Patent Application
20130297181
This disclosure is related to control of an engine using a biodiesel fuel blend.
The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Known internal combustion engines may be configured to operate with compression-ignition (CI) combustion, and are often referred to as diesel or CI engines. CI engines employ fuel that may be derived from petroleum or vegetable oil and animal fat stocks. Fuel derived from petroleum includes long-chain hydrocarbon molecules and is referred herein as diesel fuel. Fuel derived from vegetable oil or animal fat stocks includes long-chain alkyl esters and is referred to herein as biodiesel fuel. CI engines can operate on a 100% diesel fuel. Additionally, CI engines can be configured to operate partially or fully on a biodiesel fuel. A biodiesel blend ratio can be identified. BO fuel is identified as a 100% diesel fuel. 100% BV fuel is identified as 100% biodiesel fuel. xx % BV fuel can be identified as a fuel composition including x % biodiesel fuel and (100%−x %) diesel fuel. For example, 40% BV fuel has a fuel composition including 40% biodiesel fuel and 60% diesel fuel.
Diesel fuel and biodiesel fuel have different physical and chemical properties. Diesel fuel has a higher energy density than biodiesel fuel, whereas biodiesel fuel has higher oxygen content than diesel fuel. As a result, a greater mass of biodiesel fuel must be injected than of diesel fuel under the same circumstances in order to achieve similar combustion characteristics. Injected fuel mass for combustion can be adjusted in response to the biodiesel blend ratio. Further, when fuel is used for purposes other than combustion within the engine, injected fuel mass must be adjusted based upon the biodiesel blend ratio.
Fuel cetane numbers indicate the readiness of a fuel to auto-ignite as measured at in-cylinder temperatures and pressures. One known method of measuring cetane number is ASTM D613. Known CI engines operate with a cetane number between 40 and 55. Diesel fuel blended to meet ASTM D975 has a minimum cetane number of 40, with typical values in the 42-45 range. Biodiesel fuel blended according to ASTM D6751 has a minimum cetane number of 40. Biodiesel fuel from vegetable oil has a cetane number range of 46 to 52, and animal-fat-based biodiesels have a cetane number range of 56 to 60. Thus, ignition timing of a cylinder charge may be affected by the biodiesel blend ratio.
One non-combustion use of fuel includes regeneration of a lean NOx trap (LNT). NOx is a component of an exhaust gas flow generated by the engine during combustion. Aftertreatment devices are known to treat NOx within the exhaust gas flow, converting the NOx into other substances to be expelled with the exhaust. A LNT stores NOx molecules during lean engine operations and releases and reduces the stored NOx during rich engine operations. Known LNTs have a finite NOx storage capacity and require periodic regeneration, which may include a fuel rich pulse. It is desirable to control regeneration events to provide emission control and minimize fuel consumption.
A method for operating a compression-ignition engine includes controlling an engine fueling, a compressor boost pressure, and an EGR content in a cylinder charge to maintain engine operation in response to a biodiesel blend ratio of a biodiesel fuel blend.
One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:
Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,
The engine 10 includes sensors to monitor engine operation, and actuators which control engine operation. The sensors and actuators are signally and operatively connected to control module 5. The actuators are installed on the engine and controlled by the control module 5 in response to operator inputs to achieve various performance goals. A fuel injection system including a plurality of direct-injection fuel injectors 12 fluidly coupled either directly or via a common-rail fuel distribution system to a pressurized fuel distribution system including a high-pressure fuel pump 52. The fuel pump 52 may be controlled to control fuel pressure 53. The fuel injectors 12 directly inject fuel into each of the combustion chambers 34 to form a cylinder charge in response to an injector control signal 13 from the control module 5. The fuel injectors 12 are individually supplied with pressurized fuel, and have operating parameters including a minimum pulsewidth and an associated minimum controllable fuel flow rate, and a maximum fuel flow rate. An exhaust gas recirculation (EGR) system includes a flow channel for directing flow of externally recirculated exhaust gas between the exhaust manifold 58 and the intake manifold 56, an intercooler 57 and an EGR valve 32 that is controlled via control signal 33 from the control module 5. An intake air compressor system 38 is configured to control flow of intake air to the engine 10 in response to a compressor boost command 39. The intake air compressor system 38 boosts a supply of intake air into the engine to increase engine mass airflow and thus increase engine power, including increasing intake air pressure to greater than ambient pressure. In one embodiment the intake air compressor system 38 is a variable-geometry turbocharger (VGT) system that includes a turbine device located in the exhaust gas stream rotatably coupled to a compressor device that is configured to increase flow of engine intake air. Alternatively, the intake air compressor system 38 may include a supercharger device or another turbocharger device. An air intercooler device 16 may be fluidly located between the intake air compressor 38 and the engine intake manifold 56. An electronically-controlled throttle valve 14 controls throttle opening and thus flow of intake air into the intake system of the engine in response to a throttle control signal (ETC) 15. A glow-plug may be installed in each of the combustion chambers 34 for increasing in-cylinder temperature during engine starting events at cold ambient temperatures. The engine 10 may be equipped with a controllable valvetrain configured to adjust openings and closings of intake and exhaust valves of each of the cylinders, including any one or more of valve timing, phasing (i.e., timing relative to crank angle and piston position), and magnitude of lift of valve openings.
The sensors described herein are configured to monitor physical characteristics and generate signals that correlate to engine, exhaust gas, and ambient parameters. A crank sensor interacts with a multi-tooth target wheel attached to the crankshaft to monitor engine crank position and engine speed (RPM) 25. A combustion pressure sensor 30 is configured to monitor cylinder pressure 31, from which a mean-effective pressure or another suitable combustion parameter may be determined. The combustion pressure sensor 30 may be non-intrusive, including a force transducer having an annular cross-section that is installed into the cylinder head at an opening for a glow-plug and having an output signal that is proportional to cylinder pressure. The pressure sensor 30 includes a piezo-ceramic or other suitable monitoring device. A mass air flow (MAF) sensor 18 monitors mass air flow 19 of fresh intake air. A coolant sensor 36 monitors engine coolant temperature 35. A manifold absolute pressure (MAP) sensor 26 monitors intake manifold absolute pressure 27 and ambient barometric pressure. A manifold air temperature (MAT) sensor 28 monitors intake manifold air temperature 29. Exhaust gas sensors 40 and 42 monitor states 41 and 43 respectively, of one or more exhaust gas parameters, e.g., air/fuel ratio, and exhaust gas constituents, and may be used as feedback for control and diagnostics. Other sensors and monitoring schemes may be employed for purposes of control and diagnostics. Operator input in the form of an output torque request 55 may be obtained through an operator interface system 54 that preferably includes an accelerator pedal and a brake pedal, among other devices. Each of the aforementioned sensors is signally connected to the control module 5 to provide signal information which is transformed to information representative of the respective monitored parameter. It is understood that this configuration is illustrative, not restrictive, including the various sensors being replaceable with functionally equivalent devices and algorithms.
The control module 5 executes routines stored therein to control the aforementioned actuators to control engine operation, including throttle position, fuel injection mass and timing, EGR valve position to control flow of recirculated exhaust gases, compressor boost, glow-plug operation, and control of intake and/or exhaust valve timing, phasing, and lift on systems so equipped. The control module 5 is configured to receive the operator inputs 54 to determine the output torque request 55 and receive signal inputs from the aforementioned sensors to monitor engine operation and ambient conditions. The engine 10 is configured to generate output torque in response to the output torque request 55, including operating over a broad range of temperatures, cylinder charge (air, fuel, and EGR) and injection events. The methods described herein are particularly suited to application on direct-injection compression-ignition engines operating lean of stoichiometry.
Control module, module, control, controller, control unit, processor and similar terms mean any suitable one or various combinations of one or more of Application Specific Integrated Circuit(s) (ASIC), electronic circuit(s), central processing unit(s) (preferably microprocessor(s)) and associated memory and storage (read only, programmable read only, random access, hard drive, etc.) executing one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, appropriate signal conditioning and buffer circuitry, and other suitable components to provide the described functionality. Software, firmware, programs, instructions, routines, code, algorithms and similar terms mean any controller executable instruction sets including calibrations and look-up tables. The control module 5 has a set of control routines executed to provide the desired functions. The routines are preferably executed during preset loop cycles. Routines are executed, such as by a central processing unit, and are operable to monitor inputs from sensing devices and other networked control modules, and execute control and diagnostic routines to control operation of actuators. Loop cycles may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, routines may be executed in response to occurrence of an event.
The blend ratio subroutine 110 is executed to determine a magnitude of the biodiesel blend ratio 111 using suitable monitoring and analytical schemes. A first exemplary method to determine a biodiesel blend ratio based upon an exhaust oxygen fraction and an air/fuel ratio is disclosed in co-pending and commonly assigned U.S. Ser. No. 13/113,177 (Attorney Docket No. P014873), which is incorporated herein by reference. A second exemplary method to determine the biodiesel blend ratio based upon an in-cylinder pressure is disclosed in co-pending and commonly assigned U.S. Ser. No. 12/850,122 (Attorney Docket No. P009553), which is incorporated herein by reference. By directly determining the biodiesel blend ratio, properties of the engine fuel can be estimated or determined from look-up values. The biodiesel blend ratio may be calculated as a volumetric blend ratio or another suitable ratio.
The fueling subroutine 120 uses the output torque request 55, the biodiesel blend ratio 111, and the engine operating parameters 105 to determine and generate outputs including fuel parameters associated with the biodiesel blend ratio 135, a base fueling command 137 and an adjusted fueling command 139, which are provided as inputs to the adaptive controller 140. An engine torque determination scheme 155 analyzes the output torque request 55 to determine an engine torque request 55′. When the powertrain system employs the engine 10 as a single torque-generative device that is coupled to a fixed-gear transmission device, the engine torque request 55′ is set equal to the output torque request 55. When the powertrain system employs the engine 10 as one of a plurality of torque-generative devices that generate tractive torque in response to the output torque request 55 (e.g., in a hybrid powertrain system), the engine torque request 55′ may differ from the output torque request 55, with additional torque generated using other torque-generative devices, e.g., electric motor/generators. The base fueling command 137 is determined in response to the engine torque request 55′, and is an engine fueling command that is determined based upon an amount of 0% BV diesel fuel required to generate engine torque to meet the engine torque request 55′. The base fueling command 137 is adjusted to the adjusted fueling command 139 based upon a lower heating value of the fuel blend, wherein the lower heating value of the fuel blend is determined based upon the biodiesel blend ratio 111.
In operation the fueling subroutine 120 is employed to adapt engine operation in response to the biodiesel blend ratio. The engine torque request 55′, the biodiesel blend ratio 111 and engine parameters 105 are periodically monitored. The engine parameters 105 preferably include MAF 19, MAP 27, MAT 29, cylinder pressure 31, RPM 25, coolant temperature 35, and exhaust gas parameters 41 of air/fuel ratio, NOx, and/or others (122).
Fuel parameters corresponding to the biodiesel blend ratio (BV) 111 of the engine fuel are determined (124). The primary fuel parameter of interest is a fuel heating value ratio (LHVRD/LHVBD), which is a ratio of the energy content of diesel fuel, i.e., 0% BV (LHVBD), in relation to the energy content of the biodiesel fuel blend (LHVBD) with which the engine 10 is presently operating. The fuel heating value ratio may be determined based upon cylinder pressure. Alternatively, the fuel heating value ratio may be determined by monitoring exhaust gas air/fuel ratio and intake air flow, determining a stoichiometric air/fuel ratio of the biodiesel fuel blend, and determining the fuel heating value ratio based upon a ratio of a stoichiometric air/fuel ratio of 0% BV diesel fuel (RD) and the stoichiometric air/fuel ratio of the biodiesel fuel blend BD, hereinafter referred to as a ratio of stoichiometric air/fuel combustion (AFRstRD/AFRstBD). Such methods are known to persons having ordinary skill in the art.
A base engine fueling (Fbase) is calculated in response to the engine torque request 55′ and the aforementioned engine parameters (126). The base engine fueling (Fbase) is a measure of the amount of 0% BV diesel fuel to deliver to the engine to generate torque that is responsive to the engine torque request 55′ taking into account the engine operating parameters 105.
It is determined whether the biodiesel blend ratio (BV) is greater than a threshold blend ratio (BVthr) (128). When the biodiesel blend ratio is less than the threshold blend ratio, the effect of the biodiesel fuel blend upon engine operation is considered relatively minor, and adaptive engine control is not employed (0). Instead, the adjusted engine fueling (Fadj) is set equal to the base engine fueling (Fbase) (132). When the biodiesel blend ratio is greater than the threshold blend ratio (128) (1), the effect of the biodiesel fuel blend upon engine operation is considered sufficient to employ adaptive engine control. The threshold blend ratio BVthr may be any suitable value that accounts for the effect of the biodiesel fuel blend upon engine operation, especially engine output power in response to the engine torque request 55′. In one embodiment the threshold blend ratio BVthr may be 30% BV. Alternatively the threshold blend ratio BVthr may be near 25% BV. The adjusted engine fueling (Fadj) is calculated by multiplying the base engine fueling (Fbase) and the fuel heating value ratio (LHVRD/LHVBD). The adjusted engine fueling may be limited to a maximum value, regardless of the magnitude of the fuel heating value ratio. The fueling subroutine 120 returns control parameters for use by the adaptive controller 140. The preferred control parameters include the engine torque request 55′, the base engine fueling (Fbase) 137, the adjusted engine fueling (Fadj) 139, and fuel parameters 135 including the heating value ratio (LHVRD/LHVBD) and the ratio of stoichiometric air/fuel combustion (AFRstRD/AFRstBD) (134).
The adaptive controller 140 adjusts fuel and EGR content of a cylinder charge and manages compressor boost in response to a biodiesel fuel blend. The adaptive controller includes an adaptive EGR controller 150, an adaptive MAF controller 160, an adaptive fuel rail pressure controller 170, a boost controller 180, and a fuel injection controller 145. As described herein, the adaptive EGR controller 150 generates EGR control signal 33, the adaptive MAF controller 160 generates ETC control signal 15, the adaptive fuel rail pressure controller 170 generates fuel pressure control signal 53, the boost controller 180 generates compressor boost command 39, and the fuel injection controller 145 generates the injector control signal 13. The fuel injection controller 145 employs the adjusted fueling command 139 to determine the injector command 13 including fuel injection timing and pulsewidth commands to deliver a mass of fuel into the combustion chamber 34 in response to the engine torque request 55′, taking into account the fuel pressure control signal 53, the aforementioned fuel parameters 135, and the various engine operating parameters 105. As previously stated, the base fueling command 137 is adjusted to the adjusted fueling command 139 based upon the heating value of the biodiesel fuel blend, wherein the heating value of the biodiesel fuel blend is determined based upon the biodiesel blend ratio 111.
A surge line function 181 is developed for the intake air compressor system 38, including separating operation of the intake air compressor system 38 into areas of stability and instability. The surge line function 181 is graphically depicted with compressor inlet pressure Pa on the y-axis, plotted in relation to engine operation as described herein. The surge line function 181 includes a permissible boost line 182 that divides the compressor operation into a stable area 184 and an unstable area 186. Surging occurs when the compressor operates in the unstable area 186, and is caused by a decrease of the intake air mass flow rate or an increase of the discharge pressure, i.e., the intake manifold pressure. The term surge describes a cyclic flow and back-flow of compressed intake air accompanied by high vibrations, pressure shocks and rapid temperature increase in the compressor. Persistent surging may damage the intake air compressor system 38 or other elements of the engine 10 and shorten the service life thereof.
The surge line function 181 is employed to determine a maximum permissible boost pressure
The permissible boost line 182 depicts the maximum permissible boost pressures
The maximum boost pressure
The permissible boost line 182 depicts the maximum permissible boost pressures
Modified line 192 depicts the modified permissible boost pressures
The first stable area 184′ indicates engine operation wherein the boost pressure Pm, is less than the modified permissible boost pressure
The second stable area 188 indicates engine operation wherein the boost pressure
The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.
