Method for Generating Superheated Steam

Abstract

A method which develops a supercritical combustion chamber environment and combines fumigation and water conversion to superheated steam to effect greater fuel efficiency and reduce exhaust gas pollutants from a compression ignition engine. The invention utilizes the fumigant method by combining two gases (DME and heptane) which autoignite prior to the injection of the liquid water. This pre-combustion of the fumigant gases combined with the engine's compression of the combustion chamber gases is managed to attain a supercritical combustion chamber environment into which the liquid water is injected. This targeted supercritical combustion chamber environment causes the water to become a superheated steam, resulting in significantly greater efficiency and negligible exhaust gas pollutants resulting from the steam engine.

Claims

1. A method for creating superheated steam comprising: providing a compression ignition engine having a combustion chamber and a piston slidably moveable within a portion of said combustion chamber; providing a fumigant fuel charge to the combustion chamber to autoignite and create a supercritical environment in the combustion chamber prior to the injection of a water; injecting the principle working fluid, water, into the combustion chamber, wherein the water is converted to superheated steam after injection into the supercritical environment in the combustion chamber; and said superheated steam expands to force said piston outward.

2. The method for superheated steam of claim 1, wherein the fumigant fuel charge comprises a mixture of dimethyl ether and heptane.

3. The method for superheated steam of claim 1 wherein the fumigant fuel charge comprises 1-20% dimethyl ether and 80-99% heptane.

4. The method for superheated steam of claim 1 wherein the step of providing a fumigant fuel charge comprises injecting a fumigant fuel into an air intake port on the engine.

5. The method for superheated steam of claim 4 wherein the fumigant fuel charge is injected as a liquid.

6. The method for superheated steam of claim 4 wherein the fumigant fuel charge is injected as a gas.

7. The method for superheated steam of claim 1 wherein the liquid water is injected into the combustion chamber after top dead center (“TDC”).

8. The method for superheated steam of claim 1 wherein the liquid water is injected into the combustion chamber at 5° to 10° ATDC.

9. The method for superheated steam of claim 1 wherein the supercritical environment has a constant volume space pressure of at least 800 psi prior to the injection of the water.

10. The method for superheated steam of claim 1 wherein the supercritical environment has a temperature of 1,200° F. to 1,400° F.

11. A method for superheated steam creation in a compression ignition engine, the method comprising: combining two gases which autoignite prior to the injection of water, wherein the two gases are dimethyl ether and heptane; managing the pre-combustion of the fumigant gases combined with the engine's compression of the combustion chamber gases to attain a supercritical combustion chamber environment into which the water is injected and converted to steam.

12. A method for supercritical combustion comprising: providing a compression ignition engine having a combustion chamber; providing a fumigant fuel charge to the combustion chamber conditioned to autoignite to create a supercritical environment in the combustion chamber prior to the injection of a fuel, wherein said fuel is not the fumigant fuel; and injecting water into the combustion chamber after the chamber has been conditioned to a supercritical environment, wherein the water is raised from a liquid to a superheated steam.

13. The method for supercritical combustion of claim 12, wherein the fumigant fuel charge comprises a mixture of dimethyl ether and heptane and wherein the fumigant fuel charge comprises 1-20% dimethyl ether and 80-99% heptane.

14. The method for supercritical combustion of claim 12, wherein the step of providing a fumigant fuel charge comprises injecting a non-diesel fumigant fuel into an air intake port on the engine.

15. The method for supercritical combustion of claim 12, wherein the supercritical environment has a constant volume space of at least 800 psi prior to the injection of the fuel and wherein the supercritical environment has a temperature of 1,200 F to 1,400 F.

Description

BRIEF DESCRIPTION OF THF DRAWINGS

[0035] The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:

[0036] FIG. 1 is a cross sectional view of a two-stroke engine with the piston in the neutral exhaust/intake position;

[0037] FIG. 2 is a cross sectional view of the engine at the beginning of the compression stroke; and

[0038] FIG. 3 is a cross sectional view of the engine at the beginning of the power stroke.

DETAILED DESCRIPTION OF THF INVENTION

[0039] This invention applies to all compression ignition engines (CIE) which operate on diesel fuel No. 2, light fuel oil, biodiesel, water emulsified diesel fuels, water, steam or blends of diesel surrogates, light fuel oil emulsions, or blends of these fuels. This invention can be readily retrofitted onto existing CIE with only slight modification between installations on two-stroke and four-stroke CIE. This invention can also be readily implemented into new CIE design and construction. The apparatus and method will change dependent on the “family of CIE” to which it is applied. “Family of CIE” is intended to categorize as functional inclusionary units similar CIE. The broadest category is the division between two and four-stroke CIE. The method and apparatus will vary when adopted for use on the different families of CIE. Rotational speed, low, medium, high will be subfamilies, as will displacement volume of the combustion chamber.

[0040] The principle of this novel combustion method will remain the same. This principle is the use of a fumigant fuel blend to establish a supercritical fluid/gas environment within the combustion chamber of the CIE prior to the injection of the liquid diesel fuel. This supercritical fluid/gas environment has a target pressure of not less than 800 psi being expressed in the constant volume space (CVS) of the combustion chamber prior to the injection of the liquid diesel fuel. CVS is generally accepted to be the combustion space compressed by the piston commencing at 10° BTDC (before top dead center, the position of the piston prior to reaching TDC) and ending at 10° ATDC (after top dead center, the position of the piston after passing TDC). To achieve this pressure and corresponding temperature, 1,200° F. to 1,400° F., the components of the inventive method and apparatus will be adapted to perform for each family of CIE. The following detailed description is an embodiment of this invention as applied to a two-stroke uniflow medium speed CIE with a displacement of greater than 500 cubic inches per cylinder. The diesel fuel is injected by mechanical unit injectors.

[0041] This type of CIE utilizes either a Roots blower or a turbo charger to compress intake air into air chambers surrounding the lower portion of the cylinder assemblies, which comprise these engines power assemblies. These air boxes have access doors to which the fumigant fuel injector will be affixed and aimed at the nearest air intake port supplying the cylinder. This injector will inject liquid fumigant fuel supplied to it by a pressure vessel fuel tank which has an internal fuel pump to boost the tank pressure so that the fuel will remain liquid throughout its route to the injector. The pulse of the injector will be controlled by a device, which, at a minimum, constantly monitors the following engine parameters: the engine rpms to establish a timing sequence for the individual injection pulse, to be timed to pulse just as the intake ports are revealed by the piston and the air charge begins to enter the combustion chamber; and the continuous reading of the individual (e.g., every fourth cylinder) pressure developed during the entire engine cycle. This precise pressure information will be interpreted by a controller, which in turn will vary the fumigant fuel injector pulse duration to provide more or less fumigant fuel to the combustion chamber. The target is 800 psi being expressed in the CVS prior to the injection of the diesel fuel. At 800 psi and the relative temperature, 1,200° F. to 1,400° F., over 90% of the gases in the CVS are supercritical. H2O and CO2 will not be supercritical but N2, O2, OH, H2O2, and CO will all be supercritical.

[0042] The unit injector for the diesel fuel will be modified to inject the diesel fuel after TDC, e.g., 5° to 10° ATDC. The pulse duration of the unit injector will also be shortened. Because the atomized spray of the diesel fuel will encounter significantly higher combustion chamber pressure it will suffer greater shear force, greatly reducing the size of the diesel fuel droplets and ligaments. At the same time these droplets and ligaments will be innervated by the supercritical fluids/gases, which comprise the supercritical combustion chamber environment. As supercritical fluid/gases these substances become hyper-solvents.

[0043] The highly atomized diesel fuel droplets and ligaments are not only heated from the outside but also from the inside by both conduction and radiation. Supercritical substances release over 60% of their heat energy as radiant energy. At 800 psi the vaporization is delayed sufficiently to allow the combustion chamber supercritical environment to impart enough heat energy to the diesel fuel such that it transitions beyond its critical temperature point prior to initiation of significant combustion. The diesel fuel has already been pushed beyond its critical pressure point by the injectors and sustained beyond this critical pressure point by the pressure encountered in the combustion chamber. This transition beyond the critical temperature and pressure points has caused the diesel fuel to become a supercritical fluid, without surface tension and 100 times more dispersed into the supercritical combustion chamber environment. Combustion of the diesel fuel proceeds much more energetically than typical diesel fuel combustion and later in the rotation cycle of the CIE.

[0044] Typical diesel fuel combustion is timed for maximum heat release to occur in the CVS. The combustion event typically initiates just prior to the piston achieving 10° BTDC and continues to its high heat release thru 10° ATDC. Functionally from the combustion point of view, this sequence allows the diesel fuel to be reasonably combusted prior to the retained heat in the combustion chamber dropping below the temperature necessary to support combustion, about 60° ATDC. From a mechanical and heat management perspective this timing is wasteful and contributes to greater formation of NOx compounds. Mechanically, timing high heat release when the piston relationship to the crankshaft is essentially a vertical line is the time of lowest mechanical advantage and least possible transference of energy to aid in the rotation of the crankshaft. This high heat release is essentially stalled for almost a third of its active combustion sequence. The effect of this stall is to allow the heat to sink into the most readily available heat sinks, N2 and O2, 75% and 15% respectively of the combustion gases. This stalling of the combustion events mechanical transference and the companion sinking of heat into N2 creates CIE inefficiency and increased amounts of NOx in the exhaust gas.

[0045] In the inventive method, the combustion gases are supercritical which allows the timing of the diesel fuel combustion event to be delayed to a target of high heat release at 20° ATDC. At this crank angle the transference of energy is more mechanically favorable and allows the combustion chamber space to grow much more quickly than in typical CIE combustion, thus relieving the peak heat sinking and formation of significant NOx compounds.

[0046] This supercritical combustion chamber environment is created by combining the compression of the combustion chamber gases with a sequence of pre-diesel fuel injection combustion events. The fumigant fuel injected into the air intake is a blend, and preferably a custom blend, blended for each CIE family, of propane and dimethyl ether (DME). These fuels are miscible and combined in a single pressure vessel, blended specifically for the CIE family being served, but have been determined to range from 1-20% DME and 80-99% propane. In this example, the fumigant fuel is injected as a liquid. In the case of high rotational speed CIE family of engines the fumigant fuel would be injected as a gas for either two-stroke or four-stroke engines. Due to the low boiling point of the fumigant fuel components (−44° F. for propane and 11° F. for DME), these liquid fuels will vaporize in the early stages of the compression stroke and quickly homogenize with the air charge as the compression of the charge gases increases. At approximately 20° BTDC the DME will autoignite. This autoignition triggers the ignition of the propane. The fumigant fuel combustion is a two stage combustion so that the larger of the combustion events, the propane combustion, occurs just as the CVS is being entered into. This is done to lessen the backpressure on the piston. The DME combustion is principally a means to trigger the propane combustion.

[0047] The combustion chamber pressure may be continuously read by an in-cylinder pressure sensor, e.g. one for every four cylinders. The sensors output is interpreted by a controller, which increases or decreases the pulse duration of the fumigant fuel injector to best manage the fumigant fuel flow into the combustion chamber, to attain the target supercritical pressure prior to the diesel fuel injection.

[0048] Referring now to FIGS. 1 through 3, wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved method for supercritical diesel combustion.

[0049] The drawing figures illustrate a cross sectional view of a uniflow, two-stroke diesel engine. The operating principles apply as well to a four-stroke diesel engine, the difference being that the fumigant fuel injectors would be mounted on the four-stroke engines air intake manifold as close to each cylinders intake valves as possible. The fumigant fuel injector depicted is for application of the inventive system to existing diesel engines. Newly constructed engines could implement the system, optionally, by placing the fumigant fuel injector as a direct injection component, pulsing directly into the combustion chamber.

[0050] FIG. 1 depicts a two-stroke diesel engine 10 with the piston 12 at the point in which the piston is in the neutral exhaust/intake position. The exhaust valves 14 have opened just before the piston's descent which reveals the air intake ports 16 to allow the exhaust gas from the previous combustion to begin exiting thru the exhaust ports 18. As the piston continues to descend it reveals the air intake ports 16, which have been pressurized by the air compressor 20. All diesel engines operating on diesel fuel utilize some form of air compressor, such as a blower or turbocharger, to force air into the combustion chamber of the engine. Fresh intake air floods into the combustion chamber aiding in pushing the exhaust gases from the previous combustion out through the exhaust ports. Just as the fresh air begins to enter the combustion chamber the fumigant fuel injector 22, which is mounted and aimed directly at one of the air intake ports, pulses, releasing a specific volume of mixed fumigant fuel supplied by the fumigant fuel tank 24.

[0051] In low and moderate speed diesel engines (e.g., under 1200 rpm), the fumigant fuel will be injected as a liquid. High speed diesel engines will have the fumigant fuel injected as a gas to assure that complete vaporization and homogenization occurs prior to autoignition of the fumigant fuel. The fumigant fuel is a mixture of propane and dimethyl ether held in a common pressurized tank 24. Propane vaporizes at −44° F. and dimethyl ether vaporizes at −11° F., essentially both permanent gases at standard operating conditions.

[0052] FIG. 2 is a cross sectional view of the engine at the beginning of the compression stroke. The piston 12 continues to rise, closing off the air intake ports 16, the exhaust valves 14 have closed, and the compression stroke begins. As the piston slides towards the exhaust valves the combustion chamber gases are compressed and begin to rise in temperature. All diesel engines are designed so that the compression of these gases will increase in temperature well beyond the autoignition temperature of diesel fuel, prior to the piston entering the CVS. Typical diesel fuel compression ignition occurs as the diesel fuel is injected into the combustion chamber, initiating from approximately 16° BTDC. Operating with the inventive system the piston compresses the fumigant fuel air mixture 26 causing the fumigant fuel to vaporize and homogenize with the air charge. At approximately 20° BTDC the dimethyl ether will have achieved autoignition temperature and combust. This combustion will cause the propane to combust, which combined with the compression of the gases by the piston, will result in a supercritical combustion chamber environment.

[0053] FIG. 3 is a cross sectional view of the engine at the beginning of the power stroke, and the supercritical combustion chamber environment 32, with a CVS pressure of approximately 800 psi. At this pressure and corresponding temperature, 1,200 to 1,400° F., all the gases in the combustion chamber (except H2O and CO2) are supercritical fluids. Between 5° and 10° ATDC the diesel fuel from diesel fuel tank 28 is injected into this supercritical environment through diesel fuel injectors 30.

[0054] All diesel engines inject the diesel fuel at pressures 1,000's of psi above the diesel fuel critical pressure point. Because the CVS pressure is approximately 800 psi, roughly 2.5 times the critical pressure point of diesel fuel, the injected diesel fuel stays well above its critical pressure point. This injected diesel fuel is subjected to very high shear forces because of the increased pressure of the CVS, which increases atomization of the diesel fuel droplets and ligaments. The principle supercritical gases in the CVS are N2 and O2, which as supercritical fluids, act as hyper-solvents, innervating the diesel fuel droplets and ligaments thus imparting heat energy, over 60% as radiant energy, from within the diesel fuel droplet and ligament as well as from the exterior. This action by the supercritical hyper-solvents imparts heat energy into the diesel fuel such that the diesel fuel transitions into a supercritical state prior to combustion.

[0055] As a supercritical fluid diesel fuel does not have surface tension and is dispersed 100 times greater than as a liquid within the supercritical combustion chamber environment. The initiation of combustion of this supercritical diesel fuel is targeted to occur at 20° ATDC to take advantage of the maximum exertion of force at a time of greatest mechanical slider/crank leverage. Because the maximum heat release of the diesel fuel is now timed to take advantage of a much higher piston speed heat retention will be minimal and formation of NOx compounds will be significantly reduced.

In-Situ Steam Embodiment to Supercritical Diesel Combustion Patent

[0056] Another embodiment of the application of this invention is the use of the combination fumigant fuels of DME and heptane to create a supercritical chamber environment to heat water into a superheated steam, the principle gas expansion working fluid (PWF) acting upon the piston. Instead of having to inject a further combustible fuel such as glycerin or glycerin/water as shown in U.S. patent application Ser. No. 14/188,739 on Feb. 25, 2014, now U.S. Pat. No. 9,297,299 entitled “Method for Superheated Glycerin Combustion” which describes the combustion of a glycerin/water combination and is incorporated herein by reference, only water is added. Please note also that in the present application, the hexane of the '299 patent is preferably replaced by heptane, but use of either gas is anticipated by this invention.

[0057] The combination of these fuels (DME and heptane) injected along with the air charge of an internal combustion two stroke diesel engine will result in a two stage combustion process occurring prior to TDC. Using a 16 tol compression engine, the combustion sequence will begin between thirty and twenty degrees BTDC and will have fully combusted prior to the piston attaining TDC. As with the supercritical diesel combustion fumigant charge, the combustion space gases will in greater part become supercritical prior to the PWF being injected. The conditions of the cylinder after combustion and positioning of the piston with respect to top and bottom dead center (“TBC” and “BDC”) are provided above with respect to the diesel injection embodiment and are reincorporated here.

[0058] In the case of this embodiment, the main injected working fluid is liquid water instead of diesel or other combustible fuel. The water injection will occur between TDC and ten degrees ATDC. The supercritical gases already present in the combustion chamber will exchange their energy much quicker than the compressed air of the typical gases of a compression stroke air charge. The injected water instantly will become superheated steam. The expansion of water into steam provides the motive force to move the piston outward. The steam will then exit the cylinder during the exhaust stroke and may be recovered downstream, as is well known in the art. The use of steam obviates the need for other fuels such as diesel, though obviously the amount of power generated will be affected by the replacement fluid.

[0059] In a typical internal engine combustion event, the majority (e.g., over 60%) of the caloric value of the fuel is lost to the engine coolant system and to the heat of the exhaust gases. By staging a fumigant fuel pre-TDC combustion event and immediately following this combustion with water injection, the heat normally lost to the cooling and exhaust gases is retained (“absorbed”) in the phase change of the liquid water into steam. The efficiency of the engine is greatly enhanced and as a further benefit, the exhaust gases do not carry any significant amount of nitrous oxide compounds, particulate, or carbon compounds.

[0060] The object of this embodiment for fumigant charged ICE is to increase efficiency by capturing the heat of the combustive fumigant fuel before it can spread into the coolant system of the engine or be released to the atmosphere, and capturing the heat by converting it into steam and using the steam as a motive force.

[0061] The following description of this embodiment of supercritical fumigant combustion relies upon a two-stroke, uniflow, compression ignition engine design as depicted in FIGS. 1-3.

[0062] The fumigant fuel injector is a single hole direct injector placed at the highest intake port of the uniflow engine aimed at the interior of the cylinder. The preferred fumigant fuel is a mixture of dimethyl ether (“DME”) and heptane, though gases other than heptane could be used as described above. The DME is dissolved into the heptane in a ratio of between 20/1 to 40/1 depending on what field of use the engine is employed in and the engine size. This solution is retained in a pressure tank with sufficient pressure to keep the DME in the liquid state. The rail to the injectors is also kept at a pressure high enough to maintain the DME in the liquid state.

[0063] The fumigant fuel charge is approximately one third of the typical fuel charge required to support an ICE performance. The injection of the fumigant fuel is timed to occur just after bottom dead center (“BDC”) of the compression pistons travel and is swept into the now exposed cylinder cavity along with the intake air charge. Upon injection of the fumigant fuel the typically atomized droplets are further reduced as the DME immediately vaporizes and shatters the heptane/DME droplet, thus increasing the overall surface area of the remaining heptane droplet. Essentially creating a homogenous charge within the compressed air charge.

[0064] In a 16/1 compression engine, this homogenous charge will begin autoignition around 30 degrees BTDC and will have completed combustion at TDC. The resultant combustion chamber gases are now predominately supercritical. Because the fumigant fuel volume is never more than one third of the typical volume required by an ICE (“Internal Combustion Engine”), the combustion of the fumigant fuel charge is both more complete and does not attain the temperature at which NOx is formed. This thus lowers carbon emissions and NOx.

[0065] The water injector is placed as typical for an ICE. Performance is enhanced if the water is preheated by heat extracted from the ICE exhaust gases. Preheating in this fashion reduces the amount of fumigant fuel applied and facilitates condensation of the steam exhaust which, in part, reduces visual impact of the exhaust stream.

[0066] After TDC and before 10 degrees ATDC the water is injected into the supercritical gases present in the combustion chamber. The atomized water droplets are innervated by the supercritical gases and instantly absorb the heat of these gases and become superheated steam. This is a single step phase change reaction and is considerably faster than a combustion reaction. Also, the gas expansion ratio of water is greater than the expansion ratio of typical fuels. The result is significantly greater torque and efficiency of the ICE. As the steam is superheated, its deposition on the metal surfaces of the combustion chamber is minimal. The steam expansion is used to drive the piston 12 outwardly. During the exhaust phase, the steam is expelled from the cylinder is captured and reused as necessary in processes well known in the art. The piston drives a crankshaft or other or other device such a linear generator. The cylinder then begins the intake cycle and repeats as necessary.

[0067] The above disclosure is sufficient to enable one of ordinary skill in the art to practice the invention, and provides the best mode of practicing the invention presently contemplated by the inventor. While there is provided herein a full and complete disclosure of the preferred embodiments of this invention, it is not desired to limit the invention to the exact construction, dimensional relationships, and operation shown and described. Various modifications, alternative constructions, changes and equivalents will readily occur to those skilled in the art and may be employed, as suitable, without departing from the true spirit and scope of the invention. Such changes might involve alternative materials, components, structural arrangements, sizes, shapes, forms, functions, operational features or the like.

[0068] Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.