needle valve assembly 14 includes a magnetic iron armature 18 which is square shaped with rounded corners that fit within the internal diameter of the enclosure 12.
- the lower end of the assembly 14 includes a pintle valve 20 which normally closes the injector tip opening 22.
- the pintle 20 extends out of the small threaded end of the injector assembly 10 into the injector nozzle where it is held by spring 24.
- the spring 24 keeps the pintle 20 in contact with the opening 22 when the injector 10 is in its closed state.
- a two-layer solenoid of approximately 130 turns of number 14 magnet wire 26 is wound around an upper portion of the injector 10.
- the magnet wire 26 is insulated with 3M Nextel ceramic fiber.
- the upper portion wound with the magnetic wire 26 is approximately 5 inches long.
- the magnetic iron cap 16 is screwed onto the structure leaving a gap 28 of approximately 0.030 inch between the armature 18 and the cap assembly 16.
- the injector assembly 10 is actuated by a pulse width modulated 50 ampere pulse timed to, for example, a crankshaft of an engine.
- Fig. 2 is a schematic illustration of an embodiment of the invention utilizing the injector 10 of Fig. 1.
- a supply of fuel 30 and a supply of water 32 are connected to a pressure-limited dual-piston metering pump 34 which delivers water and fuel to an inlet 35 of the injector 10.
- the pump 34 provides the water and fuel at high pressure, approximately 4,000psi.
- the injector 10 is heated to approximately 400° by a heating jacket 36 which may be electrically powered or, more preferably, heated by a heat pipe (not shown) in contact with a heated exhaust manifold of an engine.
- the tip of the injector 10 is disposed to inject the homogeneous fuel/water mixture into the combustion chamber 38 of an engine 40.
- a power supply 42 is provided to energize the coil 26 and is timed with respect to the crankshaft 44 of the engine 40 to control fuel delivery .
- a temperature controller 46 maintains the appropriate temperature of the injector 10 so that the fluid therein is maintained at near supercritical conditions.
- Supercritical reaction chemistry is particularly valuable in fractionation columns because the solubility of species is a strong function of temperature and pressure.
- supercritical fluids shows solubilities that are quite unlike subcritical conditions. For example, salts that are highly soluble in hot water become insoluble above the critical temperature and precipitate out. Conversely, insoluble materials like hydrocarbons now dissolve readily above some critical temperature and pressure.
- the fuel injection system of the invention could be used in the combustor of a gas turbine or jet engine as used in aircraft, marine, automotive or stationary power applications.
- heat from the exhaust system is used to provide heat for the injector there results a heat regeneration cycle that extracts useful energy from the exhaust system which adds additional enthalpy to the combustion cycle near the peak of the compression cycle.
- the technology can also be used for processing heavy distillate fuels such that different molecular weights are selectively extracted according to pressure and temperature gradients within the supercritical reaction vessel.
- the technology can also be used for combusting fuels with higher molecular weight than kerosene and diesel fuel by the super solvating capability of the supercritical water.
- natural gas may be admitted into the supercritical and reformed mixture such that the mixture becomes hypergolic and autoignites in a compression engine without the need for pilot injection of a second fuel.
- the fuel injection system utilizes a flexible membrane forming a bellows-like structure for sealing the high pressure, high temperature mixture.
- a cam controls the motion of a valve acting through the flexible membrane.
Landscapes
- Fuel-Injection Apparatus (AREA)
- Output Control And Ontrol Of Special Type Engine (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US99289397A | 1997-12-18 | 1997-12-18 | |
US992893 | 1997-12-18 | ||
PCT/US1998/027012 WO1999031204A1 (en) | 1997-12-18 | 1998-12-18 | Supercritical water fuel composition and combustion system |
Publications (1)
Publication Number | Publication Date |
---|---|
EP1064344A1 true EP1064344A1 (en) | 2001-01-03 |
Family
ID=25538867
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP98967072A Withdrawn EP1064344A1 (en) | 1997-12-18 | 1998-12-18 | Supercritical water fuel composition and combustion system |
Country Status (1)
Country | Link |
---|---|
EP (1) | EP1064344A1 (en) |
-
1998
- 1998-12-18 EP EP98967072A patent/EP1064344A1/en not_active Withdrawn
Non-Patent Citations (1)
Title |
---|
See references of WO9931204A1 * |
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Legal Events
Date | Code | Title | Description |
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PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
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17P | Request for examination filed |
Effective date: 20000704 |
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AK | Designated contracting states |
Kind code of ref document: A1 Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE |
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18D | Application deemed to be withdrawn |
Effective date: 20030701 |
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RAP1 | Party data changed (applicant data changed or rights of an application transferred) |
Owner name: SUPERCRITICAL COMBUSTION CORPORATION |
|
D18D | Application deemed to be withdrawn (deleted) | ||
19U | Interruption of proceedings before grant |
Effective date: 20021209 |
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19W | Proceedings resumed before grant after interruption of proceedings |
Effective date: 20060201 |
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RAP1 | Party data changed (applicant data changed or rights of an application transferred) |
Owner name: NANOCLUSTER TECHNOLOGIES LLC |
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17Q | First examination report despatched |
Effective date: 20061030 |
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STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN |
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18D | Application deemed to be withdrawn |
Effective date: 20070510 |