System and method of heat flow calculation in a physics-based piston temperature model
A system and method of providing real-time calculation of heat flow in an engine. A piston is disposed in a cylinder of an engine block and movable relative to the cylinder in response to combustion inside the cylinder. A temperature of the combustion inside the cylinder, an average temperature of the wall of the cylinder, and a surface area of the wall of the cylinder based on timing of combustion are determined. An estimated temperature of the piston is derived from calculating a heat fraction to the piston in real-time, via a controller, based on the determined temperature of the combustion, the determined average temperature of the wall of the cylinder, and the determined surface area of the wall of the cylinder. A state of the engine is controlled based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.
1. A method of providing real-time calculation of heat flow in an engine including an engine block having a cylinder and a wall that surrounds the cylinder, with a piston disposed in the cylinder and movable relative to the wall of the cylinder in response to timing of combustion in a combustion chamber inside the cylinder, and the piston is connected to a crankshaft via a connecting rod, the method comprising:
determining a temperature of the combustion inside the cylinder;
determining an average temperature of the wall of the cylinder taken only at an angular position of the crankshaft immediately after fifty percent of combustion heat is released to represent a steady-state heat transfer of a stationary theoretical engine at CA50;
determining a surface area of the wall of the cylinder based on the timing of the combustion;
calculating in real-time, via a controller, a heat fraction to the piston based on the determined temperature of the combustion, the determined average temperature of the wall of the cylinder, and the determined surface area of the wall of the cylinder; and
controlling a state of the engine based on an estimated temperature of the piston which is derived from the real-time calculation of the heat fraction to the piston.
2. The method as set forth in claim 1 :
further comprising determining a top surface area of the piston; and
wherein calculating in real-time the heat fraction to the piston is also based on the determined top surface area of the piston.
3. The method as set forth in claim 2 wherein calculating in real-time the heat fraction to the piston further includes continuously updating the estimated temperature of the piston at each next time step.
4. The method as set forth in claim 3 :
further comprising determining a total burned gas-heat convection rate; and
wherein calculating in real-time the heat fraction to the piston is also based on the determined total burned gas-heat convection rate.
5. The method as set forth in claim 1 wherein determining the surface area of the wall of the cylinder further comprises determining a displacement of the piston based on the angular position of the crankshaft after top-dead-center.
6. The method as set forth in claim 5 wherein determining the surface area of the wall of the cylinder further comprises determining a radius of the crankshaft and a length of the connecting rod.
7. The method as set forth in claim 6 wherein determining the surface area of the wall of the cylinder further comprises calculating in real-time, the displacement of the piston based on the angular position of the crankshaft after top-dead-center, the radius of the crankshaft, and the length of the connecting rod.
8. The method as set forth in claim 5 wherein determining the displacement of the piston based on the angular position of the crankshaft after top-dead-center is further defined as determining the surface area of the wall of the cylinder via displacement of the piston at the angular position of the crankshaft after fifty percent of combustion heat is released.
9. The method as set forth in claim 1 wherein controlling the state of the engine includes injecting fuel into the combustion chamber based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.
10. The method as set forth in claim 1 wherein controlling the state of the engine includes controlling an air-to-fuel ratio of the combustion chamber based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.
11. The method as set forth in claim 1 wherein controlling the state of the engine includes injecting oil into the cylinder around the piston based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.
12. The method as set forth in claim 1 wherein calculating in real-time the heat fraction to the piston further includes continuously updating the estimated temperature of the piston at each next time step.
13. The method as set forth in claim 1 :
further comprising determining a top surface area of the piston; and
further comprising calculating in real-time a rejection fraction based on the determined temperature of the combustion, the determined average temperature of the wall of the cylinder, the determined surface area of the wall of the cylinder, the determined top surface area of the piston, and the estimated temperature of the piston at each next time step.
14. The method as set forth in claim 13 :
further comprising determining a total burned gas-heat convection rate; and
wherein calculating in real-time the heat fraction to the piston is further defined as multiplying the rejection fraction with the total burned gas-heat convection rate.
15. The method as set forth in claim 1 wherein calculating in real-time, via the controller, the heat fraction to the piston further comprising calculating the real-time heat fraction to the piston using equation:
{dot over (Q)} PistonFraction ={dot over (Q)} totalrej (Rejection Fraction)
wherein:
{dot over (Q)} totalrej =the total burned gas heat convection rate;
{dot over (Q)} PistonFraction =the heat fraction to the piston;
Rejection Fraction=the heat fraction between piston and the wall of the cylinder calculated via equation:
Rejection
Fraction
=
A
p
(
T
comb
-
T
p
)
A
p
(
T
comb
-
T
p
)
+
A
w
(
T
comb
-
T
wall
)
wherein:
T p =the estimated temperature of the piston;
T comb the temperature of the combustion, back-calculated;
T wall =the average temperature of the wall of the cylinder;
A w =the surface area of the wall of the cylinder based on the timing of the combustion at the
angular position of the crankshaft after fifty percent of the combustion heat is released; and
A p =the top surface area of the piston.
16. An engine system for a movable platform; the system comprising:
an engine including an engine block having a cylinder and a wall that surrounds the cylinder;
a crankshaft supported via the engine block and rotatable relative to a longitudinal axis;
a piston connected to the crankshaft via a connecting rod, and the piston is disposed in the cylinder and movable relative to the wall of the cylinder in response to timing of combustion in a combustion chamber inside the cylinder; and
a controller configured to:
determine a temperature of the combustion inside the cylinder;
determine an average temperature of the wall of the cylinder ta ken only at a n angular position of the crankshaft immediately after fifty percent of combustion heat (CA50) is released to represent a steady-state heat transfer of a stationary theoretical engine at CA50;
determine a surface area of the wall of the cylinder based on the timing of the combustion;
calculate in real-time, via the controller, a heat fraction to the piston based on the determined temperature of the combustion, the determined average temperature of the wall of the cylinder, and the determined surface area of the wall of the cylinder; and
control a state of the engine based on an estimated temperature of the piston which is derived from the real-time calculation of the heat fraction to the piston.
17. The system as set forth in claim 16 wherein the controller is configured to:
determining a top surface area of the piston; and
calculate in real-time a rejection fraction based on the determined temperature of the combustion, the determined average temperature of the wall of the cylinder, the determined surface area of the wall of the cylinder, the determined top surface area of the piston, and the estimated temperature of the piston at each next time step.
18. The system as set forth in claim 17 wherein the controller is configured to determine a total burned gas-heat convection rate, and wherein the calculated real-time heat fraction to the piston further includes the controller being configured to multiply the rejection fraction with the total burned gas-heat convection rate.
19. The system as set forth in claim 16 wherein the controller is configured to control the state of the engine further includes the controller configured to signal a fuel injector to inject fuel into the combustion chamber based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.
20. The system as set forth in claim 16 wherein the controller is configured to control the state of the engine further includes the controller configured to control an air-to-fuel ratio of the combustion chamber based on the estimated temperature of the piston as derived from the real-time calculation of the heat fraction to the piston.