US20190010858A1

US20190010858A1 - Controlling engine coolant fluid temperature

Info

Publication number: US20190010858A1
Application number: US15/645,281
Authority: US
Inventors: Giacomo Di Lorenzo; Michele BILANCIA; Felix Mauricio Quinones Davila; Nicola Totaro
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2017-07-10
Filing date: 2017-07-10
Publication date: 2019-01-10
Also published as: DE102018116588A1; DE102018116588B4; CN109236452A

Abstract

Examples of techniques for controlling temperature of a coolant fluid at an inlet of an internal combustion engine are disclosed. In one example implementation, a method includes receiving, by a processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine. The method further includes receiving, by a processing device, engine speed data indicating an engine speed of the internal combustion engine. The method further includes calculating, by the processing device, a radiator flow rate to achieve a temperature set-point at an inlet of the engine based at least in part on the total fuel burned data and the engine speed data. The method further includes adjusting, by the processing device, a radiator flow based at least in part on the radiator flow rate.

Description

INTRODUCTION

The present disclosure relates generally to internal combustion engines and more particularly to controlling temperature of a coolant fluid at an inlet of an internal combustion engine.
A vehicle, such as a car, a motorcycle, or any other type of automobile may be equipped with an internal combustion engine to provide a source of power for the vehicle. Power from the engine can include mechanical power (to enable the vehicle to move) and electrical power (to enable electronic systems, pumps, etc. within the vehicle to operate). As an internal combustion engine operates, the engine and its associated components generate heat, which can damage the engine and its associated components if left unchecked.
To reduce heat in the engine, a coolant system circulates a coolant fluid through cooling passages within the engine. The coolant fluid absorbs heat from the engine and is then cooled via a heat exchange in a radiator when the coolant fluid is pumped out of the engine and into the radiator. Accordingly, the coolant fluid becomes cooler and is then circulated back through the engine to cool the engine and its associated components.

SUMMARY

In one exemplary embodiment, a computer-implemented method for controlling temperature of a coolant fluid at an inlet of an internal combustion engine includes receiving, by a processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine. The method further includes receiving, by a processing device, engine speed data indicating an engine speed of the internal combustion engine. The method further includes calculating, by the processing device, a radiator flow rate to achieve a temperature set-point at an inlet of the engine based at least in part on the total fuel burned data and the engine speed data. The method further includes adjusting, by the processing device, a radiator flow based at least in part on the radiator flow rate.
In some embodiments, adjusting the radiator flow further comprises increasing flow of the coolant fluid to a radiator and decreasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow further comprises decreasing flow of the coolant fluid to a radiator and increasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow of the coolant fluid further comprises controlling a valve to adjust the radiator flow of the coolant fluid. In some embodiments, calculating the radiator flow rate to achieve a temperature set-point at an inlet of the engine is further based at least in part on a radiator temperature. In some embodiments, calculating the radiator flow rate is further based at least in part on an engine outlet temperature. In some embodiments, calculating the radiator flow rate is further based at least in part on an ambient pressure.
In another exemplary embodiment, a system for controlling temperature of a coolant fluid at an inlet of an internal combustion engine includes a memory including computer readable instructions and a processing device for executing the computer readable instructions for performing a method. In examples, the method includes receiving, by a processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine. The method further includes receiving, by a processing device, engine speed data indicating an engine speed of the internal combustion engine. The method further includes calculating, by the processing device, a radiator flow rate to achieve a temperature set-point at an inlet of the engine based at least in part on the total fuel burned data and the engine speed data. The method further includes adjusting, by the processing device, a radiator flow based at least in part on the radiator flow rate.
In some embodiments, adjusting the radiator flow further comprises increasing flow of the coolant fluid to a radiator and decreasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow further comprises decreasing flow of the coolant fluid to a radiator and increasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow of the coolant fluid further comprises controlling a valve to adjust the radiator flow of the coolant fluid. In some embodiments, calculating the radiator flow rate is further based at least in part on a radiator temperature. In some embodiments, calculating the radiator flow rate is further based at least in part on an engine outlet temperature. In some embodiments, calculating the radiator flow rate is further based at least in part on an ambient pressure.
In yet another exemplary embodiment a computer program product for controlling temperature of a coolant fluid at an inlet of an internal combustion engine includes a computer readable storage medium having program instructions embodied therewith, wherein the computer readable storage medium is not a transitory signal per se, the program instructions executable by a processing device to cause the processing device to perform a method. In examples, the method includes receiving, by a processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine. The method further includes receiving, by a processing device, engine speed data indicating an engine speed of the internal combustion engine. The method further includes calculating, by the processing device, a radiator flow rate to achieve a temperature set-point at an inlet of the engine based at least in part on the total fuel burned data and the engine speed data. The method further includes adjusting, by the processing device, a radiator flow based at least in part on the radiator flow rate.
In some embodiments, adjusting the radiator flow further comprises increasing flow of the coolant fluid to a radiator and decreasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow further comprises decreasing flow of the coolant fluid to a radiator and increasing flow of the coolant fluid through a radiator bypass. In some embodiments, adjusting the radiator flow of the coolant fluid further comprises controlling a valve to adjust the radiator flow of the coolant fluid. In some embodiments, calculating the radiator flow rate is further based at least in part on a radiator temperature, an engine outlet temperature, and an ambient pressure.
The above features and advantages, and other features and advantages, of the disclosure are readily apparent from the following detailed description when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages, and details appear, by way of example only, in the following detailed description, the detailed description referring to the drawings in which:

FIG. 1 depicts a vehicle engine including an inlet temperature controller for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments of the present disclosure;

FIGS. 2A, 2B, and 2C depict graphs of coolant boiling characteristics, according to embodiments of the present disclosure;

FIG. 3 depicts a flow diagram of a method for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments of the present disclosure;

FIG. 4 depicts a flow diagram of a method for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments of the present disclosure; and

FIG. 5 depicts a block diagram of a processing system for implementing the techniques described herein, according to embodiments of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term module refers to processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality.
The technical solutions described herein provide for controlling temperature of a coolant fluid at an inlet of an internal combustion engine. Modern engines have become more efficient at combusting fuel, which causes an increase in the operating temperature of the engine. By controlling temperature of the coolant fluid, it is possible to operate the engine at the highest temperature possible without comprising the hardware integrity of the engine. This increases engine and fuel efficiency while preventing failure of the engine.
The present techniques regulate coolant fluid flow through the radiator based on measured coolant fluid temperature at the inlet of the engine. The temperature control is based primarily on management of the flow of coolant fluid through the radiator as a function of the inlet temperature set-point. The target temperate at the inlet of the engine is variable depending on the engine operating point, which is a function of total fuel burned and engine speed. An inlet temperature controller calculates a radiator flow rate (i.e., a rate of coolant flow from the radiator) to achieve a temperature set-point at the inlet of the engine in order to compensate for the thermal power introduced in the combustion chamber of the engine. The inlet temperature controller calculates the radiator flow based on total fuel burned and engine speed. The inlet temperature controller can also compensate for radiator temperature, engine outlet temperature, and ambient pressure, among others.
FIG. 1 depicts a vehicle engine 100 including an inlet temperature controller 102 for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments of the present disclosure. The vehicle engine 100 includes at least a main coolant pump (“pump”) 104 an engine block 110, an engine head 112, other engine components 114 (e.g., a turbo charger, an exhaust gas re-circulator, etc.), a main rotary value 130, an engine oil heater 116, a transmission oil heater 118, and a radiator 120. The main rotary valve 130 includes a first valve 140 having a first inlet 141, a second inlet 142, and an outlet 143. The main rotary valve 130 also includes a second valve 150 having an inlet 151, a first outlet 152, and a second outlet 153. The various components of the vehicle engine 100 are connected and arranged as shown in FIG. 1 according to embodiments, and the solid lines among the components represent the fluid connections among the components, with arrows representing the flow direction of the fluid.
The main rotary valve 130, including the first valve 140 and the second valve 150, are controlled by the inlet temperature controller 102. In particular, the inlet temperature controller 102 can cause the first valve 140 to direct flow from either the first inlet 141 and/or the second inlet 142 into the engine oil heater 116 and the transmission oil heater 118 through the outlet 143. Similarly, the inlet temperature controller 102 can cause the second valve 150 to direct flow from the engine block 110 and the engine head 112 into the radiator 120 and/or the radiator bypass 122 through the first outlet 152 and the second outlet 153.
Coolant fluid is cooled by the radiator 120 and is pumped out of the radiator 120 by the pump 104 back into the engine block 110, the engine head 112, and the other components 114 (collectively, the “inlet” of the engine). Managing the flow out of the radiator 120 enables mixing cold coolant with hot coolant in order to provide the coolant to the vehicle engine 100 at a desired temperature.
The inlet temperature controller 102 controls temperature of coolant fluid at the inlet of an internal combustion engine. To control the temperature at the inlet of the engine, the inlet temperature controller 102 calculates a radiator flow rate (i.e., a rate of coolant flow from the radiator) to meet the inlet temperature set-point based on total fuel burned and engine speed. This provides compensation for the thermal power introduced in the combustion chamber of the vehicle engine 100. The inlet temperature controller can also compensate for radiator temperature, engine outlet temperature, and ambient pressure, among others.
Radiator flow rate is a function of the engine speed and total fuel burned in order to achieve optimal combustion efficiency of the vehicle engine 100 without overcoming the limits of the components of the vehicle engine 100. Radiator flow rate increases as the engine speed and total fuel burned increases, for example. The radiator flow rate is calculated to maintain a temperature set-point for the vehicle engine 100.
The temperature set-point during a low power operating condition of the vehicle engine 100 is very close to the hardware limits of the vehicle engine 100. This is a particular characteristic of diesel engines because the diesel engines can operate at very high temperatures. However, the temperature set-point during high power operating conditions is lower than at low power operating conditions. That is, the temperature set-point during high power operating conditions, when heat must be removed from the vehicle engine 100 in order to avoid the hardware limits of the vehicle engine 100, is reduced from the temperature set-point at lower power operating condition. This can be observed in FIG. 2A, which depicts a graph 200A of coolant boiling characteristics, according to embodiments. In particular, the graph 200A illustrates that 110 degrees C. is acceptable in a low power operation but that temperature can rise above the hardware limit in high power operation. The graph 200A plots coolant pressure in kPa versus coolant saturation temperature in degrees C. During low power operation, the radiator flow rate is lower than during high power operation.
With continuing reference to FIG. 1, the inlet temperature controller 102 can also account for radiator temperature information, engine outlet temperature information, and ambient pressure information. For example, the inlet temperature controller 102 can compensate for the cooling capacity of the radiator 120 by observing the radiator temperature. This compensation acts directly on the inlet temperature controller 102 calibration considering the cooling capacity of the radiator 120. For example, the lower the coolant fluid temperature is in the radiator 120, the slower the inlet temperature controller 102 can react to cooling requests.
The inlet temperature controller 102 can also compensate for variations caused by aged components (e.g., an injector, a valve, etc.). Since the vehicle engine 100 operates close to a critical temperature (i.e., the temperature at which a component may fail), a drifted or aged component (e.g., an injector, a valve, etc.) can produce an unexpected change in temperature with respect to its calibration in normal conditions. This can be observed in FIG. 2B, which depicts a graph 200B of coolant boiling characteristics, according to embodiments. In particular, the graph 200B illustrates that hardware limits can be reached as a result of an aging component. The graph 200B plots coolant pressure in kPa versus coolant saturation temperature in degrees C. This feature allows a reduction in the engineering margin that engineers must take into account when designing the vehicle engine 100 and its cooling system.
Additionally, with continuing reference to FIG. 1, the inlet temperature controller 102 can compensate for ambient pressure by observing ambient pressure data collected by an ambient pressure sensor (not shown). This enables the radiator flow rate to be adjusted based on pressure fluctuations caused by altitude. Also, in this case, the working temperatures of the vehicle engine 100 can be harmful to the engine to operate the vehicle at certain altitudes without compensating for the ambient pressure at altitude. This can be observed in FIG. 2C, which depicts a graph 200C of coolant boiling characteristics, according to embodiments. In particular, the graph 200C illustrates that in higher altitudes, the pressure of the coolant system is lower than at sea level and that compensation is therefore needed. The graph 200C plots coolant pressure in kPa versus coolant saturation temperature in degrees C. This feature allows a reduction in the engineering margin that engineers must take into account when designing the vehicle engine 100 and its cooling system.
With continuing reference to FIG. 1, in embodiments, the inlet temperature controller 102 can be a combination of hardware and programming. The programming may be processor executable instructions stored on a tangible memory, and the hardware can include a processing device for executing those instructions. Thus a system memory can store program instructions that when executed by the processing device implement the functionality described herein. Other engines/modules/controllers may also be utilized to include other features and functionality described in other examples herein. Alternatively or additionally, the inlet temperature controller 102 can be implemented as dedicated hardware, such as one or more integrated circuits, Application Specific Integrated Circuits (ASICs), Application Specific Special Processors (ASSPs), Field Programmable Gate Arrays (FPGAs), or any combination of the foregoing examples of dedicated hardware, for performing the techniques described herein.
FIG. 3 depicts a flow diagram of a method 300 for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments. The method 300 may be implemented, for example, by the inlet temperature controller of FIG. 1, by the processing system 500 of FIG. 5 (described below), or by another suitable processing system or device.
Data indicating the total fuel burned by the vehicle engine 100 and data indicating the engine speed of the vehicle operated by the vehicle engine 100 are received at block 302. At block 304, a coolant inlet temperature set-point (i.e., a temperature value set as a desired temperature of the coolant fluid at the engine input) is calculated. At block 304, the coolant inlet temperature set-point is reduced according to ambient pressure. At block 306, the inlet temperature set-point is adjusted to compensate for errors in tracking, such as a result of a drifting component.
At block 308, a rate limiter is applied to the inlet temperature set-point to prevent a radiator flow rate from exceeding a limit. At block 310, the inlet temperature tracking error is calculated by using the actual inlet temperature set-point and the current coolant fluid temperature at the engine input. At block 312, the tracking error is used to calculate the radiator flow rate by a set of calibrated coefficients that determines the nominal dynamic of the controller, and at block 314, the radiator outlet temperature is received and applied to the coefficients of the controller to determine the radiator flow rate dynamic response compensated with actual radiator cooling capability.
The second valve 150 of the main rotary valve 130 is then adjusted to provide the calculated radiator flow rate. For example, the first outlet 152 and the second outlet 153 of the second valve 150 are opened/closed to achieve the determined radiator flow rate. As the radiator flow rate increases, the first outlet valve 153 is opened to increase flow through the radiator 120. Concurrently, the first outlet 152 can be closed to reduce flow through the radiator bypass 122. Similarly, as the radiator flow rate decreases, the first outlet valve 153 is closed to reduce flow through the radiator 120. Concurrently, the first outlet 152 can be opened to increase flow through the radiator bypass 122.
FIG. 4 depicts a flow diagram of a method 400 for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, according to embodiments. The method 400 may be implemented, for example, by the inlet temperature controller of FIG. 1, by the processing system 500 of FIG. 5 (described below), or by another suitable processing system or device.
At block 402, the inlet temperature controller 102 receives total fuel burned data indicating a total amount of fuel burned by the internal combustion engine. At block 404, the inlet temperature controller 102 receives engine speed data indicating an engine speed of the internal combustion engine.
At block 406, the inlet temperature controller 102 calculates a radiator flow rate based at least in part on the total fuel burned data and the engine speed data. According to embodiments of the present disclosure, the inlet temperature controller 102 can also utilize additional data to calculate the radiator flow rate, such as a radiator temperature, an engine outlet temperature, and an ambient pressure.
At block 408, the inlet temperature controller 102 adjusts a radiator flow of the coolant fluid based at least in part on the radiator flow rate. According to one or more embodiments, adjusting the radiator flow includes increasing flow of the coolant fluid to a radiator and decreasing flow of the coolant fluid through a radiator bypass. Conversely, in one or more embodiments, adjusting the radiator flow includes decreasing flow of the coolant fluid to a radiator and increasing flow of the coolant fluid through a radiator bypass.
Additional processes also may be included, and it should be understood that the processes depicted in FIG. 4 represent illustrations and that other processes may be added or existing processes may be removed, modified, or rearranged without departing from the scope and spirit of the present disclosure.
It is understood that the present disclosure is capable of being implemented in conjunction with any other type of computing environment now known or later developed. For example, FIG. 5 illustrates a block diagram of a processing system 500 for implementing the techniques described herein. In examples, processing system 500 has one or more central processing units (processors) 21 a, 21 b, 21 c, etc. (collectively or generically referred to as processor(s) 21 and/or as processing device(s)). In aspects of the present disclosure, each processor 21 may include a reduced instruction set computer (RISC) microprocessor. Processors 21 are coupled to system memory (e.g., random access memory (RAM) 24) and various other components via a system bus 33. Read only memory (ROM) 22 is coupled to system bus 33 and may include a basic input/outlet system (BIOS), which controls certain basic functions of processing system 500.
Further illustrated are an input/outlet (I/O) adapter 27 and a network adapter 26 coupled to system bus 33. I/O adapter 27 may be a small computer system interface (SCSI) adapter that communicates with a hard disk 23 and/or another storage drive 25 or any other similar component. I/O adapter 27, hard disk 23, and storage device 25 are collectively referred to herein as mass storage 34. Operating system 40 for execution on processing system 500 may be stored in mass storage 34. A network adapter 26 interconnects system bus 33 with an outside network 36 enabling processing system 500 to communicate with other such systems.
A display (e.g., a display monitor) 35 is connected to system bus 33 by display adapter 32, which may include a graphics adapter to improve the performance of graphics intensive applications and a video controller. In one aspect of the present disclosure, adapters 26, 27, and/or 32 may be connected to one or more I/O busses that are connected to system bus 33 via an intermediate bus bridge (not shown). Suitable I/O buses for connecting peripheral devices such as hard disk controllers, network adapters, and graphics adapters typically include common protocols, such as the Peripheral Component Interconnect (PCI). Additional input/outlet devices are shown as connected to system bus 33 via user interface adapter 28 and display adapter 32. A keyboard 29, mouse 30, and speaker 31 may be interconnected to system bus 33 via user interface adapter 28, which may include, for example, a Super I/O chip integrating multiple device adapters into a single integrated circuit.
In some aspects of the present disclosure, processing system 500 includes a graphics processing unit 37. Graphics processing unit 37 is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for outlet to a display. In general, graphics processing unit 37 is very efficient at manipulating computer graphics and image processing, and has a highly parallel structure that makes it more effective than general-purpose CPUs for algorithms where processing of large blocks of data is done in parallel.
Thus, as configured herein, processing system 500 includes processing capability in the form of processors 21, storage capability including system memory (e.g., RAM 24), and mass storage 34, input means such as keyboard 29 and mouse 30, and outlet capability including speaker 31 and display 35. In some aspects of the present disclosure, a portion of system memory (e.g., RAM 24) and mass storage 34 collectively store an operating system to coordinate the functions of the various components shown in processing system 500.
The descriptions of the various examples of the present disclosure have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described techniques. The terminology used herein was chosen to best explain the principles of the present techniques, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the techniques disclosed herein.
While the above disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from its scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the present techniques not be limited to the particular embodiments disclosed, but will include all embodiments falling within the scope of the application.

Claims

1. A computer-implemented method for controlling a temperature of a coolant fluid at an inlet of an internal combustion engine, the method comprising:

receiving, by a processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine;

receiving, by the processing device, engine speed data indicating an engine speed of the internal combustion engine; and

calculating, by the processing device, a radiator flow rate to achieve a temperature set point at an inlet of the engine based at least in part on the total fuel burned data and the engine speed data; and

adjusting, by the processing device, a radiator flow based at least in part on the radiator flow rate, wherein adjusting the radiator flow of the coolant fluid further comprises controlling a valve to adjust the radiator flow of the coolant fluid, the valve comprising an inlet connected to an outlet of an engine block and an outlet of an engine head, a first outlet connected to a radiator bypass, and a second outlet connected to a radiator.

2. The computer-implemented method of claim 1, wherein

adjusting the radiator flow further comprises increasing flow of the coolant fluid to the radiator and decreasing flow of the coolant fluid through the radiator bypass.

3. The computer-implemented method of claim 1, wherein adjusting the radiator flow further comprises decreasing flow of the coolant fluid to the radiator and increasing flow of the coolant fluid through the radiator bypass.

4. (canceled)

5. The computer-implemented method of claim 1, wherein calculating the radiator flow rate is further based at least in part on a radiator temperature.

6. The computer-implemented method of claim 1, wherein calculating the radiator flow rate is further based at least in part on an engine outlet temperature.

7. The computer-implemented method of claim 1, wherein calculating the radiator flow rate is further based at least in part on an ambient pressure.

8. A system for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, the system comprising:

a memory comprising computer readable instructions; and

a processing device for executing the computer readable instructions for performing a method, the method comprising:

receiving, by the processing device, total fuel burned data indicating a total amount of fuel burned by the internal combustion engine;

9. The system of claim 8, wherein adjusting the radiator flow further comprises increasing flow of the coolant fluid to the radiator and decreasing flow of the coolant fluid through the radiator bypass.

10. The system of claim 8, wherein adjusting the radiator flow further comprises decreasing flow of the coolant fluid to the radiator and increasing flow of the coolant fluid through the radiator bypass.

11. (canceled)

12. The system of claim 8, wherein calculating the radiator flow rate is further based at least in part on a radiator temperature.

13. The system of claim 8, wherein calculating the radiator flow rate is further based at least in part on an engine outlet temperature.

14. The system of claim 8, wherein calculating the radiator flow rate is further based at least in part on an ambient pressure.

15. A computer program product for controlling temperature of a coolant fluid at an inlet of an internal combustion engine, the computer program product comprising:

a computer readable storage medium having program instructions embodied therewith, wherein the computer readable storage medium is not a transitory signal per se, the program instructions executable by a processing device to cause the processing device to perform a method comprising:

16. The computer program product of claim 15, wherein adjusting the radiator flow further comprises increasing flow of the coolant fluid to the radiator and decreasing flow of the coolant fluid through the radiator bypass.

17. The computer program product of claim 15, wherein adjusting the radiator flow further comprises decreasing flow of the coolant fluid to the radiator and increasing flow of the coolant fluid through the radiator bypass.

18. (canceled)

19. The computer program product of claim 15, wherein calculating the radiator flow rate is further based at least in part on a radiator temperature, an engine outlet temperature, and an ambient pressure.