Patent Application
20120124897
The present disclosure generally relates to propellant formulations. Specifically, the present disclosure relates to the combination of hydrocarbon streams to manufacture rocket propellant having specific characteristics.
Currently, rocket propellant, in combination with liquid oxygen, is used as the propellant system in a large percentage of launch vehicles and rockets. However, supply is limited, resulting in little opportunity to optimize fuel formulations. Furthermore, limited supply results in little to no redundancy in supply in the event of supply shortages/failures.
Therefore, a need exists to develop alternative propellant formulations.
In certain embodiments of the present disclosure, a method of manufacturing a rocket propellant including combining at least two hydrocarbon fluids is disclosed.
A detailed description will now be provided. Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. The disclosure that follows includes specific embodiments, versions and examples, but the disclosure is not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the methods and compositions of matter disclosed when the information in this disclosure is combined with available information and technology.
Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition skilled persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing. Further, unless otherwise specified, all compounds described herein may be substituted or unsubstituted and the listing of compounds includes derivatives thereof.
Further, various ranges and/or numerical limitations may be expressly stated below. It should be recognized that any ranges include iterative ranges of like magnitude falling within the expressly stated ranges or limitations.
Embodiments of the present invention relate to formulated propellants. A large percentage of those vehicles are launch vehicles and rockets, while additional vehicles include hypersonic space planes, such as those powered by ramjets or scramjets, for example. Ramjets are generally jet engines that utilize a jet's forward motion to compress incoming air, which generally cannot produce thrust at zero airspeed and thus cannot move a jet aircraft from a standstill. A scramjet is a variant of the ramjet in which the combustion process takes place in supersonic airflow.
Rockets generate thrust by expelling mass behind them at high speed. Chemical rockets react propellant and oxidizer, such as liquid oxygen, in a combustion chamber creating a stream of high velocity gas to produce thrust. The current payloads of these vehicles are limited to a great extent by the density and energy content of the propellants.
Specific impulse of a rocket propellant (Isp) is a parameter that relates the thrust generated to the mass flow rate of propellant into the combustion chamber. The ratio is proportional to the square root of the chamber temperature and inversely proportional to the square root of the chamber content molecular weight. Thus, specific impulse increases with increasing chamber temperature (which results in higher chamber pressures) and decreasing molecular weight of combustion products (which achieve higher exhaust velocities than heavier products). Specific impulse is essentially a momentum term. Increasing the mass of fuel burned in a given amount of time or the velocity of the exhaust gases will generally have a beneficial effect on specific impulse. Higher specific impulses are desirable since greater thrusts are generated for a given weight of fuel combusted. The result is that a greater payload can be lifted into orbit or a higher orbit can be achieved than would otherwise be possible.
Many of the current users of propellant use a propellant that meets the “RP-1” specification (hereinafter referred to as an “RP-1 propellant”). Other users that are more sensitive to sulfur content require the use of a propellant that meets the RP-2 specification. Certain relevant chemical and physical property specifications for RP-1 and RP-2 propellants are shown in Table 1 below.
Traditionally, RP-1 propellants are highly refined kerosene similar to jet fuel. Kerosene is generally obtained from the fractional distillation of petroleum between 140° C. and 250° C., resulting in a mixture of molecules with carbon chains lengths between 10 and 25 carbon atoms. For example, RP-1 propellants may have an average molecular weight of about 175, a density of about 0.82 g/ml and a boiling point range of from 350° F. (176° C.) to 525° F. (273° C.). Theoretically, nearly any petroleum crude oil can produce some RP-1 propellants with enough processing; however, in practice, the fuel is typically sourced from a small number of oil fields with high-quality base stock due to the costs and difficulty involved in refining lesser-quality crudes.
Unlike traditional methods of manufacturing RP-1 propellants, the propellants of the present invention are formulated by blending one or more hydrocarbon fluids to form formulated propellants.
As used herein, the term “hydrocarbon fluids” is used in a generic sense to describe a wide range of materials used in an equally wide range of applications. The hydrocarbon fluids generally utilized for the formulated propellants described herein may be produced by a number of processes. For example, hydrocarbon fluids can be produced from severe hydrotreating, deep hydrotreatment or hydrocracking to remove sulfur and other heteroatoms or polymerization or oligomerization process, such processes being followed by distillation to separate them into narrow boiling ranges. In some cases there may be additional steps, such as chemical or physical separation in order to concentrate a stream into isoparaffins or paraffins. Further, isoparaffins derived from oligomerization may constitute hydrocarbon fluids.
Certain hydrocarbon fluids are described in U.S. Pat. No. 7,311,814 and U.S. Pat. No. 7,056,869, which are incorporated by reference herein. Unlike fuels, hydrocarbon fluids tend to have a narrow boiling point range, e.g., less than 500° F. (260° C.), or 300° F. (148° C.) or 100° F. (37° C.), for example. Such narrow cuts provide a more narrow flash point range and provide for tighter viscosity, improved viscosity stability and defined evaporation specifications, as shown by the distillation curve, for example.
In certain embodiments, the hydrocarbon fluids may be produced by hydrocracking a vacuum gas oil distillate followed by fractionating and/or hydrogenating the hydrocracked vacuum gas oil. Such fluids may have an ASTM D86 boiling point range of from 212° F. (100° C.) to 752° F. (400° C.), wherein the individual hydrocarbon fluids may have the narrower boiling ranges described herein. The fluids may further have a naphthenic content of at least 40 wt. %, or 60 wt. % or 70 wt. %, for example. The fluids may further have an aromatics content of less than 2 wt. %, or 1.5 wt. % or 1.0 wt. %, for example. The fluids may further have an aniline point below 212° F. (100° C.), or 205° F. (96° C.) or 200° F. (93° C.), for example.
In certain embodiments, the hydrocarbon fluids have low sulfur concentrations e.g., less than 30 ppm, or less than 15 ppm or less than 3 ppm, aromatics contents that are below 1.0 vol. %, or 0.5 vol. % or 0.01 vol. %, for example, relatively high net heats of combustion, and narrow distillation ranges. Further, depending on how the hydrocarbon fluid is processed and produced, the hydrocarbon fluid may be further characterized as predominantly paraffinic, isoparaffinic, or naphthenic (e.g., greater than 40 wt. %, or 50 wt. % or 60 wt. % or 80%). While such characterization may be helpful in blending to achieve very low densities and/or high net heats of combustion, such characterization is not a necessary condition for formulation of propellants.
Some illustrative, non-limiting chemical and physical property ranges characterizing various hydrocarbon fluids are shown in Table 2 below.
The hydrocarbon fluids can be derived from any suitable starting material that can result in materials that meet the final use requirements. It is to be noted that starting materials need not fall into final product boiling range, as in the gas oil case stated above. Thus, starting materials for production of hydrocarbon fluids can be gas oils or other high molecular weight material (that are further hydrocracked to lower molecular weight materials or deep hydrotreated to decrease sulfur content, materials that are normally classified as distillates, such as kerosene, straight run diesel, ultralow sulfur diesel, coker diesel (with sufficient hydroprocessing), or light cycle oil from FCC units, for example. Starting materials can be kerosene or gas oils from Gas to Liquid process or from biomass conversion processes. After sufficient hydroprocessing to remove oxygen, In certain embodiments, biodiesel and biojet are used as starting materials. Typically, biodiesel and biojet are hydroprocessed to remove oxygen. In certain embodiments, triglycerides that, after processing yield a carbon chain in the C12 to C18 range, are used as starting materials. Biodiesel and biojet may be plant or animal sourced. Additionally, the starting materials may be olefins to produce the hydrocarbon fluids, olefins being polymerized or oligomerized. In one or more embodiments, the starting materials may include propene, butene or combinations thereof, for example. Olefins may be produced from traditional sources such as a naphtha cracker. Alternatively, in certain embodiments of the present disclosure, olefins are produced from dehydration of low carbon number alcohols. Low carbon number alcohols may be produced through various biomass fermentation processes. In certain embodiments, hydrocarbon fluids can include gas oil, kerosene, straight run diesel, ultralow sulfur diesel, coker diesel, light cycle oil, hydrodewaxed gasoil or kerosene cuts, ethylene, propene, butene or combinations thereof.
In one or more embodiments, the hydrocarbon fluids are generally components selected from C9-C18 or narrower distillation cuts. Specific, non-limiting, examples of distillation cuts characterizing hydrocarbon fluids that may be blended to form the formulated propellant include SPIRDANE® (e.g., D-40 having a density of about 0.790 g/mL, a boiling range of 356° F.-419° F. (180-215° C.), flash point of 107.6° F. (42° C.) and D-60 having a density of about 0.770 g/mL, a boiling range of 311° F.-392° F. (155-200° C.), flash point of 145° F. (62° C.)), KETRUL® (e.g., D-70 having a density of about 0.817 g/mL, a boiling range of 381° F.-462° F. (193-238° C.), flash point of 160° F. (71° C.) and D-80 having a density of about 0.817 g/mL, a boiling range of 397° F.-465° F. (202-240° C.), flash point of 170.6° F. (77° C.)), HYDROSEAL® (e.g., G 232 H) and ISANE IP® fluids, commercially available from TOTAL FLUIDES, S.A., ISOPAR™ fluids, commercially available from ExxonMobil Chemical Corp. and IP2835, commercially available from Idemitsu Corp.
With the information and methods provided in this disclosure, it is possible to formulate a propellant with particular desired characteristics by blending hydrocarbon streams. In one or more embodiments, the formulated propellants include two or more hydrocarbon fluids. For example, in some embodiments, the formulated propellant includes two hydrocarbon fluids. In other embodiments, the formulated propellant includes three hydrocarbon fluids. In still other embodiments, the formulated propellant includes four hydrocarbon fluids. Individual hydrocarbon fluids are chosen for formulation into propellants depending on how each contributes to the final properties of a rocket fuel blend.
In one or more embodiments, the formulated propellant is formulated to exhibit a particular distillation curve or aspects of a particular distillation curve. For instance, in certain embodiments, the formulated propellant may be designed to have a front end within the fuel evaporated limits designated in Table 1 and an endpoint at or below the temperature of the endpoint specified in Table 1. In such an instance, a plurality of hydrocarbon fluids may be blended to create a formulated propellant that meets the RP-1 specifications for “fuel evaporated” and “end point.”
It is not necessary for the individual hydrocarbon fluids that are to be blended to each have particular fluid characteristics, such as end point or fuel evaporated, within the specification desired. That is, the formulated propellant may be formulated from a broad spectrum of hydrocarbon fluids that in and of themselves do not meet the desired specification. Further, known jet fuel formulations may be incorporated with the hydrocarbon fluid. By utilizing such combinations, a broader tailored property distribution is achievable. For example, a specific, non-limiting formulated propellant may be formed of a first hydrocarbon fluid having an end point higher than the desired specification while a second hydrocarbon fluid may have an end point below that of the desired specification to achieve a blend that has an end point that falls within the desired specification. Further, by selecting the individual hydrocarbon fluids, it may be possible to replicate a desired distillation curve within an acceptable margin.
While in certain circumstances a single hydrocarbon fluid may be used as a propellant, such as one that falls within or overlaps the distillation range for a particular propellant specification, such as RP-1, the combination of two or more fluids results in greater flexibility in how closely it is possible to match the entirety of the desired distillation curve. For instance, when matching two points within the specification for RP-1 propellant distillation curves, for example the 10% and final point, it may not be necessary to match the entire RP-1 propellant curve to be within the specification. However, by combining two or more hydrocarbon fluids, it is possible to achieve a formulated propellant that more closely matches the desired distillation curve, thereby improving performance or standardizing performance, for instance.
In addition to blending hydrocarbon fluids to reach certain points on a distillation curve, such as the fuel evaporated 10% and endpoint, hydrocarbon fluids may be blended to achieve numerous other characteristics. For instance, hydrocarbon fluids may be blended to achieve formulated propellants with certain cold flow properties such as pour point, cloud point, freeze point and viscosity. In other embodiments, hydrocarbon fluids may be blended to achieve certain propellant performance characteristics, such as density, hydrogen content, and net heat of combustion.
As an example, in some embodiments, hydrocarbon fluids that have a flash point below the RP-1 propellant specification of 140° F. (60° C.) may be used in the formulation, but only in amounts that do not reduce the flash point of the final blend below the specification. Similarly, fluids with freeze points above the −60° F. (−51° C.) maximum specification, such as those with a minor amount of aromatics, may be included in the blend as long as the final freeze point is below the RP-1 propellant specification value.
The use of hydrocarbon fluids from which aromatics have been reduced/removed yields another benefit to the propellant. In certain embodiments, the reduced amount of aromatics in the hydrocarbon fluid components leads to a higher net heat of combustion for the hydrocarbon fluids components used as blend stock. In certain embodiments, the combination of these high net heat of combustion hydrocarbon fluids results in a product that exceeds the 18,500 BTU/pound minimum specification of RP-1 propellant. In certain embodiments of the present disclosure, the net heat of combustion is from 18,500 BTU/pound to 19,000 BTU per pound as measured by ASTM D-240. In other embodiments of the present disclosure, the net heat of combustion is between 18,700 BTU/pound to 18,900 BTU/pound as measured by ASTM D-240. Further, the use of hydrocarbon fluids from which aromatics have been removed or reduced may also increase hydrocarbon content of the formulated propellant.
In addition, isoparaffinic blend stocks may help to raise the net heat of combustion when included in the blend, as such blend stocks' net heat of combustion is greater than aromatics or naphthenics that are characterized by the same carbon number. Normal paraffin blend stock may also raise the net heat of combustion.
Different blend stocks may have different rates of combustion. Typically, designers of rocket engines prefer a particular range or rate of combustion in order to make sure the flame front propagates through the rocket engine at a desired rate. A rate of combustion that is too fast may result in combustion completion before the desired point in the engine. A rate of combustion that is too slow may result in the opposite problem. Typically, normal parrafins have a very high rate of combustion. Isoparrafins typically have a lesser rate of combustion. In certain embodiments of the present disclosure, the isoparrafin/paraffin ratio of the blend stocks are controlled to achieve an optimized rate of combustion for the formulated propellant.
Density is an important parameter of the propellant as it determines the weight of the fuel that must be lifted by the vehicle. Within the framework of the desired distillation curve, hydrocarbon fluids may be chosen to alter the density of the final blend. For example, naphthenic based fluids will tend to raise the final density while isoparaffinic fluids tend to reduce the density of the final product. Materials that contain a significant amount of naphthenes and are at the high end of the distillation curve relative to a propellant specification such as RP-1, such as HYDROSEALS®, can be used to increase the density of the blended product. In certain embodiments of the present disclosure, the density at 15° C. is between 0.77 and 0.82, between 0.799-0.815, between 0.81 to 0.8135, and between 0.77 to 0.80, as measured by D-1298.
Accordingly, one or more embodiments utilize isoparaffin hydrocarbon fluids as at least one of the two or more hydrocarbon fluids. In one or more embodiments, the propellant may include a first hydrocarbon fluid having a density greater than 0.8 g/ml and a second hydrocarbon fluid having a density less than 0.8 g/ml, for example. The formulated propellants may have a weight that is about 5%, or 7% or 9% less than the weight of the RP-1 propellant, for example.
Hydrogen content of the propellant has a significant effect on the performance of the propellant. Generally, the higher the hydrogen content, the higher the Isp of the propellant. In certain embodiments, in order to keep the exhaust molecular weight low, the rocket engine is run slightly fuel rich to produce CO rather than CO2 as a combustion product. As the hydrogen content is increased, the amount of oxidizer needed (the mixture ratio) to combust the propellant also may increases because more atoms are present for a given carbon number compound. Specifically, an increase in the fuel hydrogen to carbon ratio results in a stoichiometric oxygen to fuel ratio increase. Thus, more moles of gas are expelled from the exhaust nozzle as combustion products. When those additional moles of gas are water, the average molecular weight of the exhaust gas goes down. Additionally, a significant amount of molecular fragments of OH and hydrogen atoms are formed and ejected from the combustion chamber. The proportion of these also may increase with an increase in hydrogen to carbon ratio and further reduce the average molecular weight of the exhaust gas.
In certain embodiments of the present disclosure, the hydrogen content of the formulated propellant is controlled by increasing the ratio of hydrogen of carbon atoms of the molecules of the hydrocarbon fluid blend stocks. For instance, reducing rings and branching and increasing the degree of hydrogen saturation of hydrocarbon molecules increases the hydrogen:carbon atom ratio, thereby increasing hydrogen content of the propellant. Removing or reducing aromatics in the hydrocarbon fluid blend stocks may result in a significant increase in hydrogen content. Hydrogen content in certain embodiments of rocket propellant of the present disclosure are from 14.25-15 wt %, from 14-14.8 wt %, less than 15.3 wt %, and between 14.8 and 15 wt % as measured by ASTM D-3343
Typically, the hydrocarbon fluids used in the blended formulated propellant have very low sulfur concentration. Sulfur adversely affects propellant performance in a number of ways, including reducing the net heat of combustion and increasing fouling. Therefore in some embodiments, the formulated propellants include significantly reduced sulfur contents compared to conventional RP-1 propellants. For example, the formulated propellants may include less than 30 ppm or less than 5 ppm sulfur. In other embodiments, the formulated propellants contain less than 3 ppm sulfur or less than 1 ppm sulfur.
Due to the significant absence of olefins and aromatics from the formulated propellant, the formulated propellants exhibit improved thermal stability over a traditionally manufactured RP-1 propellant. Engines utilized in the vehicles described herein may include cooling coils around an exhaust nozzle through which fuel from tanks flows prior to injection into a combustion chamber. The cooling coils periodically foul, in large part due to aromatics and/or olefins present in the propellant. Accordingly, the formulated propellants provide a fuel that may allow reuse of booster stage rocket motors due to significantly reduced, if not eliminated, cooling coil fouling, for example.
Traditionally manufactured RP-1 propellant may be used in both the booster stage and in upper stages. However, it is more common for upper stages to include or entirely use higher energy fuels because of density and performance issues with RP-1. As one of ordinary skill in the art can appreciate with the benefit of this disclosure, by manipulating the performance parameters of the formulated propellant, formulated propellants consistent with this disclosure may be used in upper stages, either alone, or in combination with higher energy fuels. In certain embodiments of the present disclosure, the formulated propellant may be combined with powdered metal capable of forming a metal oxide in order to achieve a higher level of specific impulse. One example of such a metal is aluminum.
The formulated propellants of the present disclosure overcome problems of certain traditional RP-1 propellants' availability/performance by blending existing hydrocarbon fluids to produce a propellant at least equal in properties and cost, if not superior to, traditionally manufactured RP-1 propellants. Further, the formulated propellants of the present disclosure can be tailored to provide properties such as density, hydrogen content, and heat of combustion while exhibiting the ability to maintain a higher level of specific impulse (Isp) than that available with conventionally manufactured RP-1.
It is further contemplated that the formulated propellant may contain various additives, such as dyes, antioxidants, metal deactivators, and combinations thereof, for example.
A sample of traditionally manufactured RP-1 propellant and samples of various formulated propellants were analyzed by D-86, density, aniline point, cloud point, sulfur content, and aromatics content by FIA. The distillation curve and density were used to calculate hydrogen content by ASTM D-3343. The distillation curve, density, aniline point, sulfur content, and aromatics content were used to calculate the net heat of combustion by ASTM D-4529. As a basis for comparison, a sample of traditionally manufactured RP-1 propellant was obtained and analyzed, with results illustrated in the data below. The density was measured at 15° C., as required by ASTM D-4529, which is an estimation of the net heat of combustion. Subsequent density measurements made on formulated propellants were done on the same basis. The latter was used to calculate the net heat of combustion.
For the traditionally manufactured RP-1 propellant, sulfur content was well below the 30 ppm maximum. Cloud point was measured instead of freeze point (the latter being at a lower temperature than the former). The hydrogen content was calculated using the empirical formulas in ASTM D-3343, which utilizes the density, distillation curve, and aromatics content. The value was 14.27%, surpassing the specification of 13.8% (wt). Further, there was a small amount of aromatics and olefins present, 1.22 and 1.10% (vol), respectively, which slightly reduce the hydrogen content. The theoretical maximum hydrogen content for a C12-C18 kerosene cut is between 14.9 and 15.3%. As a highly hydrotreated kerosene, the traditionally manufactured RP-1 propellant would also be characterized by the presence of naphthenic rings. Its hydrogen content of 14.3% was consistent with a single naphthenic ring per molecule. The traditionally manufactured RP-1 propellant distillation curve is shown in
The materials analyzed for use in the formulated propellants were SPIRDANE® D-40, SPIRDANE® D-60, KETRUL® D-70, KETRUL® D-80, HYDROSEAL® G 232 H, ISANE IP® 175, and ISANE IP® 185. The distillation curves for these components are shown in
The density measurements for all components excluding the ISANE IP® materials were close to that of the traditionally manufactured RP-1 propellant. ISANE IP® materials were characterized by a lower density than that of the traditionally manufactured RP-1 propellant. The net heats of combustion and hydrogen content for those components, including ISANE IP® materials, were comparable to the traditionally manufactured RP-1 propellant.
Once component data was compiled, the formulated propellants were made. A number of prototype blends were made to gauge how the components affected each other in combination. Three prototypes were made and designated proto-6, proto-7, and proto-8. Proto-6 was designed to match the RP-1 specification. Proto-7 and proto-8 were designed to be lower boiling and higher boiling than the RP-1 specification, on average, respectively. The latter two were made to determine what range of density and other properties would be achievable with the current blend components, such as SPIRDANE®, KETRUL®, and HYDROSEAL® based materials if the limits of the distillation curve were pushed. Blend formulations for the prototypes are shown in Table 3.
The distillation curve data for proto-6, proto-7, proto-8 and traditionally manufactured RP-1 propellant is shown in
A high concentration of the light D-60 component reflected in the position of the proto-7 distillation curve below all others tested. Similarly, the high concentration of the heavy component G232H raised the proto-8 distillation curve above all the others.
Cloud point data for all formulations was below the freeze specification of −60° F. (−51° C.) indicating that all have an acceptable freeze point. The sulfur content of the traditionally manufactured RP-1 propellant was measured at 1 ppm by wavelength dispersive x-ray fluorescence, as noted earlier. Prototype formulations were at the limit of detection for that method with measurements at 0.5-0.6 ppm. These values are very close to the 0.1 ppm max limit for an RP-2 formulation. The density measurements were very close to that of the traditionally manufactured RP-1 propellant, albeit slightly higher, but still within the RP-1 specification. This was consistent with the density of the blend stocks that were slightly above that of the traditionally manufactured RP-1 propellant. The density measurements are compared in
ISANE IP® 175 and 185 are characterized by densities significantly lower than the traditionally manufactured RP-1 propellant, but have flash points that are at or above that of the RP-1 specification. The density of each of these was below 0.77 g/ml, a significant reduction relative to other blend components and the traditionally manufactured RP-1 propellant. Additionally, the hydrogen content was measured between 15.1 and 15.2. This is in agreement with the theoretical value for a fully saturated sample with no naphthenic rings in the C12 to C18 range and as reflected by typical values reported on the certificate of analysis for these materials.
The distillation curve data for traditionally manufactured RP-1 propellant is shown in
The distillation curves corresponding to the new formulations are shown in
The immediate effect of the presence of replacing the lower boiling components with isoparaffins can be seen on the density measurement in
The hydrogen content for the prototypes is shown in
The net heat of combustion for the prototypes is shown in
In addition to the above proto-formulations, proto-20 was formulated. Proto-20, like proto-6 and proto-9 was designed to match within reasonable limits the distillation curve associated with traditionally produced RP-1 propellant.
Six thousand gallons of proto-6 were prepared in a commercial scale facility. As shown in
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof and the scope thereof is determined by the claims that follow.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12949980 | Nov 2010 | US |
| Child | 13295268 | US |
