Patent Publication Number: US-2023151724-A1

Title: Bi-fuel reciprocating engine to power direct drive turbine fracturing pumps onboard auxiliary systems and related methods

Description:
PRIORITY CLAIM 
     This is a continuation of U.S. Non-Provisional application Ser. No. 17/663,294, filed May 13, 2022, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” which is a continuation of U.S. Non-Provisional application Ser. No. 17/653,893, filed Mar. 8, 2022, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,365,616, issued Jun. 21, 2022, which is a continuation of U.S. Non-Provisional application Ser. No. 17/481,794, filed Sep. 22, 2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,313,213, issued Apr. 26, 2022, which is a divisional of U.S. Non-Provisional application Ser. No. 17/301,241, filed Mar. 30, 2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,208,880, issued Dec. 28, 2021, which claims priority to and the benefit of, under 35 U.S.C. § 119(e), U.S. Provisional Application No. 62/705,188, filed Jun. 15, 2020, titled “BI-FUEL RECIPROCATING ENGINE TO POWER ONBOARD FRACTURING PUMP AUXILIARY SYSTEMS AND RELATED METHODS,” and U.S. Provisional Application No. 62/704,774, filed May 28, 2020, titled “SYSTEMS AND METHODS FOR SUPPLYING PRIMARY FUEL AND SECONDARY FUEL TO AN INTERNAL COMBUSTION ENGINE OF A FRACTURING UNIT,” the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to systems and methods for supplying fuel to an internal combustion engine of a fracturing unit and, more particularly, to systems and methods for supplying a primary fuel and a secondary fuel for operation of an internal combustion engine associated with a hydraulic fracturing unit. 
     BACKGROUND 
     Fracturing is an oilfield operation that stimulates production of hydrocarbons, such that the hydrocarbons may more easily or readily flow from a subsurface formation to a well. For example, a fracturing system may be configured to fracture a formation by pumping a fracturing fluid into a well at high pressure and high flow rates. Some fracturing fluids may take the form of a slurry including water, proppants, and/or other additives, such as thickening agents and/or gels. The slurry may be forced via one or more pumps into the formation at rates faster than can be accepted by the existing pores, fractures, faults, or other spaces within the formation. As a result, pressure builds rapidly to the point where the formation may fail and may begin to fracture. By continuing to pump the fracturing fluid into the formation, existing fractures in the formation are caused to expand and extend in directions farther away from a well bore, thereby creating flow paths to the well bore. The proppants may serve to prevent the expanded fractures from closing when pumping of the fracturing fluid is ceased or may reduce the extent to which the expanded fractures contract when pumping of the fracturing fluid is ceased. Once the formation is fractured, large quantities of the injected fracturing fluid are allowed to flow out of the well, and the production stream of hydrocarbons may be obtained from the formation. 
     Prime movers may be used to supply power to a plurality of fracturing pumps for pumping the fracturing fluid into the formation. For example, a plurality of gas turbine engines may each be mechanically connected to a corresponding fracturing pump and may be operated to drive the corresponding fracturing pump. A fracturing unit may include a gas turbine engine or other type of prime mover and a corresponding fracturing pump, as well as auxiliary components for operating and controlling the fracturing unit, including electrical, pneumatic, and/or hydraulic components. The gas turbine engine, fracturing pump, and auxiliary components may be connected to a common platform or trailer for transportation and set-up as a fracturing unit at the site of a fracturing operation, which may include up to a dozen or more of such fracturing units operating together to perform the fracturing operation. In order to supply electrical, pneumatic, and/or hydraulic power for operation of the auxiliary components, an additional prime mover may be used. For example, another internal combustion engine may be used and may have a relatively reduced rated output as compared to the prime mover used for driving the fracturing pump. However, the additional prime mover may have different fuel requirements, which may be costly and/or may be prone to producing significant additional undesirable emissions. Thus, the additional internal combustion engine may increase costs and result in higher emissions than desired. 
     Accordingly, Applicant has recognized a need for systems and methods that provide greater efficiency and/or reduced emissions when performing a fracturing operation. The present disclosure may address one or more of the above-referenced drawbacks, as well as other possible drawbacks. 
     SUMMARY 
     The present disclosure generally is directed to systems and methods for supplying fuel to an internal combustion engine associated with a hydraulic fracturing system. For example, in some embodiments, a system to supply primary fuel and secondary fuel to operate an internal combustion engine may include a first manifold positioned to provide fluid flow from a primary fuel source of primary fuel to an internal combustion engine. The system also may include a primary valve associated with the first manifold and positioned to provide fluid flow between the primary fuel source and the internal combustion engine. The system further may include a second manifold positioned to provide fluid flow from a secondary fuel supply of secondary fuel to the internal combustion engine. The system still also may include one or more of a fuel pump or a secondary valve associated with the second manifold and positioned to provide fluid flow between the secondary fuel source and the internal combustion engine. The system still further may include a controller in communication with one or more of the primary valve, the fuel pump, or the secondary valve and may be configured to receive one or more signals indicative of one or more of a hydraulic power load on the internal combustion engine or an electric power load on the internal combustion engine. The controller also may be configured to determine, based at least in part on the one or more signals, a total power load on the internal combustion engine, and determine, based at least in part on the total power load, a first amount of primary fuel to supply to the internal combustion engine and a second amount of secondary fuel to supply to the internal combustion engine. The controller further may be configured to cause, based at least in part on the first amount and the second amount, one or more of the primary valve, the fuel pump, or the secondary valve to operate to supply the first amount of primary fuel and the second amount of secondary fuel to the internal combustion engine. 
     According to some embodiments, a fracturing unit may include a chassis and a fracturing pump connected to the chassis and positioned to pump a fracturing fluid. The fracturing unit also may include a gas turbine engine connected to the chassis and positioned to convert fuel into a power output for operating the fracturing pump. The fracturing unit further may include a reciprocating-piston engine connected to the chassis and positioned to supply power to operate one or more of hydraulic auxiliary components or electrical auxiliary components associated with the fracturing unit. The fracturing unit also may include a first manifold positioned to provide fluid flow from a primary fuel source of primary fuel to the gas turbine engine and the reciprocating-piston engine. The fracturing unit still may include a second manifold positioned to provide fluid flow from a secondary fuel supply of secondary fuel to the reciprocating-piston engine. The fracturing unit additionally may include a controller configured to receive one or more signals indicative of operation of one or more of the hydraulic auxiliary components or the electrical auxiliary components, and determine, based at least in part on the one or more signals, a first amount of primary fuel to supply to the reciprocating-piston engine and a second amount of secondary fuel to supply to the reciprocating-piston engine. The controller also may be configured to cause, based at least in part on the first amount and the second amount, supply of the first amount of primary fuel and the second amount of secondary fuel to the reciprocating-piston engine. 
     According to some embodiments, a method for supplying primary fuel and secondary fuel to a reciprocating-piston engine may include determining a total power load on the reciprocating-piston engine due to operation of one or more of hydraulic auxiliary components supplied with power by the reciprocating-piston engine or electrical auxiliary components supplied with power by the reciprocating-piston engine. The method further may include determining, based at least in part on the total power load, a first amount of primary fuel to supply to the reciprocating-piston engine and a second amount of secondary fuel to supply to the reciprocating-piston engine. The method further may include causing, based at least in part on the first amount and the second amount, one or more of: a primary valve to operate to supply the first amount of primary fuel to the reciprocating-piston engine, or one or more of a fuel pump or a secondary valve to operate to supply the second amount of secondary fuel to the reciprocating-piston engine. 
     Still other aspects and advantages of these exemplary embodiments and other embodiments, are discussed in detail herein. Moreover, it is to be understood that both the foregoing information and the following detailed description provide merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Accordingly, these and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and may exist in various combinations and permutations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the embodiments of the present disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure, and together with the detailed description, serve to explain principles of the embodiments discussed herein. No attempt is made to show structural details of this disclosure in more detail than can be necessary for a fundamental understanding of the embodiments discussed herein and the various ways in which they can be practiced. According to common practice, the various features of the drawings discussed below are not necessarily drawn to scale. Dimensions of various features and elements in the drawings can be expanded or reduced to more clearly illustrate embodiments of the disclosure. 
         FIG.  1    schematically illustrates an example fracturing system including a plurality of hydraulic fracturing units, including a detailed schematic view of an example system for supplying primary fuel and secondary fuel to an example internal combustion engine according to an embodiment of the disclosure. 
         FIG.  2    is a schematic view of an example system for supplying primary fuel and secondary fuel to an example internal combustion engine to provide power for example hydraulic auxiliary components and example electrical auxiliary components according to an embodiment of the disclosure. 
         FIG.  3    is a graph showing an example relationship of percentage of primary fuel supplied to operate an internal combustion engine as a function of a percent of maximum power output by the internal combustion engine according to an embodiment of the disclosure. 
         FIG.  4    is a graph showing an example relationship of efficiency of an internal combustion engine as a function of a percentage of maximum power output by the internal combustion engine according to an embodiment of the disclosure. 
         FIG.  5    is a schematic view of another example fracturing system including a plurality of hydraulic fracturing units receiving primary fuel from an example primary fuel source according to an embodiment of the disclosure. 
         FIG.  6    is a block diagram of an example method for supplying primary fuel and secondary fuel to a reciprocating-piston engine according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The drawings include like numerals to indicate like parts throughout the several views, the following description is provided as an enabling teaching of exemplary embodiments, and those skilled in the relevant art will recognize that many changes may be made to the embodiments described. It also will be apparent that some of the desired benefits of the embodiments described can be obtained by selecting some of the features of the embodiments without utilizing other features. Accordingly, those skilled in the art will recognize that many modifications and adaptations to the embodiments described are possible and may even be desirable in certain circumstances. Thus, the following description is provided as illustrative of the principles of the embodiments and not in limitation thereof. 
     The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. As used herein, the term “plurality” refers to two or more items or components. The terms “comprising,” “including,” “carrying,” “having,” “containing,” and “involving,” whether in the written description or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to,” unless otherwise stated. Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. The transitional phrases “consisting of” and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to any claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish claim elements. 
       FIG.  1    schematically illustrates an example fuel delivery system  10  for supplying fuel to a plurality of hydraulic fracturing units  12 , including a detailed schematic view of an example fuel line connection assembly  14  according to embodiments of the disclosure. The fuel delivery system  10  may be part of a hydraulic fracturing system  16  that includes a plurality (or fleet) of hydraulic fracturing units  12  configured to pump a fracturing fluid into a well at high pressure and high flow rates, so that a subterranean formation fails and begins to fracture in order to promote hydrocarbon production from the well. 
     In some examples, one or more of the hydraulic fracturing units  12  may include directly driven turbine (DDT) pumping units, in which fracturing pumps  18  are connected to one or more gas turbine engines (GTEs)  20  that supply power to the respective fracturing pump  18  for supplying fracturing fluid at high pressure and high flow rates to a formation. For example, a GTE  20  may be connected to a respective fracturing pump  18  via a reduction transmission connected to a drive shaft, which, in turn, is connected to an input shaft or input flange of a respective fracturing pump  18 , which may be a reciprocating pump. Other types of GTE-to-fracturing pump arrangements are contemplated. 
     In some examples, one or more of the GTEs  20  may be a dual-fuel or bi-fuel GTE, for example, capable of being operated using of two or more different types of fuel, such as a gaseous fuel, for example, natural gas, and a fluid fuel, for example, diesel fuel, although other types of fuel are contemplated. For example, a dual-fuel or bi-fuel GTE may be capable of being operated using a first type of fuel, a second type of fuel, and/or a combination of the first type of fuel and the second type of fuel. For example, the fuel may include compressed natural gas (CNG), natural gas, field gas, pipeline gas, methane, propane, butane, and/or liquid fuels, such as, for example, diesel fuel (e.g., #2 Diesel), bio-diesel fuel, bio-fuel, alcohol, gasoline, gasohol, aviation fuel, and other fuels as will be understood by those skilled in the art. Gaseous fuels may be supplied by CNG bulk vessels, a gas compressor, a liquid natural gas vaporizer, line gas, and/or well-gas produced natural gas. Other types and sources of fuel and associated fuel supply sources are contemplated. The one or more GTEs  20  may be operated to provide horsepower to drive via a transmission one or more of the fracturing pumps  18  to safely and successfully fracture a formation during a well stimulation project or fracturing operation. Types of prime movers other than GTEs also are contemplated. 
     Although not shown in  FIG.  1   , as will be understood by those skilled in the art, the hydraulic fracturing system  16  may include a plurality of water tanks for supplying water for a fracturing fluid, one or more chemical tanks for supplying gels or agents for adding to the fracturing fluid, and a plurality of proppant tanks (e.g., sand tanks) for supplying proppants for the fracturing fluid. The hydraulic fracturing system  16  may also include a hydration unit for mixing water from the water tanks and gels and/or agents from the chemical tank to form a mixture, for example, gelled water. The hydraulic fracturing system  16  may also include a blender, which may receive the mixture from the hydration unit and proppants via conveyers from the proppant tanks. The blender may mix the mixture and the proppants into a slurry to serve as fracturing fluid for the hydraulic fracturing system  16 . Once combined, the slurry may be discharged through low-pressure hoses, which convey the slurry into two or more low-pressure lines in a frac manifold  22 , as shown in  FIG.  1   . Low-pressure lines in the frac manifold  22  feed the slurry to the plurality of fracturing pumps  18  shown in  FIG.  1    through low-pressure suction hoses. 
       FIG.  1    shows an example fuel delivery system  10  associated with a plurality, or fleet, of example hydraulic fracturing units  12  according to embodiments of the disclosure, although fewer or more hydraulic fracturing units  12  are contemplated. In the example shown, each of the plurality of hydraulic fracturing units  12  includes a GTE  20 . Each of the GTEs  20  supplies power for each of the hydraulic fracturing units  12  to operate a respective fracturing pump  18 . 
     The fracturing pumps  18  are driven by the GTEs  20  of the respective hydraulic fracturing units  12  and discharge the slurry (e.g., the fracturing fluid including the water, agents, gels, and/or proppants) at high pressure and/or a high flow rates through individual high-pressure discharge lines  24  into two or more high-pressure flow lines  26 , sometimes referred to as “missiles,” on the frac manifold  22 . The flow from the flow lines  26  is combined at the frac manifold  22 , and one or more of the flow lines  26  provide flow communication with a manifold assembly, sometimes referred to as a “goat head.” The manifold assembly delivers the slurry into a wellhead manifold, sometimes referred to as a “zipper manifold” or a “frac manifold.” The wellhead manifold may be configured to selectively divert the slurry to, for example, one or more well heads via operation of one or more valves. Once the fracturing process is ceased or completed, flow returning from the fractured formation discharges into a flowback manifold, and the returned flow may be collected in one or more flowback tanks. 
     As shown in the detailed schematic view of an example system  28  for supplying primary fuel and secondary fuel to an example internal combustion engine  30  according to embodiments of the disclosure, one or more of the hydraulic fracturing units  12  also may include hydraulic auxiliary components  32  and electrical auxiliary components  34  for operating auxiliary components of the respective hydraulic fracturing unit  12 , which may facilitate operation of the hydraulic fracturing unit  12 . For example, the hydraulic auxiliary components  32  may be configured to supply hydraulic power for operation of hydraulic circuits on-board the hydraulic fracturing unit  12 , as will be understood by those skilled in the art, including, for example, a hydraulic fluid reservoir, one or more hydraulic pumps for providing the hydraulic circuits with power, one or more flow control valves, metering valves, or check valves, and/or one or more hydraulic actuators, such as hydraulic motors and hydraulic cylinders for preforming functions associated with operation of the hydraulic fracturing unit  12 . The electrical auxiliary components  34  may include one or more electrical power sources to provide electrical power for operation of electrical circuits (e.g., an electrical power generation device, batteries, solar panels, etc.), component controllers, instrumentation, sensors, and/or one or more electric actuators, such as electric motors and linear actuators, as will be understood by those skilled in the art. Other hydraulic and/or electrical components are contemplated. 
     In the example shown in  FIG.  1   , one or more of the components of the hydraulic fracturing system  16  may be configured to be portable, so that the hydraulic fracturing system  16  may be transported to a well site, assembled, operated for a relatively short period of time, at least partially disassembled, and transported to another location of another well site for use. Each of the fracturing pumps  18  and GTEs  20  of a respective hydraulic fracturing unit  12  may be connected to (e.g., mounted on) a chassis. In some examples, the chassis may include a platform or trailer (e.g., a flat-bed trailer) and/or a truck body to which the components of a respective hydraulic fracturing unit  12  may be connected. For example, the components may be carried by trailers and/or incorporated into trucks, so that they may be easily transported between well sites. 
     As shown in  FIG.  1   , the example fuel delivery system  10  may include a plurality of fuel line connection assemblies  14 , for example, for facilitating the supply of primary fuel from a primary fuel source  36  to each of the GTEs  20  of the hydraulic fracturing system  16 . In some embodiments, for example, as shown in  FIG.  1   , one or more of the fuel line connection assemblies  14  may include a manifold line  38  providing fluid flow between the primary fuel source  36  and the respective hydraulic fracturing units  12 . 
     In the example shown in  FIG.  1   , the fuel delivery system  10  includes two hubs  40   a  and  40   b  (e.g., fuel hubs). A first one  40   a  of the hubs  40   a ,  40   b  is connected to the primary fuel source  36  via a first fuel line  42   a , and a second hub  40   b  is connected to the primary fuel source  36  via a second fuel line  42   b . The first hub  40   a  may supply primary fuel to one or more (e.g., each) of the GTEs  20  of a first bank  44   a  of hydraulic fracturing units  12 , and the second hub  40   b  may supply primary fuel to one or more (e.g., each) of the GTEs  20  of a second bank  44   b  of hydraulic fracturing units  12 . Fewer (zero or one), or more, than two hubs are contemplated. 
     For example, as shown in  FIG.  1   , the fuel delivery system  10  may include a fuel line connection assembly  14  associated with each of the hydraulic fracturing units  12 . In the example configuration shown in  FIG.  1   , each of the hydraulic fracturing units  12  of the first bank  44   a  may be in fluid communication with the primary fuel source  36  via the first fuel line  42   a , the first hub  44   a , and a respective one of the manifold lines  38  providing fluid flow between the first hub  40   a  and each of the respective hydraulic fracturing units  12 . 
     As shown in the detailed schematic view in  FIG.  1    of the example system  28  for supplying primary fuel and secondary fuel to an example internal combustion engine  30 , a fuel distribution line  46  may be connected to the manifold line  38  to provide fluid flow between the manifold line  38  and the GTE  20 . In some examples, a fuel valve  48  may be provided in the fuel distribution line  46  to control the flow of primary fuel to the GTE  20 . In some examples, the system  28  may also include a filter  50  disposed in the fuel distribution line  46  between the manifold line  36  and the GTE  20  and configured to filter one or more of particulates or liquids from primary fuel flowing to the GTE  20 . In some examples, the filter  50  may include a first filter configured to remove particulates from primary fuel supplied to the GTE  20  and a second filter (e.g., a coalescing filter) configured to remove liquids from the fuel distribution line  46  before primary fuel reaches the GTE  20 . This may improve performance of the GTE  20  and/or reduce maintenance and/or damage to the GTE  20  due to contaminants in the fuel as will be understood by those skilled in the art. 
     The example system  28  shown in  FIG.  1    also includes a first manifold  52  positioned to provide fluid flow from the primary fuel source  36  of primary fuel to the internal combustion engine  30 . In some examples, and as shown in  FIG.  1   , the internal combustion engine  30  may be connected to the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34  to supply mechanical power to operate the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 , as explained in more detail herein with respect to  FIG.  2   . 
     As shown in  FIG.  1   , a primary valve  54  may be provided in the first manifold  52  and may be configured to control the flow of primary fuel from the primary fuel source  36  to the internal combustion engine  30 . The system  28  also may include a filter  56  disposed in the first manifold  52  between the manifold line  36  and the internal combustion engine  30  and configured to filter one or more of particulates or liquids from primary fuel flowing to the internal combustion engine  30 . In some examples, the filter  56  may include a first filter configured to remove particulates from primary fuel and a second filter (e.g., a coalescing filter) configured to remove liquids from the first manifold  52  before primary fuel reaches the internal combustion engine  30 . This may improve performance of the internal combustion engine  30  and/or reduce maintenance and/or damage to the internal combustion engine  30  due to contaminants in the fuel, for example. In some embodiments, the system  28  for supplying primary fuel and secondary fuel also may include a pressure regulator  58  disposed in the first manifold  52  between, for example, the filter  56  and the primary valve  54  and configured to control pressure of the primary fuel in the first manifold  52 . As explained in more detail herein with respect to  FIG.  2   , this example arrangement may facilitate operation of the internal combustion engine  30  using the primary fuel from the primary fuel source  36  shared with the GTE  20  for operation. 
     As shown in  FIG.  1   , the example system  28  shown also includes a second manifold  60  positioned to provide fluid flow from a secondary fuel supply  62  of secondary fuel to the internal combustion engine  30 . For example, the system  28  also may include a fuel pump  64  configured to draw and/or pump secondary fuel from the secondary fuel supply  62  through the second manifold  60  to the internal combustion engine  30 . Some embodiments also may include a secondary valve  66  disposed in the secondary manifold  60  configured to control the flow of secondary fuel from the secondary fuel supply  62  to the internal combustion engine  30 . The system  28  also may include a filter  68  disposed in the second manifold  60  between the fuel pump  64  and the secondary valve  66  and configured to filter one or more of particulates or liquids from secondary fuel flowing to the internal combustion engine  30 . In some embodiments, the filter  68  may include a first filter configured to remove particulates from secondary fuel and a second filter (e.g., a coalescing filter) configured to remove liquids from the second manifold  60  before secondary fuel reaches the internal combustion engine  30 . This may improve performance of the internal combustion engine  30  and/or reduce maintenance and/or damage to the internal combustion engine  30  due to contaminants in the fuel as will be understood by those skilled in the art. 
     As shown in  FIG.  1   , the system  28 , in some embodiments, still also may include a controller  70  in communication with the primary valve  54 , the fuel pump  64 , and/or the secondary valve  66  and configured to control the flow of primary fuel from the primary fuel source  36  and secondary fuel from the secondary fuel supply  62  to the internal combustion engine  30 . For example, the controller  70  may be configured to receive one or more signals indicative of a hydraulic power load on the internal combustion engine  30  and/or an electric power load on the internal combustion engine  30 . In some examples, the one or more signals indicative of operation of the hydraulic auxiliary components  32  may include one or more signals generated by one or more sensors associated with the hydraulic auxiliary components  32 . In some examples, the one or more signals indicative of operation of the electrical auxiliary components  34  may include one or more signals generated by one or more sensors associated with the electrical auxiliary components  34 . For example, operation of the hydraulic auxiliary components  32 , supplied with power by the internal combustion engine  30 , and/or operation of the electrical auxiliary components  34 , supplied with power by the internal combustion engine  30 , generate a power load on the internal combustion engine  30 , and the internal combustion engine  30  responds to changes in the power load to meet the power demands of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 . 
     In some examples, the controller  70  may determine a total power load on the internal combustion engine  30 , for example, based at least in part on the one or more signals indicative of the hydraulic power load on the internal combustion engine  30  and/or the electric power load on the internal combustion engine  30 . Based at least in part on the total power load, the controller  70  may also determine a first amount of primary fuel to supply to the internal combustion engine  30  and a second amount of secondary fuel to supply to the internal combustion engine  30 . Based at least in part on this determination of the total power load, the controller  70  may be configured to cause the primary valve  54 , associated with the flow of primary fuel to the internal combustion engine  30 , the fuel pump  64 , and/or the secondary valve  66 , associated with the flow of secondary fuel to the internal combustion engine  30 , to operate to supply the first amount of primary fuel and the second amount of secondary fuel to the internal combustion engine  30 . 
     In this example manner, the system  28  may provide fuel for operation from two (or more) different fuel sources to the internal combustion engine  30  for operation. In some examples, the primary fuel may be a gaseous fuel, such as, for example, compressed natural gas (CNG), natural gas, field gas, pipeline gas, methane, propane, and/or butane as will be understood by those skilled in the art. Gaseous fuels may be supplied by CNG bulk vessels, a gas compressor, a liquid natural gas vaporizer, line gas, and/or well-gas produced natural gas. In some examples, the primary fuel may be provided by the primary fuel source  36 , which, in some examples, is the same source of the primary fuel supplied to the GTE  20 . The secondary fuel, in some examples, may be a liquid fuel, such as, for example, diesel fuel (e.g., #2 Diesel), bio-diesel fuel, bio-fuel, alcohol, gasoline, gasohol, aviation fuel, and other fuels as will be understood by those skilled in the art. The secondary fuel may be supplied by the secondary fuel supply  62 , which may be a fuel tank associated with the hydraulic fracturing unit  12  to which the internal combustion engine  30  is connected. 
     Thus, in some examples, the system  28  may be configured to supply both gaseous fuel and liquid fuel to the internal combustion engine  30  for operation. Some examples of the internal combustion engine  30  may be a reciprocating-piston diesel engine, or reciprocating-piston compression-ignition engine, which may be configured to operate using the primary fuel (e.g., natural gas), the secondary fuel (e.g., diesel fuel), or a combination of the primary fuel and secondary fuel. In some examples, operation of the internal combustion engine  30  using primary fuel that includes, or is limited to, natural gas may be relatively more cost-effective and/or may result in relatively reduced emissions as compared to operation of the internal combustion engine  30  using secondary fuel that includes, or is limited to, diesel fuel. Thus, during operation in which the internal combustion engine  30  is able to supply a sufficient amount of power using solely the primary fuel (e.g., natural gas) supplied by the primary fuel source  36  to meet the power demands of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 , the system  28  may operate the internal combustion engine  30  using solely the primary fuel supplied by the primary fuel source  36 , for example, to increase efficiencies and/or reduce emissions associated with operation of the internal combustion engine  30 . 
     In some such examples of the internal combustion engine  30 , operation using solely the primary fuel (e.g., natural gas) may result in a relatively reduced maximum power output as compared to operation of the internal combustion engine  30  using the secondary fuel (e.g., diesel fuel). Thus, for operational situations in which operation of the internal combustion engine  30  using solely the primary fuel supplied by the primary fuel source  36  would not result in supplying enough power to the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34  to meet the power demands of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 , the system  28  may be configured to substitute secondary fuel (e.g., diesel fuel) supplied by the secondary fuel supply  62  for at least a portion of the primary fuel (e.g., natural gas) to meet the demands of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 , for example, as explained in more detail herein. In some operational situations, the system  28  may be configured to operate the internal combustion engine  30  using solely secondary fuel supplied by the secondary fuel supply  62 , for example, to achieve a maximum power output of the internal combustion engine  30 . 
     Although not shown in  FIG.  1   , in some embodiments, the GTE  20  may also be configured to operate using two or more different types of fuel. For example, in addition to being configured to operate using primary fuel supplied by the primary fuel source  36  (e.g., natural gas), some examples of the GTE  20  may also be configured to operate using the secondary fuel (e.g., diesel fuel) supplied by the secondary fuel supply  62 , or a combination of the primary fuel and secondary fuel. The secondary fuel supply  62  may be a fuel tank connected to the hydraulic fracturing unit  12  and/or an auxiliary fuel tank or tanker configured to be in flow communication with the hydraulic fracturing unit  12 , the GTE  20 , and the internal combustion engine  30 . Thus, in some examples, as shown, the GTE  20  and the internal combustion engine  30  may share primary fuel supplied by the primary fuel source  36  with the GTE  20  and/or may share secondary fuel supplied by the secondary fuel supply  62  with the GTE  20 . Other types and sources of fuel are contemplated. 
     In some embodiments, the controller  70  may be configured to cause the first amount of primary fuel to decrease relative to the second amount of secondary fuel as the total power load on the internal combustion  30  increases. Because, in some examples, the secondary fuel supplied by the secondary fuel supply  62  may provide relatively more energy per unit mass or volume than the primary fuel supplied by the primary fuel source  36 , as the load increases on the internal combustion engine, the controller  70  may increase the ratio of secondary fuel to primary fuel supplied to the internal combustion engine  30  to meet the increasing power load demand. 
     The controller  70  may, in some examples, may be configured to determine the first amount or primary fuel and the second amount of secondary fuel based at least in part on an efficiency of the primary fuel (e.g., an energy efficiency and/or a financial efficiency associated with the primary fuel) relative to an efficiency of the secondary fuel (e.g., an energy efficiency and/or a financial efficiency associated with the secondary fuel). For example, for operational situations in which operation of the internal combustion engine  30  using a combination of primary fuel and secondary fuel will provide a power output sufficient to meet the combined power demands from the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 , the controller  70  may be configured to determine the first amount of primary fuel and the second amount of secondary fuel that meets the power demands with the highest efficiency. 
     In some examples, the controller  70  may be configured to determine the amount of primary fuel and the amount of secondary fuel for operation based at least in part on efficiency data accessed from a table stored in memory correlating the efficiency of the primary fuel, the efficiency of the secondary fuel, and/or the power output of the internal combustion engine  30  operating using the primary fuel and the secondary fuel. For example, such correlations may be based on calculations according to theoretical, mathematical, and/or scientific determinations as a function of the efficiency of the primary fuel, the efficiency of the secondary fuel, and/or the power output of the internal combustion engine  30  based on the combination of primary fuel and secondary fuel (e.g., a ratio of the amount of the primary fuel to the amount of the secondary fuel). In some examples, such correlations may be empirically-derived and/or estimated based at least in part on historical operation, testing, and/or simulated operation of the internal combustion engine  30 . 
     In some embodiments, the controller  70  may be configured to determine the first amount of primary fuel and the second amount of the secondary fuel for operation of the internal combustion engine  30 , based at least in part on one or more formulas relating the efficiency of the primary fuel, the efficiency of the secondary fuel, and/or the power output of the internal combustion engine using the primary fuel and the secondary fuel. For example, such formulas may be derived according to theoretical, mathematical, and/or scientific determinations relating the efficiency of the primary fuel, the efficiency of the secondary fuel, and/or the power output of the internal combustion engine  30  based on the combination of primary fuel and secondary fuel (e.g., a ratio of the amount of the primary fuel to the amount of the secondary fuel). In some examples, such formulas may be empirically-derived and/or estimated based at least in part on historical operation, testing, and/or simulated operation of the internal combustion engine  30 . During operation according to some examples, the amounts of primary and/or secondary fuel may be determined real-time, during operation of the internal combustion engine  30 , for example, depending on the total power demand for operation of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 . 
     According to some embodiments, the controller  70  may be configured to determine first expected emissions generated during operation of the internal combustion engine  30  using the first amount of primary fuel and/or second expected emissions generated during operation of the internal combustion engine  30  using the second amount of secondary fuel. For example, emissions generated by operation of the internal combustion engine  30  using the primary fuel may differ from emissions generated by operation of the internal combustion engine  30  using secondary fuel. Thus, in some examples, the controller  70  may be configured to estimate or determine first expected emissions generated during operation of the internal combustion engine  30  using the first amount of primary fuel and/or second expected emissions generated during operation of the internal combustion engine  30  using the second amount of secondary fuel. Based at least in part on this/these determination(s), the controller  70  may be configured to optimize the ratio of the first amount of primary fuel to the second amount of secondary fuel to achieve a desired emissions level (e.g., a lowest emissions level overall or per unit power output) during operation of the internal combustion engine  30 . 
     In some embodiments, the controller  70  may be configured to determine the first amount of primary fuel and the second amount of secondary fuel based at least in part on emissions data from a table correlating the first expected emissions from operation using primary fuel, the second expected emissions using secondary fuel, and/or the power output of the internal combustion engine  30  operating using the first amount of primary fuel and the second amount of secondary fuel. For example, such correlations may be based on calculations according to theoretical, mathematical, and/or scientific determinations as a function of the expected emissions due to operation using the primary fuel, the expected emissions due to operation using the secondary fuel, and/or the power output of the internal combustion engine  30  based on the combination of primary fuel and secondary fuel (e.g., a ratio of the amount of the primary fuel to the amount of the secondary fuel). In some examples, such correlations may be empirically-derived and/or estimated based at least in part on historical operation, testing, and/or simulated operation of the internal combustion engine  30 . 
     In some embodiments, the controller  70  may be configured to determine the first amount of primary fuel and second amount of the secondary fuel for operation of the internal combustion engine  30 , based at least in part on one or more formulas relating the expected emissions from operation using the primary fuel, the expected emissions from operation using the secondary fuel, and/or the power output of the internal combustion engine using the primary fuel and the secondary fuel. For example, such formulas may be derived according to theoretical, mathematical, and/or scientific determinations relating the expected emissions from operation using the primary fuel, the expected emissions from operation using the secondary fuel, and/or the power output of the internal combustion engine  30  based on the combination of primary fuel and secondary fuel (e.g., a ratio of the amount of the primary fuel to the amount of the secondary fuel). In some examples, such formulas may be empirically-derived and/or estimated based at least in part on historical operation, testing, and/or simulated operation of the internal combustion engine  30 . During operation according to some examples, the amounts of primary and/or secondary fuel may be determined real-time, during operation of the internal combustion engine  30 , for example, depending on the total power demand for operation of the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 . 
     In still other embodiments, the controller  70  may be configured to cause the internal combustion engine  30  to operate according to two or more phases, depending at least in part on the total power load from the hydraulic auxiliary components  32  and/or the electrical auxiliary components  34 . For example, the two or more phases may include a first phase during which operation of the internal combustion engine  30  using a combination of the first amount of primary fuel and the second amount of secondary fuel provides a power output at least equal to the total power load. The first amount of primary fuel may have an ability, when combusted, to produce a specific amount of energy, and similarly, the second amount of the secondary fuel may have an ability, when combusted, to produce a specific amount of energy. In some examples, according to operation during the first phase, the first amount of primary fuel and the second amount of secondary fuel include an amount of energy at least equal to the total power load. For example, during the first phase, if the internal combustion engine  30  is able to supply a sufficient amount of power without using solely the secondary fuel to meet the total power demand, the controller  70  may cause the internal combustion engine  30  to substitute an amount of primary fuel for an amount of the secondary fuel while still providing an amount of power sufficient to meet the total power load demanded, for example, as described herein. 
     In some embodiments, the two or more phases may include a second phase, for example, when the total power load is greater than a maximum amount of power output the internal combustion engine  30  is capable of producing using a combination of the primary fuel and the secondary fuel. In some such examples, the controller  70  may be configured to cause operation of the internal combustion engine using solely secondary fuel, so that the internal combustion engine  30  may operate to provide an amount of power to meet the total power load demanded and/or provide its maximum power output. 
     In some embodiments of the system  28 , during operation of the internal combustion engine  30  according to the first phase, the controller  70  may be configured to determine the first amount of primary fuel and the second amount of secondary fuel based at least in part on a first efficiency of the primary fuel, a second efficiency of the secondary fuel, a first expected emissions generated during operation of the internal combustion engine using the first amount of primary fuel, and/or a second expected emissions generated during operation of the internal combustion engine  30  using the second amount of secondary fuel. In some examples, the effect of the efficiencies and/or emissions may be weighted, for example, to cause the effects to have a different level of influence on the outcome of the determination. For example, it may be desirable to achieve an operational efficiency of the internal combustion engine  30  that is above a threshold, and thus, the effects of the efficiencies of the primary and secondary fuel may be weighted relatively more heavily in the determination than the effects of emissions. Under some circumstances, the effect on emissions may be weighted relatively more heavily, for example, to reduce emissions to a level below a predetermined threshold, for example, to comply with government standards or regulations associated with emissions due to operation of the internal combustion engine  30 . 
       FIG.  2    is a schematic view of an example system  28  for supplying primary fuel and secondary fuel to an internal combustion engine  30  to provide power for example hydraulic auxiliary components  32  and example electrical auxiliary components  34  according to embodiments of the disclosure. As shown in  FIG.  2   , some examples of the internal combustion engine  30  may include a turbocharger  72  including a turbine  74  and a compressor  76  connected to the turbine  74  and configured to be driven by the compressor  76  during operation of the internal combustion engine  30 , thereby increasing the intake pressure of the internal combustion engine  30  during operation to increase power output. For example, the internal combustion engine  30  may include an exhaust system  78 , including an exhaust manifold  80  and an exhaust conduit  82  providing exhaust flow between the exhaust manifold  80  and the turbine  74  of the turbocharger  72 . 
     During operation of the internal combustion engine  30 , exhaust gas generated during combustion flows to the turbine  74  via the exhaust manifold  80  and the exhaust conduit  82 , and energy in the exhaust gas is imparted to the turbine  74 , causing it to spin and drive the compressor  76 , which is in flow communication with an intake conduit  84 , which supplies the compressed air to an intake manifold  86  of the internal combustion engine  30 . Ambient intake air  88  is supplied via an intake  90  and the intake conduit  84  to the compressor  76  for compression. As shown, some examples, of the internal combustion engine  30  include an air filter  92  configured to remove or separate particulates from the air drawn into the intake  90 . 
     As shown in  FIG.  2   , in some embodiments, the system  28  is configured such that the first manifold  52 , which provides fluid flow between the primary fuel source  36  and the internal combustion engine  30  through the primary valve  54 , intersects and feeds the intake conduit  84  upstream of the compressor  76  of the turbocharger  72 , such that the primary fuel mixes with the ambient air in the intake conduit  84  prior to being compressed by the turbocharger  72 . Once compressed by the compressor  76 , the air and primary fuel mixture flows to the intake manifold  86 , where it can be distributed for combustion in the internal combustion engine  30 . 
     As shown, secondary fuel from the secondary fuel supply  62  may be pumped via the fuel pump  64  via the second manifold  60  through the secondary valve  66  to a fuel rail  94  and thereafter injected under pressure via fuel injectors directly into one or more cylinders  96  (e.g., into the combustion chambers) of a cylinder block  98  of the internal combustion engine  30 . When operating using both primary fuel and secondary fuel, the primary fuel entering the intake manifold  86  and the secondary fuel entering the fuel rail  94 , may be combined in the cylinders  96  (e.g., in the combustion chambers) for combustion by the internal combustion engine  30 . By controlling operation of the primary valve  54 , the fuel pump  64 , and/or the secondary valve  66 , the controller  70  is, in some examples, able to cause the internal combustion engine  30  to operate using solely primary fuel, solely secondary fuel, and/or a combination of primary fuel and secondary fuel. As explained previously herein, the controller  70  may be configured change the ratio of the amount of primary fuel to the amount of secondary fuel, for example, based on a load on the internal combustion engine  30 , efficiencies associated with the primary fuel and/or the secondary fuel, and/or expected emissions from operation using the primary fuel and/or the secondary fuel. 
     As shown in  FIG.  2   , the hydraulic auxiliary components  32  may include one or more hydraulic pumps  100  and one or more hydraulic components  102 . For example, the hydraulic auxiliary components  32  may be configured to supply hydraulic power for operation of hydraulic circuits on-board the hydraulic fracturing unit  12  including, for example, a hydraulic fluid reservoir, the one or more hydraulic pumps  100  for providing the hydraulic power to operate one or more of the hydraulic components  102 , which may be incorporated into hydraulic circuits, such as flow control valves, metering valves, check valves, and/or one or more hydraulic actuators, such as hydraulic motors and hydraulic cylinders for preforming functions associated with operation of the hydraulic fracturing unit  12 . Other hydraulic components are contemplated. 
     The example electrical auxiliary components  34  shown in  FIG.  2    includes one or more electric power generation devices  104  and one or more electrical components  106 . For example, the electrical auxiliary components  34  may include one or more electrical power generation devices  104  (e.g., alternators, generators, batteries, solar panels, etc.) for operation of electrical circuits including electrical components  106  associated with operation of the hydraulic fracturing unit  12 , such as component controllers, instrumentation, sensors, and/or one or more electric actuators, such as electric motors and linear actuators. Other electrical components are contemplated. 
       FIG.  3    is a graph  300  showing an example relationship of percentage of primary fuel supplied to operate an internal combustion engine  30  as a function of a percentage of maximum power output by the internal combustion engine  30  as represented by the line  302 , according to an embodiment of the disclosure. As shown in  FIG.  3   , in some examples, the controller  70  may be configured to begin substituting primary fuel for secondary fuel at a power output of about 10 percent of the maximum power output of the internal combustion engine  30 . In some examples, the controller  70  may be configured to begin substituting primary fuel for secondary fuel at a power output ranging from about 10 percent to about 30 percent (e.g., ranging from about 20 percent to about 25 percent) of the maximum power output of the internal combustion engine  30 . 
     As shown in  FIG.  3   , the controller  70  may be configured to increase the amount of substitution of primary fuel for secondary fuel as the power output of the internal combustion engine  30  increases from about 10 percent to about 50 percent of the maximum power output, with the percentage of primary fuel rising to an amount ranging from about 70 percent to about 80 percent. In the example shown, the controller  70  may be configured to substantially maintain the substitution rate of primary fuel for secondary fuel at a range of about 70 percent to about 80 percent at a power output ranging from about 50 percent to about 80 percent of the maximum power output of the internal combustion engine  30  (e.g., from about 50 percent to about 65 percent or 70 percent). Beginning at about 65 percent to about 80 percent of the maximum power output of the internal combustion engine  30 , the controller  70  may be configured to begin reducing the rate of substitution of primary fuel for secondary fuel, and by about 85 percent to about 95 percent of the maximum power output, the controller  70  may be configured to reduce the rate of substitution of primary fuel for secondary fuel to about zero. In some examples of the internal combustion engine  30 , the primary fuel, and the secondary fuel, the internal combustion engine  30  may not be capable of a power output of greater than about 85 percent to about 95 percent of maximum power during operation using any primary fuel, and thus, in some such examples, the controller  70  may be configured to cease substitution of primary fuel for secondary fuel at power outputs greater than about 85 percent to about 95 percent of maximum power, so that the internal combustion engine  30  operates solely using secondary fuel to achieve the desired power output. For example, the primary fuel may not have a sufficient amount of potential energy per unit volume for the internal combustion engine  30  to operate close to its maximum power output, while in contrast, the secondary fuel may have a sufficient amount of potential energy per unit volume for the internal combustion engine  30  to operate close to, or at, its maximum power output. 
     As shown in the example of  FIG.  3   , in instances in which operating the internal combustion engine  30  using primary fuel is relatively more efficient (e.g., with respect to cost) than operating the internal combustion engine  30  using secondary fuel, it may be desirable, with respect to efficiency, to operate the internal combustion engine  30  at a power output ranging from about 40 percent to about 80 percent (e.g., from about 45 percent to about 70 percent) of the maximum power output of the internal combustion engine  30 , such that the amount of primary fuel substituted for secondary fuel is substantially maintained at an amount ranging from about 60 percent to about 80 percent. Different ranges of power output and/or substitution rates of primary fuel for secondary fuel are contemplated, depending, for example, on the internal combustion engine  30 , the primary fuel, and/or the secondary fuel. 
       FIG.  4    is a graph  400  showing an example relationship of efficiency associated with operation of an internal combustion engine  30  as a function of a percentage of maximum power output by the internal combustion engine  30  as represented by the line  402 , according to an embodiment of the disclosure.  FIG.  4    shows a reduction in efficiency as an increase along the Y-axis of the graph  400  as a unit-less magnitude ranging from about 2 to about 7.5. The efficiency may be determined, for example, based at least in part on one or more factors, such as power usage, cost of operation (e.g., including fuel cost), time to delivery of power output, type or types of fuel(s) used for operation, the suitability of the fuel(s) for operation, the completeness of combustion of the fuel(s), the quality of the fuel(s), and/or the emissions generated during combustion of the fuel(s). 
     For example, as shown in  FIG.  4   , a reduction in efficiency may occur as the internal combustion engine  30  increases its power output, shown on the X-axis as a percentage of the maximum power output of the internal combustion engine  30 . Thus, in general, in the example shown, as the power output of the internal combustion engine  30  increases, its efficiency may be thought of as decreasing, for example, because relatively more fuel may be required to operate the internal combustion engine  30  at relatively higher power outputs. This does not preclude the possibility that, in some examples, operation of the internal combustion engine  30  at relatively higher power outputs may be relatively more efficient, for example, due to the power output being a greater percentage of the maximum possible power output due to the potential energy of the fuel or fuels supplied to the internal combustion engine  30  for operation (e.g., due to more complete combustion). 
     In some examples, a reduction in efficiency may occur as the internal combustion engine  30  increases its power output, as shown in  FIG.  4   , which may correlate to an increase in cost of operation of the internal combustion engine  30  due, for example, to the cost of the secondary fuel being relatively more expensive per unit volume than the cost of primary fuel per unit volume. Thus, in general in the example shown, as more primary fuel is substituted for secondary fuel, the reduction in efficiency (e.g., the increase in cost) does not increase as quickly as the internal combustion engine  30  is operated at a higher percentage of its maximum power output and more total fuel is required to produce a greater power output by the internal combustion engine  30 . Thus, although the cost increases due to the increase in power output (e.g., the reduction in efficiency increases), by using a greater percentage of primary fuel, which costs less per unit volume than the secondary fuel in the example, the rate of increase in cost is reduced, with the rate of increase in cost being represented by the slope of the line  402 . 
     In some embodiments, as shown in  FIG.  4   , as the load on the internal combustion engine  30  increases, such that the percentage of the maximum power output of the internal combustion engine  30  at which the internal combustion engine  30  operates increases to meet the increasing load, the efficiency reduction of operation of the internal combustion engine  30  increases (e.g., the cost increases), as shown by the upward trend in line  402  as the power output increases. For example, when the internal combustion engine  30  is operated at a power output ranging from less than about 40 percent of maximum power output to less than about 80 percent of the maximum power output, the internal combustion engine  30  is able to be operated using an increasing percentage of the primary fuel (from less than about 60 percent to about 70 percent primary fuel) and a corresponding decreasing percentage of the secondary fuel. At operation above 80 percent maximum power output, in order to supply a power output sufficient to meet the increasing load on the internal combustion engine  30 , in some embodiments, operation reverts to operation using solely (e.g., 100 percent) the secondary fuel, for example, because the primary fuel does not have sufficient energy to meet the load demands by operating at above 80 percent of maximum power output, for example, as explained with respect to  FIG.  3   . Under these circumstances, according to some embodiments, if use of the secondary fuel for operation is less efficient (e.g., less cost-effective) than use of the primary fuel, the efficiency reduction increases, for example, as shown by the slope of line  402  increasing as the internal combustion engine  30  is operated at a power output above about 75 percent to about 80 percent of the maximum power output of the internal combustion engine  30 . 
       FIG.  5    is a schematic view of another embodiment of a hydraulic fracturing system  16 , including a plurality of hydraulic fracturing units  12  receiving primary fuel from an example primary fuel source  36  according to embodiments of the disclosure. In the example shown in  FIG.  5   , the original source of the primary fuel is a wellhead  500  of a natural gas well located close to the hydraulic fracturing system  16 , which may provide a convenient and/or cost-effective source of the primary fuel. In some such examples, natural gas may flow to a scrubber and filtration system  502  via a first gas fuel line  504  and thereafter flow to the primary fuel source  36  via a second gas fuel line  506 . Thereafter, the primary fuel may flow from the primary fuel source  36  via the first fuel line  42   a  and the second fuel line  42   b , for example, similar to as shown in  FIG.  1   . Other fuel delivery arrangements are contemplated, such as, for example, “daisy-chain” arrangements, “hub-and-spoke” arrangements, combination “daisy-chain” and “hub-and-spoke” arrangements, and/or modifications of such arrangements. 
       FIG.  6    is a block diagram of an example method  600  for supplying primary fuel and secondary fuel to a reciprocating-piston engine according to embodiments of the disclosure, illustrated as a collection of blocks in a logical flow graph, which represent a sequence of operations that may be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described blocks can be combined in any order and/or in parallel to implement the methods. 
       FIG.  6    is a flow diagram of an embodiment of a method  600  for supplying primary fuel and secondary fuel to a reciprocating-piston engine, for example, associated with a hydraulic fracturing unit of a hydraulic fracturing system, according to embodiments of the disclosure. In some examples, the method  600  may be performed semi- or fully-autonomously, for example, via a controller. The method  600  may be utilized in association with various systems, such as, for example, the example system  28  shown in one or more of  FIGS.  1  and  2   . 
     The example method  600 , at  602 , may include determining a total power load on the reciprocating-piston engine due to operation of hydraulic auxiliary components supplied with power by the reciprocating-piston engine and/or electrical auxiliary components supplied with power by the reciprocating-piston engine. For example, a controller may receive one or more signals indicative of operation of one or more of the hydraulic auxiliary components or the electrical auxiliary components, for example, as described previously herein. In some examples, the one or more signals may include one or more signals generated by one or more sensors associated with the hydraulic auxiliary components or the electrical auxiliary components. 
     At  604 , the example method  600  may further include determining a first amount of primary fuel to supply to the reciprocating-piston engine and a second amount of secondary fuel to supply to the reciprocating-piston engine, for example, based at least in part on the total power load. For example, the controller may be configured determine the first amount and the second amount based at least in part on an efficiency of the primary fuel relative to an efficiency of the secondary fuel, for example, as described previously herein. In some examples, the controller may be configured to determine the first amount and the second amount based at least in part on first expected emissions generated during operation of the reciprocating-piston engine using the first amount of primary fuel or second expected emissions generated during operation of the reciprocating-piston engine using the second amount of secondary fuel, for example, as previously described herein. 
     At  606 , the example method  600  may also include causing a primary valve to operate to supply the first amount of primary fuel to the reciprocating-piston engine, for example, based at least in part on the first amount of the primary fuel and the second amount of the secondary. For example, the controller may be configured to cause the primary valve to open and/or meter primary fuel to supply the reciprocating-piston engine, for example, as described previously herein. 
     The example method  600 , at  608 , may further include causing a fuel pump and/or a secondary valve to operate to supply the second amount of secondary fuel to the reciprocating-piston engine, for example, based at least in part on the first amount of the primary fuel and the second amount of the secondary. For example, the controller may be configured to cause the fuel pump and/or the secondary valve to open and/or meter secondary fuel to supply the reciprocating-piston engine, for example, as described previously herein. 
     The example method  600 , at  610 , may also include causing the reciprocating-piston engine to operate according to two or more phases, depending at least in part on the total power load. 
     For example, at  612 , the example method  600  may also include determining whether using a combination of the first amount of primary fuel and the second amount of the secondary fuel provides a power output at least equal to the total power load. For example, the controller may determine whether the primary fuel has enough energy per unit mass to provide an amount of energy sufficient to supply the reciprocating piston-engine to provide a power output at least equal to the total power load. If so, a combination of the primary fuel and secondary fuel may be used to supply the reciprocating-piston engine. 
     If, at  612 , it has been determined that using a combination of the first amount of primary fuel and the second amount of the secondary fuel provides a power output at least equal to the total power load, at  614 , the example method  600  may further include determining the first amount of primary fuel and the second amount of secondary fuel based at least in part on considerations related to efficiency and/or emissions. For example, the considerations may relate to a first efficiency of the primary fuel, a second efficiency of the secondary fuel, a first expected emissions generated during operation of the reciprocating-piston engine using the first amount of primary fuel, and/or a second expected emissions generated during operation of the reciprocating-piston engine using the second amount of secondary fuel. For example, the controller may be configured to access tables and or perform calculations to determine a combination of the first amount of primary fuel and the second amount of secondary fuel to provide a power output sufficient to meet the power demand corresponding to the total power load, for example, as described previously herein. 
     If, at  612 , it has been determined that using a combination of the first amount of primary fuel and the second amount of the secondary fuel will not provide a power output at least equal to the total power load, at  616 , however, the example method  600  further may include operating the reciprocating-piston engine using solely the secondary fuel. For example, as described above, the controller may determine that it is not possible to meet the total power load demand using any of the primary fuel and determine that the reciprocating-piston engine should be operated using solely the secondary fuel, which may produce more power than the primary fuel. 
     It should be appreciated that subject matter presented herein may be implemented as a computer process, a computer-controlled apparatus, a computing system, or an article of manufacture, such as a computer-readable storage medium. While the subject matter described herein is presented in the general context of program modules that execute on one or more computing devices, those skilled in the art will recognize that other implementations may be performed in combination with other types of program modules. Generally, program modules include routines, programs, components, data structures, and other types of structures that perform particular tasks or implement particular abstract data types. 
     Those skilled in the art will also appreciate that aspects of the subject matter described herein may be practiced on or in conjunction with other computer system configurations beyond those described herein, including multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, handheld computers, mobile telephone devices, tablet computing devices, special-purposed hardware devices, network appliances, and the like. 
     The controller  80  can include one or more industrial control systems (ICS), such as supervisory control and data acquisition (SCADA) systems, distributed control systems (DCS), and/or programmable logic controllers (PLCs). For example, the controller  80  may include one or more processors, which may operate to perform a variety of functions, as set forth herein. In some examples, the processor(s) may include a central processing unit (CPU), a graphics processing unit (GPU), both CPU and GPU, or other processing units or components. Additionally, at least some of the processor(s) may possess local memory, which also may store program modules, program data, and/or one or more operating systems. The processor(s) may interact with, or include, computer-readable media, which may include volatile memory (e.g., RAM), non-volatile memory (e.g., ROM, flash memory, miniature hard drive, memory card, or the like), or some combination thereof. The computer-readable media may be non-transitory computer-readable media. The computer-readable media may be configured to store computer-executable instructions, which when executed by a computer, perform various operations associated with the processor(s) to perform the operations described herein. 
     Example embodiments of the controller  70  may be provided as a computer program item including a non-transitory machine-readable storage medium having stored thereon instructions (in compressed or uncompressed form) that may be used to program a computer (or other electronic device) to perform processes or methods described herein. The machine-readable storage medium may include, but is not limited to, hard drives, floppy diskettes, optical disks, CD-ROMs, DVDs, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, flash memory, magnetic or optical cards, solid-state memory devices, or other types of media/machine-readable medium suitable for storing electronic instructions. Further, example embodiments may also be provided as a computer program item including a transitory machine-readable signal (in compressed or uncompressed form). Examples of machine-readable signals, whether modulated using a carrier or not, include, but are not limited to, signals that a computer system or machine hosting or running a computer program can be configured to access, including signals downloaded through the Internet or other networks. 
     Having now described some illustrative embodiments of the disclosure, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the disclosure. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives. Those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the invention are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments of the invention. It is, therefore, to be understood that the embodiments described herein are presented by way of example only and that, within the scope of any appended claims and equivalents thereto, the embodiments of the disclosure may be practiced other than as specifically described. 
     This is a continuation of U.S. Non-Provisional application Ser. No. 17/663,294, filed May 13, 2022, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” which is a continuation of U.S. Non-Provisional application Ser. No. 17/653,893, filed Mar. 8, 2022, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,365,616, issued Jun. 21, 2022, which is a continuation of U.S. Non-Provisional application Ser. No. 17/481,794, filed Sep. 22, 2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,313,213, issued Apr. 26, 2022, which is a divisional of U.S. Non-Provisional application Ser. No. 17/301,241, filed Mar. 30, 2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No. 11,208,880, issued Dec. 28, 2021, which claims priority to and the benefit of, under 35 U.S.C. § 119(e), U.S. Provisional Application No. 62/705,188, filed Jun. 15, 2020, titled “BI-FUEL RECIPROCATING ENGINE TO POWER ONBOARD FRACTURING PUMP AUXILIARY SYSTEMS AND RELATED METHODS,” and U.S. Provisional Application No. 62/704,774, filed May 28, 2020, titled “SYSTEMS AND METHODS FOR SUPPLYING PRIMARY FUEL AND SECONDARY FUEL TO AN INTERNAL COMBUSTION ENGINE OF A FRACTURING UNIT,” the disclosures of which are incorporated herein by reference in their entireties. 
     Furthermore, the scope of the present disclosure shall be construed to cover various modifications, combinations, additions, alterations, etc., above and to the above-described embodiments, which shall be considered to be within the scope of this disclosure. Accordingly, various features and characteristics as discussed herein may be selectively interchanged and applied to other illustrated and non-illustrated embodiment, and numerous variations, modifications, and additions further can be made thereto without departing from the spirit and scope of the present invention as set forth in the appended claims.