WO2020200486A1

WO2020200486A1 - Single point fuel injection in multi-fuel combustion engines

Info

Publication number: WO2020200486A1
Application number: PCT/EP2019/058735
Authority: WO
Inventors: Marek CAMBAL; David KLIZ; Jan KOVACKA
Original assignee: ComAp a.s.
Priority date: 2019-04-05
Filing date: 2019-04-05
Publication date: 2020-10-08

Abstract

A multi-fuel combustion system includes a primary fuel source, a secondary fuel source, a turbocharger including a compressor and a turbine, a charged-air-cooler positioned downstream of the compressor, at least one engine cylinder, a primary fuel injector for each of the at least one engine cylinder, and at least one secondary fuel injector. Each of the primary fuel injectors is configured to directly inject the primary fuel in a corresponding engine cylinder. The at least one secondary fuel injector is configured to inject the second fuel in an intake manifold downstream of the compressor and charged-air-cooler and upstream of the at least one engine cylinder.

Description

TITLE

SINGLE POINT FUEL INJECTION IN MULTI-FUEL COMBUSTION ENGINES

BACKGROUND

[0001] Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a direct injector for each cylinder. Engines may also use multiple fuel sources, such as a fumigation system that injects fuel upstream of a turbocharger. A typical turbocharged engine system includes a turbocharger with a compressor and turbine and a charged-air-cooler that cools the fuel- air mixture from the compressor before passing the mixture to the engine cylinders.

SUMMARY

[0002] The present disclosure provides new and innovative systems and methods of single point fuel injection for dual-fuel combustion engines. In an example, a multi-fuel combustion system includes a primary fuel source, a secondary fuel source, a turbocharger including a compressor and a turbine, a charged-air-cooler positioned downstream of the compressor, at least one engine cylinder, a primary fuel injector for each of the at least one engine cylinder, and at least one secondary fuel injector. Each of the primary fuel injectors is configured to directly inject the primary fuel in a corresponding engine cylinder. The at least one secondary fuel injector is configured to inject the second fuel in an intake manifold downstream of the compressor and charged-air-cooler and upstream of the at least one engine cylinder. Additionally, the at least one secondary injector is asymmetrically controlled based on at least one engine parameter.

[0003] In an example, a method for operating a multi-fuel combustion engine includes supplying air to a compressor of a turbocharger of the multi-fuel combustion engine. The multi-fuel combustion engine has at least one engine cylinder. The method also includes passing the air from the compressor to an intake manifold of the engine and injecting a first fuel into the intake manifold to mix with the air. The first fuel is injected at an injection point at a first time. Additionally, the first fuel is injected into the intake manifold upstream of the at least one engine cylinder and downstream of the compressor. The first fuel is asymmetrically injected based on at least one engine parameter to provide asymmetric control. The method also includes directly injecting a second fuel into the engine cylinder at a second time such that the first fuel, second fuel and air mix and combust within a cylinder of the at least one engine cylinder.

[0004] In an example, a non-transitory machine-readable medium stores a program, which when executed by a processor causes a controller to supply a peak current to a control valve of an injector. The injector is positioned downstream of a compressor of a turbocharger and upstream of each engine cylinder of an engine. Additionally, the injector is configured to inject a fuel at a single point within an intake manifold of the engine. The non-transitory machine -readable medium also causes the controller to supply a holding current to the injector during an injection period after the control valve opens the injector, and reduce the current supplied to the control valve to a baseline value after the injection period. Additionally, current is supplied to the control valve based on at least one engine parameter to provide asymmetric control.

[0005] Additional features and advantages of the disclosed method and system are described in, and will be apparent from, the following Detailed Description and the Figures. The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the figures and description. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.

BRIEF DESCRIPTION OF THE FIGURES

[0006] Fig. 1 illustrates a block diagram of an example dual-fuel combustion engine system according to an example embodiment of the present disclosure.

[0007] Figs. 2A and 2B illustrate an example of fluid flow in a dual-fuel combustion engine according to an example embodiment of the present disclosure.

[0008] Fig. 3A illustrates an example injector configuration for a dual-fuel combustion engine system according to an example embodiment of the present disclosure.

[0009] Fig. 3B illustrates an example injector configuration for a dual-fuel combustion engine system according to an example embodiment of the present disclosure. [0010] Fig. 3C illustrates an example injector configuration for a dual-fuel combustion engine system according to an example embodiment of the present disclosure.

[0011] Fig. 3D illustrates an example injector configuration for a dual-fuel combustion engine system according to an example embodiment of the present disclosure.

[0012] Fig. 4 illustrates a flow chart of an example method of single point fuel injection according to an example embodiment of the present disclosure.

[0013] Fig. 5 illustrates an example current vs. time graph for pulse width modulation control according to an example embodiment of the present disclosure.

[0014] Figs. 6A-6D illustrate example injection cycles according to example embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0015] Techniques are disclosed for providing single point fuel injection in multi fuel (e.g., dual-fuel) combustion engines. As illustrated in Fig. 1, an internal combustion system 100 (e.g., engine) may include a first fuel source 110 (e.g., gas) and a second fuel source 120 (e.g., diesel). The fuel source(s) may be a storage tank. In an example, the first fuel in the fuel source may be natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane, or hydrogen based fuels. The fuel sources 110, 120 are connected to fuel injector(s) 114, 124 via fuel lines 112, 122. As illustrated in Fig. 1, fuel 102 (e.g., gas) from the first fuel source 110 is injected into intake manifold 130 by fuel injector(s) 114 and fuel 104 (e.g., diesel) from the second fuel source 120 is directly injected into engine cylinder(s) 170 by fuel injector(s) 124. For example, the fuel 104 (e.g., diesel) may be directly injected into the combustion chamber of the engine cylinder(s) 170.

[0016] In an example, air 106 travels through air inlet 132 to a compressor 152 of turbocharger 150, where the air is condensed and pushed to a charged-air-cooler (“CAC”) 160. The CAC 160 cools and further condenses the air, which then travels to the intake manifold 130 (also commonly referred to as a suction manifold) where it is mixed with fuel 102. The air-fuel mixture travels from the intake manifold 130 to the engine cylinder(s) 170 where it is further mixed with directly injected fuel 104 from the second fuel source 120 and combusted. The combustion process creates exhaust 108, which exits the engine cylinder(s) 170 through the exhaust manifold 140 and to the turbine 154 of the turbocharger 150. The exhaust 108 passing through turbine 154 runs the compressor 152. Then, the exhaust 108 exits through exhaust outlet 142.

[0017] The internal combustion system 100 is an example of a dual-fuel combustion engine (e.g., a diesel engine). The dual-fuel combustion engine bums or combusts two different fuels 102, 104 (e.g., gas and diesel) at the same time. For example, the second fuel 104 (e.g., diesel) may be directly injected in the engine cylinder(s) 170 and may be used as the initiator to initiate the combustion of the first fuel 102 (e.g., gas).

[0018] As discussed above, and illustrated in more detail in Figs. 2A and 2B, the first fuel 102 (illustrated as circles in Fig. 2B) is introduced into the intake manifold 130 upstream of an engine cylinder(s) 170 and downstream of a turbocharger 150 and CAC 160 (also commonly referred to as an intercooler or an aftercooler). The compressor 152 and CAC 160 delivers a compressed charge flow of air 106 (illustrated by squares in Fig. 2B) to the suction manifold. In an example, (illustrated in Fig. 2A), an air filter 134 may be positioned along air inlet 132 upstream of the compressor 152 to remove particulate matter from air 106. As illustrated in Fig. 2B, the“squares” representing air 106 appear closer together after exiting the compressor 152 and CAC 160 to indicate that the air 106 is a compressed charge flow. In an example, the air 106 exiting the compressor 152 of the turbocharger 150 travels to the CAC 160 where the air is cooled via any suitable heat exchange process, such as an air-to-water or air-to-air heat exchange process.

[0019] After the fuel injector 114 injects the first fuel 102 into the charged flow of air 106, the charged flow of air 106 and fuel 102 mixture are delivered to the engine cylinder(s) 170. For example, the air- fuel mixture may exit the CAC 160 to the intake manifold 130 of the engine for combustion by one or more cylinders 170 of the engine. The air- fuel mixture may enter one or more engine cylinders 170 through corresponding air intake valves. As the piston 172 is at the bottom of the cylinder 170 during the“induction” phase, the air intake valve opens to allow air or the air-fuel mixture to enter the cylinder 170 from the intake manifold. For example, in a diesel engine, the air 106 and fuel 102 mixture may be introduced into the cylinder 170. Then, the air intake valve is closed (and the exhaust valve remains closed) while the piston rod 174 pushes the piston 172 towards the top of cylinder 170 (during the“compression” phase) and the mixture is compressed. [0020] Within the cylinder(s) 170, a second fuel 104 (illustrated by diamonds in Fig. 2B) is directly injected into the cylinder(s) 170, which may act as an initiator to combust the air-fuel mixture. After the second fuel 104 (e.g., diesel) is injected or sprayed into the cylinder 170, the heat from the compression may cause the mixture (e.g., first fuel 102, second fuel 104 and air 106) to ignite. The expansion of the combustion gases pushes the piston 172 back toward the bottom of the cylinder 170 during the power stroke (e.g., during the“combustion” phase). After the mixture of the first fuel 102, second fuel 104 and air 106 is combusted in the respective cylinder(s) of the engine, an exhaust valve is opened which allows the exhaust gas 108 (illustrated by triangles in Fig. 2B) to outlet into an exhaust manifold 140 where it is delivered to the turbine 154 of the turbocharger 150 to drive the compressor 152 via a rotatable shaft therebetween. Then, the exhaust gas 108 leaves the turbine 154 to an exhaust outlet 142. In another example, spark ignition may be used to ignite the mixture (e.g., first fuel 102, second fuel 104 and air 106), causing combustion.

[0021] Additionally, as illustrated in Fig. 2A, the system may include multiple sensors to monitor flow rates, temperatures, etc. of the system. For example, a boost air temperature sensor 180 may sense and monitor the temperature of the air 106 or air-fuel mixture. Additionally, a knocking sensor 182 may sense vibrations caused by engine knock or detonation. Upon detecting engine knock, the timing of the injection by injector 114 and/or injectors 124 may be adjusted. In another example, the system may include an exhaust temperature sensor 184 to monitor the temperature of the exhaust gas 108.

[0022] The fuel injection or delivery may be based at least partially on outputs from one or more of the sensors. For example, the amount of fuel 102 injected into the intake manifold 130 may be based on one or more of the following measured values: intake air manifold temperature, intake air manifold pressure, exhaust gas temperature (e.g., exhaust gas temperature of each cylinder), exhaust gas temperature after the turbocharger, knocking sensor values and a diesel flow sensor. In an example, the amount of fuel 104 injected into the engine cylinder(s) may be adjusted based on the amount of fuel 102 injected into the intake manifold 130. For example, the total output energy from the engine may be the energy from the first fuel 102 (e.g., gas) plus the energy from the second fuel 104 (e.g., diesel). If the total output energy is to remain the same, an increase in the amount of the first fuel 102 (e.g., gas) injected into the intake manifold 130 may correspond to a decreasing amount of the second fuel 104 (e.g., diesel) directly injected into the engine cylinder(s). Additionally, for high speed engines up to 1800 rotations per minute (“RPM”), an engine speed regulator may regulate the RPM and when the first fuel 102 (e.g., gas) is injected, the engine speed regulator may automatically decrease the amount of the second fuel 104 (e.g., diesel) injected into the engine cylinder(s) to maintain a constant RPM, otherwise the engine may experience an over- speed or an over frequency condition.

[0023] The injector(s) 114 advantageously injects fuel 102 downstream of the turbocharger 150 and the CAC 160 thereby eliminating any damage caused by the fuel 102 within the turbocharger 150 and CAC 160. By injecting the first fuel 102 downstream of both the turbocharger 150 and CAC 160, the system 100 prevents gas from entering the compressor 152 of the turbocharger 150 as well as the CAC 160, which improves the durability, longevity and safety of the system 100. For example, if the first fuel 102 is added upstream of the compressor 152, the fuel 102 may damage the compressor 152. In one example, compressor blades may be damaged due to the impact of the fuel 102 against the compressor blades rotating at high speeds. Additionally, the corrosive nature of the fuel 102 may also cause damage to the internal components of both the turbocharger 150 (e.g., compressor 152) and the CAC 160. Mixing fuel 102 and air 112 (illustrated as squares in Fig. 2B) within the compressor 152 also creates a safety concern as fuel-air mixtures are highly combustible and may combust within the compressor 152 of the turbocharger 150.

[0024] A further advantage of injecting the fuel 102 downstream of the turbocharger 150 and CAC 160 is to prevent buildup of particulate matter (e.g., impurities in the fuel 102) within the turbocharger 150 and/or CAC 160, which also prevents damage to those components caused by the buildup. Furthermore, another advantage of injecting fuel 102 downstream of the turbocharger 150 is to reduce the energy required to compress the air 106 in the compressor 152 of the turbocharger 150. For example, a mixture of fuel 102 and air 106 is heavier and requires more energy to compress than air 106 alone in the compressor 150, which improves the fuel economy of the engine. [0025] In an example, the exhaust outlet 142 may include an aftertreatment system to treat the exhaust gas for emissions prior to being outlet to atmosphere. The aftertreatment system may remove particulates, nitrogen-oxide compounds, and other regulated emissions. In another example, a throttle may be positioned within the intake manifold 130 to regulate the charge flow of fuel 102 and air 106 to the cylinders 170. However, to improve control of the fuel-air mixture, each of the injectors 114 that inject fuel 102 into the intake manifold 130 may include electromagnetic valves associated with the injectors 114. The electromagnetic valves may ensure homogeneity of the fuel-air mixture for different engine arrangements (e.g., engines with one cylinder up to engines with 20 cylinders or engine output power form 20kW up to lOOOkW). The electromagnetic valves may advantageously provide more precise and linear control of flow than other technologies. The mass flow of the fuel-air mixture may be precisely controlled by the opening time of the electromagnetic valves. Conversely, other systems such as fumigation systems typically include a butterfly throttle, which is less precise that the system described herein as the flow follows an“S -curve”.

[0026] As illustrated in Figs. 3A, 3B, 3C and 3D, the injector(s) 114 may inject the first fuel 102 at a single point“P” or region (illustrated by the dashed circle) within the intake manifold 130. By injecting the first fuel 102 at a single point“P”, less injectors 114 and fuel lines 112 are required. For example, some dual-fuel systems may include an additional injector 114 for each engine cylinder to directly inject the first fuel 102 into each engine cylinder 170. The additional components (e.g., injectors 114 and fuel lines 112) results in a more complex and heavier system. In another example, such as a fumigation system, the fuel 102 is introduced upstream or before the turbocharger 150, which may cause damage to the compressor 152 of the turbocharger 150 or to the CAC 160.

[0027] As illustrated in Fig. 3 A, air 106 (illustrated by clear arrows) passes through the compressor 152 and CAC 160 and into the intake manifold 130 where it is mixed with fuel 102 (e.g., gas). The air 106 and fuel 102 mix when the fuel 102 is injected by injector(s) 114 at a single point“P” or region within the intake manifold 130. As illustrated in Fig. 3A, a single injector 114 may be used. In other examples, multiple injectors (e.g., injectors 114A-C) may inject fuel 102 at a single point or region within the intake manifold 130. Then, the air-fuel mixture 105 (illustrated by hatched arrows) flows through the intake manifold 130 to the engine cylinders (e.g., cylinders 170A-D). In the illustrated example, the engine includes four engine cylinders 170A-D, but other cylinder configurations may be used (e.g., 1 cylinder to 20 cylinders). The second fuel 104 (e.g., diesel) may be directly injected into each cylinder 170A-D, where the mixture of the first fuel 102, second fuel 104 and air 106 combust and exit the cylinders 170A-D as exhaust gas 108 (illustrated by solid black arrows). The exhaust gas 108 travels through the exhaust manifold and to the turbine 154 of the turbocharger.

[0028] Fig. 3B illustrates another example configuration with eight cylinders (e.g., cylinders 170A-H) in a“v-type” configuration instead of the inline configuration of Fig. 3 A. Similar to the example of Fig. 3 A, the first fuel 102 is injected at a single point“P” or region in the intake manifold 130. As mentioned above, a single injector 114 may be used or multiple injectors (e.g., injectors 114A-C) may inject fuel 102 into the intake manifold 130. The number of injectors may depend on the capacity of each injector and the requirements of the engine. For example, higher output engines requiring larger fuel capacities may include several injectors 114 to meet the fuel needs of the engine. Additionally, multiple injectors may be used to prevent overheating of the electromagnetic valves. Depending on the flow capacity of the injectors and frequency of use, multiple injectors 114 may be implemented to provide gas flow based on the engine characteristics (e.g., number of cylinders, power output, size, etc.) and product life considerations. For example, depending on the frequency of injections, multiple injectors 114 may be implemented to provide adequate cool down time between injection cycles. In an illustrative example, a combustion engine system that needs two injectors 114 (e.g., 114A and 114B) to satisfy the flow capacity requirements may include a four-injector configuration to reduce overheating and extend the lifetime of the injector system. While two of the injectors 114 are injecting gas (e.g., fuel 102) into the intake manifold 130, the other two injectors 114 are turned off and their associated electromagnetic valves are cooling. Additionally groups of injectors 114 may be used (e.g., three groups of two injectors 114) to further extend the expected life of the system. Alternatively, injectors 114 with higher output may also be used to reduce the injection period or dose period, which may also extend the expected life of the system. [0029] Fig. 3C illustrates another example configuration with eight cylinders (e.g., cylinders 170A-H) with the intake manifold split into two separate banks 136 (e.g., banks 136A-B). Fig. 3C illustrates another“v-type” engine configuration. In an example, injectors 114 may inject fuel 102 in each bank 136 of the intake manifold 130 upstream of the engine cylinders 170. For example, injector 114 or group of injectors (e.g., injectors 114A-D) may inject fuel 102 in a first bank 136A of the intake manifold 130 upstream of engine cylinders (170A-D). Similarly, injector 114 or group of injectors (e.g., injectors 114E-H) may inject fuel 102 in a second bank 136B of the intake manifold 130 upstream of engine cylinders (170E-H).

[0030] In the example illustrated in Fig. 3D, an engine such as the Cummins KTA50 may have four CACs 160A-D for cooling air 106 output by one or more turbochargers 150. Each CAC 160A-D cools air 106 that is directed to a different group of engine cylinders (e.g., cylinders 170A-B form a group, cylinders 170C-D form a group, cylinders 170E-F form a group and cylinders 170G-H form a group). Specifically, CAC 160A sends air 106 to cylinders 170A-B, CAC 160B sends air 106 to cylinders 170C-D, CAC 160C sends air 106 to cylinders 170E-F and CAC 160D sends air 106 to cylinders 170G-H. In an example, there may be a corresponding injector 114 or set of injectors 114 for each CAC 160A-D. Specifically injector(s) 114W correspond to CAC 160A and cylinders 170A-B. Similarly, injector(s) 114X-Z correspond to CAC 160B-D and their respective engine cylinders 170C-H. Injections of fuel 102 (e.g., gas) at each of the four injection points“P” may be independently and separately controlled to balance the thermal efficiency of the engine for each bank of cylinders (e.g., cylinders 170A-D for a first bank and cylinders 170E-H for a second bank) and each side of the engine (e.g., cylinders 170A- B and 170E-F for a left side and cylinders 170C-D and 170G-H for a right side).

[0031] For the“v-type” engine configurations illustrated in Figs. 3B, 3C and 3D, the injectors 114 may be controlled by a single control signal such that the same amount of the first fuel 102 (e.g., gas) is injected into each side or bank of the“v-type” engine. For example, referring to Fig. 3C, with a single control signal, the same amount of fuel 102 (e.g., gas) may be injected by injectors 114A-C and 114D-F so that the same amount of fuel 102 (e.g., gas) is injected into each bank 136A and 136B of the intake manifold 130. [0032] In another example, the control signal may be split such that the injectors for each side or bank of the“v-type” engines are controlled independently and separately. For example, some engine configurations may include multiple turbochargers 150 and air filters 134. In an example, referring to the air manifold and cylinder layout of Fig. 3C, air 106 entering bank 136A may be provided by its own turbocharger 150 and set of air filters 134 while air 106 entering bank 136B may be provided by its own turbocharger 150 and set of air filters 134. However, as discussed above, the air filters 134 may remove particulate matter from air 106. As the particulate matter builds up and dirties the filter 134, the filter 134 may become saturated with particulate matter, which restricts and reduces air flow. If the air filters 134 for bank 136B allow less air 106 to pass to the engine cylinders (e.g., the filters 134 are dirty or more restricted) than the air filters 134 for bank 136A, then there may be less air 106 available for combustion within the engine cylinders (e.g., cylinders 170E-H) associated with bank 136B. The reduced flow or quantity of air 106 in bank 136B may reduce the effectiveness of the burning and ignition process. In this illustrated example, the injectors 114D-F may be controlled such that they inject less fuel into bank 136B to corresponded with the reduced air flow to properly balance the fuel/air ratio with bank 136B to prevent the engine from running too rich.

[0033] Reduced air flow from a clogged or saturated air filter 134 is just one illustrative example of how non-symmetrical or asymmetric injection may be used to adjust fuel injection to optimize engine performance and improve engine life. For example, properly balancing the fuel/air ratio may extend the lifetime of several engine components by preventing overheating or corrosion from either excess air 106 or excess fuel 102 during the combustion process.

[0034] In other examples, non-symmetrical injection may be used depending on the temperature of engine components or cylinders. For example, the amount of fuel 102 (e.g., gas) injected may be modified to reduce the temperature of certain engine cylinders in one bank of a“v-type” engine. Each of the factors that influences the thermal efficiency of a bank or section of cylinders 170 in the engine may be monitored to determine how to independently and separately control injectors 114. Readings from sensors such as intake air manifold temperature, intake air manifold pressure, exhaust gas temperature (e.g., exhaust gas temperature of each cylinder), exhaust gas temperature after the turbocharger, knocking sensor values and a diesel flow sensor may be used to modify the amount of fuel 102 (e.g., gas) injected at a specific injection point. Other examples for using non- symmetric or asymmetric injection may include thermodynamic air flow characteristics, construction differences of turbochargers 150, CAC efficiency, engine intake manifold 130 design, number of CACs 160, etc. By controlling each set of gas injectors independently or separately, the engine may be balanced for thermal efficiency for dual-fuel operation to improve performance and extend engine life.

[0035] Fig. 4 illustrates a flowchart of an example method 400 of single point fuel injection according to an example embodiment of the present disclosure. Although the example method 400 is described with reference to the flowchart illustrated in Fig. 4, it will be appreciated that many other methods of performing the acts associated with the method 400 may be used. For example, the order of some of the blocks may be changed, certain blocks may be combined with other blocks, blocks may be repeated, and some of the blocks described are optional. The method 400 may be performed by processing logic that may comprise hardware (circuitry, dedicated logic, etc.), software, or a combination of both.

[0036] The example method 400 includes supplying air to a compressor of a turbocharger (block 402). In an example, the turbocharger 150 may be a component of a multi-fuel combustion engine system (e.g., system 100) that has at least one engine cylinder 170. The air 106 may be supplied through an air inlet 132, which flows to the compressor 152. The method also includes passing the air from the compressor to an intake manifold of the engine (block 404). For example, the air 106 may be compressed and condensed within compressor 152 and then may flow to an intake manifold 130 of the engine. In another example, the air 106 may be further cooled and condensed by flowing through a CAC 160 prior to entering the intake manifold 130.

[0037] The method 400 also includes injecting a first fuel into the intake manifold to mix with the air (block 406). For example, after entering the intake manifold 130, the first fuel 102 may be injected into the intake manifold 130 to mix with the air 106 to form an air-fuel mixture. In an example, the first fuel 102 is injected at an injection point that is upstream of the at least one engine cylinder 170 and downstream of the compressor 152 and/or CAC 160. The first fuel 102 may be injected non- symmetrically or asymmetrically for different cylinder banks or different sides of the engine by independently and separately controlling fuel injectors 114. For example, fuel injectors 114 may be independently controlled to ensure each cylinder 170 has the proper fuel/air ratio. Next, method 400 includes directly injecting a second fuel into the engine cylinder(s) (block 408). For example, after the air-fuel mixture passes into a cylinder 170 of the at least one engine cylinder 170, a second fuel 104 may be directly injected into the cylinder 170 such that the air-fuel mixture (e.g., first fuel 102 and air 106) mix with the second fuel 104 and combust within the cylinder 170. In an example, the first fuel may be one of natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane, and hydrogen based fuels. Additionally, the second fuel may be diesel, which may act as a combustion initiator for the air-fuel mixture within the engine cylinder.

[0038] By injecting the first fuel 102 (e.g., gas) downstream of both the turbocharger 150 and CAC 160, the method 400 advantageously prevents the first fuel (e.g., gas) from entering the compressor 152 of the turbocharger 150 as well as the CAC 160, which improves the durability, longevity and safety of the multi-fuel combustion engine.

[0039] In an example, the power binary outputs of the injectors 114 may be controlled and adjusted according to the engine requirements using a single point injection of a first fuel 102. Additionally, the electromagnetic valves may be controlled using pulse- width-modulation (“PWM”) control. With PWM control, current sent to the electromagnetic valve may be ramped up to a peak current value for a peak time period to open the electromagnetic valve (See Fig. 5). Then, the current may be reduced to a holding current during the injection or dose period (“PointlnDose”). After the injection or dose period, the current may be reduced to zero or the baseline current to close the electromagnetic valves until the next injection cycle. The time between the start of one injection cycle and the next injection cycle may be referred to in Figs. 6A-6D as “PointlnPeriod”. At the start of the next injection cycle, the current is again ramped up to the peak current value for the peak time period followed by the holding current for the injection or dose time period. In the context of engines, the outputs may be adjusted according to engine type, gas valve type and gas pressure along with overlap timing for more valve control. Additionally, the flow may be controlled as a function of the engine RPM, engine power output, number of engine cylinders, injection period and or overlap timing of injector valves (e.g., injection method or“PointlnMethod”), the peak time, the peak current (e.g., percentage of PWM during peak time), the holding current (e.g., percentage of PWM during the rest of the injection period after peak time is over), the PWM frequency for point injection valve control, and whether the point injection is enabled or disabled (e.g.,“PointlnFunc” enabled or disabled).

[0040] There may be eight adjustable parameters (including rotation, carrier frequency and timing of individual outputs) to control the amount of fuel 102 provided to an engine, for example, by controlling the opening and closing of electromagnetic valves associated with the injectors 114 . In other examples, more or less adjustable parameters may be used to modify injection cycles. The injection period may be modified according to the engine type, gas valve type, gas pressure, overlap timing or a combination thereof. Different division of four timers provides a homogenous gas injection system. The distribution of individual periods in the injection cycle, based on engine parameters and number of injectors are illustrated in Figs. 6A-6D, which show various injection frequency and timing. Additionally, the injection or dose period (“PointlnDose”) and the time between the start of one injection cycle and the next“PointlnPeriod” may be modified according to the engine type, gas valve type, gas pressure, overlap timing or a combination thereof.

[0041] In an example, there are eight PWM binary outputs to control the fuel (e.g., gas) injectors 114. The binary outputs may be split into two groups B09 to B012 and BO 15 to B018. In an example, the groups operate simultaneously and in parallel such that B09 and BO 15 operate together in parallel when more than four valves are used.

[0042] Several ranges, default values, and step sizes are provided below for the various example parameters discussed above. Engine RPM (typical (or normal) range: 0- 3000 RPM) may have a default value of 1500 RPM with a step size of 1 RMP. The engine RPM parameter may be used for injection timing calculations for constant or fixed speed engines. For variable speed engines, the injection timing (“PointlnPeriod”) or injection period (“PointlnDose”) may be determined based on actual real-time engine RPM values instead of a set value. [0043] The number of engine cylinders (typical (or normal) range: 1-20 cylinders) may have a default value of four cylinders with a step size of 1 cylinder. Typically, the more engine cylinders there are, the shorter the injection period. In an example, the period (“PointlnPeriod”) may be calculated based on the“Engine RPM”, the number of engine cylinders (“Cyl No.”) according to the following equation. In the below equation, 85ms may be a maximum time available based on application logic.

120 PointlnMethod / 1 \

PointlnPeriod = - * - - - * — - - * 100

Engine RPM Cyl No. \85 * 10 ³/

[0044] To comply with gas homogeneity, the above equation may be governed by a rule that the gas injection rate will occur as many times (or more times) per engine working cycle as the number of cylinders the engine has. For example, the injection rate may be based on the number of engine cylinders such that the period may be shorter with an increasing number of engine cylinders.

Another parameter is the injection method to determine the injection period and or overlap timing of injector valves (e.g.,“PointlnMethod”). In an example, there may be four different selectable point injection methods including a basic period, a double period, a triple period, and a quadruple period. The basic period may be associated with a single signal“a” that is used for each of the binary outputs. The double period may be associated with the signals“a” and“b”, which may be alternated for the binary outputs (e.g., B09, BOl l, B015 and B017 may receive signal“a” while BO10, B012, B016 and B018 receive signal“b”). The triple period may be associated with signals“a”,“b” and“c”, which may be applied to B09, BO 10 and BOl l and similarly applied to B015, B016 and B017. In the example above, a signal may not be applied to B012 and B018 because the injectors 114 may be included in a rail (e.g., a rail of four injectors) and three injectors 114 of the rail may be used and thus three control signals may be used (e.g., signals“a”,“b” and“c”). The quadruple period may be associated with signals“a”,“b”,“c” and“d”. Each of the different timing options is detailed in the table below. In the table, the signals“a”, “b”,“c” and“d” are assigned to physical outputs for each of the injection methods and timing options defined by the rows“A”,“B”,“C” and“D” (e.g., basic period“A”, double period“B”, triple period“C”, and quadruple period“D”). A rail of injectors 114 may be assembled with one or more injectors 114. For example, a rail may include three injectors 114, four injectors 114, six injectors 114, etc.

[0045] Injection method “A” corresponds to Fig. 6A, injection method “B” corresponds to Fig. 6B, injection method“C” corresponds to Fig. 6C, and injection method “D” corresponds to Fig. 6D. Fig. 6A illustrates the most frequent injection cycles and the shortest injection or dose period. The injections of fuel 102 (e.g., gas) are more frequent, but use smaller or shorter dose injections than the other injection methods illustrated in Figs. 6B-6D. Each group of binary outputs (e.g., B09 to B012 and B014 to B018) may be operating simultaneously in parallel such that B09 and BO 15 have matching operating parameters, BO 10 and BO 16 have matching operating parameters, etc. Injection method “A” illustrated in Fig. 6A includes the same injection dose and period for each group of binary outputs.

[0046] In Fig. 6B, the frequency of injections decreases, but the dose is larger or for longer period of time than injection method“A”. Additionally, injection method“B” has identical injection sequences for B09/B015 and B011/B017. Similarly, injection method“B” has identical injection sequences for BO10/BO16 and B012/B018. The period of injection for injection method“B” is twice as long as that for injection method “A” and thus the injections occur at half the frequency as injection method“A”. Even though the injections are less frequent than in injection method“A”, the injection or dose period is longer than injection method“A” and may result in a similar quantity of fuel 102 (e.g., gas) injected over the same period of time for both injection method“A” and injection method“B”.

[0047] The frequency of injections continues to decrease in Figs. 6C and 6D while the dose period increases per injection. As illustrated in Fig. 6C, the binary outputs B012/B018 are not used. For example, a signal may not be applied to B012 and B018 because the injectors may be included in a rail of four injectors 114, but the fourth injector 114 is not used. Because only three of the four injectors 114 are used, three control signals are used (e.g., signals“a”,“b” and“c”), which correspond to each of the respective three injectors 114. As illustrated in Fig. 6D, several of the injection cycles overlap. For example, before the injection cycle for B09 and BO 15 ends, an injection cycle for BO 10 and BO 16 begins. Additionally, before the injection cycle of BO 10 and BO 16 ends, an injection cycle for BOl 1 and B017 begins and so on.

[0048] Other parameters include the peak time, the peak current, and the holding current. The peak time (typical (or normal) range: 0-10ms) may have a default value of 2ms and step of 0.1ms. The peak time may define the time to ramp up the current from an initial value to the peak current. As discussed above, the current sent to the electromagnetic valve may be ramped up to a peak current value for a peak time period to open the electromagnetic value. By reducing the peak time, the valves may be adapted for faster fuel 102 (e.g., gas) doses as the valves open more quickly. The peak current (typical (or normal) range: 0-100%) with a default value of 80% duty cycle and a step of 1%. In an example, an example current may range between 2A and 16 A, and may be based on an injector’s 114 electric parameters (e.g., coil resistance and inductance) as well as power supply voltage. The peak current is the current value needed to open the electromagnetic valve. Additionally, the holding current (typical (or normal) range: 0-100%) with a default value of 50% duty cycle and a step size of 1%. In an example, an electromagnetic valve may have a coil resistance of 5 ohm and the peak current may be approximately 4.5A and the holding current may be approximately 1.7A. The applied voltage for point injection valve control (typical (or normal) PWM frequency range 1000-3000Hz) may have a default PWM frequency of 1000Hz. The holding current may be applied to the electromagnetic valve after the peak time to ensure that the valve stays open during the injection or dose period (“PointlnDose”).

[0049]

[0050] Another parameter is whether the point injection is enabled or disabled (e.g.,“PointlnFunc” enabled or disabled). When disabled, the point injection function is switched off the engine may operate solely from a second fuel 104 (e.g., diesel). When the point injection is enabled, the dual-fuel engine bums or combusts two different fuels 102, 104 (e.g., gas and diesel) at the same time to achieve several of the advantages described herein.

[0051] In an example, the injection timing (“PointlnPeriod”) may be calculated based on the RPM, the number of engine cylinders (“Cyl No.”), and the number of gas injectors. As discussed above, the RPM may be set or may be variable based on the type of engine. In the equations below, the value“120” represents a calculation of engine camshaft frequency (e.g., RPM/(60*2)) where a working cycle is one-half of a crankshaft rotation (e.g., 60*2=120) and the period is (1 /frequency), which gives us“120/RPM” shown below. Additionally, the value“85” may be the maximum period provided by a hardware timer and a software loop. For example, the value“85” may be a maximum time available based on application logic. Specifically, 85ms may represent a full period.

120 1

PointlnPeriod = - *— - - * (No. of Gas Iniectors) \ms ]

RPM Cyl No. ^{J J J}

120 1 1

PointlnPeriod = - *— - - * (N. of Gas Injectors ) *— * 100 [%]

RPM Cyl No. ^{J J J} 85 ^{L J}

[0052] In an example, for constant or fixed engine speeds of 1500 RPM for a 12- cylinder engine, the“PointlnPeriod” may be 26ms when using four (4) fuel injectors 114. Similarly, the“PointlnPeriod” may be 6.6ms with the same configuration but instead using only a single (1) fuel injector 114.

[0053] In another example, for a variable speed engine with a fixed number of fuel injectors 114 (e.g., four injectors) and 12 cylinders, the“PointlnPeriod” may be 50ms at 800 RPM and 20ms at 2000 RPM. The above examples are provided for illustrative purposes only, various other engine configurations and parameters may be used to determine different injection timing values to safely optimize engine power output.

[0054] The various examples described herein provide improved efficiency compared to traditional fumigation systems. For example, efficiency may be improved between 1 percent and 3 percent depending on the engine size, operating conditions, load and RPM of the engine. In addition to the improved efficiency, the present disclosure also provides improved emissions. [0055] Aspects of the subject matter described herein may be useful alone or in combination with one or more other aspects described herein. In a 1st exemplary aspect of the present disclosure, a multi-fuel combustion system includes a primary fuel source, a secondary fuel source, a turbocharger including a compressor and a turbine, a charged-air- cooler positioned downstream of the compressor, at least one engine cylinder, a primary fuel injector for each of the at least one engine cylinder, and at least one secondary fuel injector. Each of the primary fuel injectors is configured to directly inject the primary fuel in a corresponding engine cylinder. The at least one secondary fuel injector is configured to inject the second fuel in an intake manifold downstream of the compressor and charged- air-cooler and upstream of the at least one engine cylinder. Additionally, the at least one secondary injector is asymmetrically controlled based on at least one engine parameter.

[0056] In a 2nd exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st aspect), the primary fuel is configured to initiate combustion of the secondary fuel within the at least one engine cylinder.

[0057] In a 3rd exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st or 2nd aspect), the primary fuel source is diesel fuel.

[0058] In a 4th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st to 3rd aspects), the secondary fuel source is natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane or hydrogen based fuels.

[0059] In a 5th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st to 4th aspects), the at least one secondary fuel injector includes a single injector configured to inject the secondary fuel at a single point within the intake manifold.

[0060] In a 6th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st to 5th aspects), the multi-fuel combustion system further includes at least one control valve. Each of the at least one secondary fuel injectors is controlled by a corresponding control valve of the at least one control valve. [0061] In a 7th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 6th aspect), the at least one control valve is configured to open its corresponding at least one secondary fuel injector based on a fuel-air mixture flow rate.

[0062] In an 8th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 7th aspect), the fuel- air mixture flow rate is a function of engine RPM, number of engine cylinders, engine power output or a combination thereof.

[0063] In a 9th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st aspect), the at least one secondary fuel injector is controlled by an electromagnetic valve operated via pulse- width-modulation.

[0064] In a 10th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st to 9th aspects), the intake manifold includes a first bank and a second bank.

[0065] In an 11th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 10th aspect), the at least one secondary fuel injector includes a first injector and a second injector. The first injector is configured to inject the secondary fuel in the first bank of the intake manifold and the second injector is configured to inject the secondary fuel in the second bank of the intake manifold.

[0066] In a 12th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 10th aspect), the at least one secondary fuel injector includes a first group of injectors and a second group of injectors. The first group of injectors is configured to inject the secondary fuel in the first bank of the intake manifold and the second group of injectors configured to inject the secondary fuel in the second bank of the intake manifold.

[0067] In a 13th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 1st to 12th aspects), the at least one cylinder is a group of cylinders ranging between three cylinders and ten cylinders. [0068] Aspects of the subject matter described herein may be useful alone or in combination with one or more other aspects described herein. In a 14th exemplary aspect of the present disclosure, a method for operating a multi-fuel combustion engine includes supplying air to a compressor of a turbocharger of the multi-fuel combustion engine. The multi-fuel combustion engine has at least one engine cylinder. The method also includes passing the air from the compressor to an intake manifold of the engine and injecting a first fuel into the intake manifold to mix with the air. The first fuel is injected at an injection point at a first time. Additionally, the first fuel is injected into the intake manifold upstream of the at least one engine cylinder and downstream of the compressor. The first fuel is asymmetrically injected based on at least one engine parameter to provide asymmetric control. The method also includes directly injecting a second fuel into the engine cylinder at a second time such that the first fuel, second fuel and air mix and combust within a cylinder of the at least one engine cylinder.

[0069] In a 15th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 14th aspect), the second fuel is diesel fuel.

[0070] In a 16th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 14th or 15th aspect), the first fuel is natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane or hydrogen based fuels.

[0071] In a 17th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 14th to 16th aspects), a single injector injects the first fuel into the intake manifold.

[0072] In an 18th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 14th to 16th aspects), a group of injectors injects the first fuel into the intake manifold.

[0073] Aspects of the subject matter described herein may be useful alone or in combination with one or more other aspects described herein. In a 19th exemplary aspect of the present disclosure, a non-transitory machine-readable medium stores a program, which when executed by a processor causes a controller to supply a peak current to a control valve of an injector. The injector is positioned downstream of a compressor of a turbocharger and upstream of each engine cylinder of an engine. Additionally, the injector is configured to inject a fuel at a single point within an intake manifold of the engine. The non-transitory machine -readable medium also causes the controller to supply a holding current to the injector during an injection period after the control valve opens the injector, and reduce the current supplied to the control valve to a baseline value after the injection period. Additionally, current is supplied to the control valve based on at least one engine parameter to provide asymmetric control.

[0074] In a 20th exemplary aspect of the present disclosure, which may be used in combination with any one or more of the preceding aspects (e.g., the 19th aspect), the fuel is natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane or hydrogen based fuels.

[0075] It will be appreciated that all of the disclosed methods and procedures described herein can be implemented using one or more computer programs or components. These components may be provided as a series of computer instructions on any conventional computer readable medium or machine -readable medium, including volatile or non-volatile memory, such as RAM, ROM, flash memory, magnetic or optical disks, optical memory, or other storage media. The instructions may be provided as software or firmware, and/or may be implemented in whole or in part in hardware components such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), digital signal processors (DSPs) or any other similar devices. The instructions may be configured to be executed by one or more processors, which when executing the series of computer instructions, performs or facilitates the performance of all or part of the disclosed methods and procedures.

[0076] It should be understood that various changes and modifications to the example embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

Claims

CLAIMS The invention is claimed as follows:

1. A multi-fuel combustion system comprising:

a primary fuel source;

a secondary fuel source;

a turbocharger including a compressor and a turbine;

a charged-air-cooler positioned downstream of the compressor;

at least one engine cylinder;

a primary fuel injector for each of the at least one engine cylinder, wherein each of the primary fuel injectors is configured to directly inject the primary fuel in a corresponding engine cylinder; and

at least one secondary fuel injector configured to inject the second fuel in an intake manifold downstream of the compressor and charged-air-cooler and upstream of the at least one engine cylinder, wherein the at least one secondary injector is asymmetrically controlled based on at least one engine parameter.

2. The multi-fuel combustion system of claim 1, wherein the primary fuel is configured to initiate combustion of the secondary fuel within the at least one engine cylinder.

3. The multi-fuel combustion system of claims 1 or 2, wherein the primary fuel source is diesel fuel.

4. The multi-fuel combustion system of any of claims 1 to 3, wherein the secondary fuel source is one of natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane, and hydrogen based fuels.

5. The multi-fuel combustion system of any of claims 1 to 4, wherein the at least one secondary fuel injector includes a single injector configured to inject the secondary fuel at a single point within the intake manifold.

6. The multi-fuel combustion system of any of claims 1 to 5, further comprising at least one control valve, wherein each of the at least one secondary fuel injectors is controlled by a corresponding control valve of the at least one control valve.

7. The multi-fuel combustion system of claim 6, wherein the at least one control valve is configured to open its corresponding at least one secondary fuel injector based on a fuel-air mixture flow rate.

8. The multi-fuel combustion system of claim 7, wherein the fuel-air mixture flow rate is a function of at least one of engine RPM, number of engine cylinders, and engine power output.

9. The multi-fuel combustion system of claim 1, wherein the at least one secondary fuel injector is controlled by an electromagnetic valve operated via pulse-width- modulation.

10. The multi-fuel combustion system of any of claims 1 to 9, wherein the intake manifold includes a first bank and a second bank.

11. The multi-fuel combustion system of claim 10, wherein the at least one secondary fuel injector includes a first injector and a second injector, the first injector configured to inject the secondary fuel in the first bank of the intake manifold and the second injector configured to inject the secondary fuel in the second bank of the intake manifold.

12. The multi-fuel combustion system of claim 10, wherein the at least one secondary fuel injector includes a first group of injectors and a second group of injectors, the first group of injectors configured to inject the secondary fuel in the first bank of the intake manifold and the second group of injectors configured to inject the secondary fuel in the second bank of the intake manifold.

13. The multi-fuel combustion system of any of claims 1 to 12, wherein the at least one cylinder is a group of cylinders ranging between three cylinders and ten cylinders.

14. A method for operating a multi-fuel combustion engine, comprising:

supplying air to a compressor of a turbocharger of the multi-fuel combustion engine, wherein the multi-fuel combustion engine has at least one engine cylinder;

passing the air from the compressor to an intake manifold of the engine;

injecting a first fuel into the intake manifold to mix with the air, wherein the first fuel is injected at an injection point at a first time, wherein the first fuel is injected into the intake manifold upstream of the at least one engine cylinder and downstream of the compressor, and wherein the first fuel is asymmetrically injected based on at least one engine parameter to provide asymmetric control; and

directly injecting a second fuel into the engine cylinder at a second time such that the first fuel, second fuel and air mix and combust within a cylinder of the at least one engine cylinder.

15. The method of claim 14, wherein the second fuel is diesel fuel.

16. The method of claims 14 or 15, wherein the first fuel is one of natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane, and hydrogen based fuels.

17. The method of any of claims 14 to 16, wherein a single injector injects the first fuel into the intake manifold.

18. The method of any of claims 14 to 16, wherein a group of injectors injects the first fuel into the intake manifold.

19. A non-transitory machine-readable medium storing a program, which when executed by a processor causes a controller to:

supply a peak current to a control valve of an injector, wherein the injector is positioned downstream of a compressor of a turbocharger and upstream of each engine cylinder of an engine, and the injector is configured to inject a fuel at a single point within an intake manifold of the engine;

after the control valve opens the injector, supply a holding current to the injector during an injection period; and

after the injection period, reduce the current supplied to the control valve to a baseline value, wherein current is supplied to the control valve based on at least one engine parameter to provide asymmetric control.

20. The non-transitory machine-readable medium of claim 19, wherein the fuel is one of natural gas, LNG (liquefied natural gas), CNG (compressed natural gas), LPG (liquefied petroleum gas), methane, propane, and hydrogen based fuels.