Exhaust catalyst light-off in an opposed-piston engine
In an opposed-piston engine which includes a catalytic aftertreatment device in its exhaust system an exhaust gas condition indicating a catalyst temperature of the aftertreatment device is monitored. When the catalyst temperature is near or below a light-off temperature, a catalyst light-off procedure is executed to elevate the temperature of the catalyst.
1. A method of operating an opposed-piston engine comprising a cylinder, an intake port near a first end of the cylinder, an exhaust port near a second end of the cylinder, a charge air passage configured to transport a mass airflow to the intake port, an exhaust passage configured to transport exhaust gas from the exhaust port, a backpressure valve in the exhaust passage, and a catalytic aftertreatment device in the exhaust passage, the catalytic aftertreatment device including a catalyst having a light-off temperature, the method comprising:
initiating operation of the opposed-piston engine;
operating the opposed-piston engine by compression ignition of injected fuel in a combustion chamber formed between end surfaces of a pair of pistons disposed for opposing movement in the cylinder;
sensing an exhaust gas condition indicative of a temperature of the catalyst while the opposed-piston engine is operating;
initiating a catalyst light-off procedure in response to the exhaust gas condition according to an operating state of the opposed-piston engine;
conducting the catalyst light-off procedure when the opposed-piston engine is idling by increasing the mass airflow to the intake port and closing the backpressure valve;
conducting the catalyst light-off procedure when the opposed-piston engine is in a tip-in transient condition by increasing the mass airflow to the intake port, increasing an amount of the injected fuel, and advancing an injection timing of the injected fuel;
conducting the catalyst light-off procedure when the opposed-piston engine is in a tip-out transient condition by decreasing the mass airflow to the intake port and retarding the injection timing of the injected fuel; and,
transitioning the opposed-piston engine to a normal operating condition when the exhaust gas condition indicates that the temperature of the catalyst exceeds a catalyst light-off threshold during the catalyst light-off procedure.
2. The method of claim 1 , wherein the exhaust gas condition is an exhaust gas temperature.
3. The method of claim 2 , wherein increasing the mass airflow to the intake port comprises regulating a turbocharger and a supercharger of the opposed-piston engine.
4. The method of claim 3 , wherein regulating the turbocharger comprises closing a wastegate in the exhaust passage.
5. The method of claim 3 , wherein regulating the turbocharger comprises closing an adjustable element of a turbine of the turbocharger.
6. The method of claim 3 , wherein regulating the supercharger comprises increasing a speed of the supercharger.
7. The method of claim 6 , wherein increasing the speed of the supercharger comprises changing a speed ratio of a supercharger drive device.
8. The method of claim 1 , wherein the exhaust gas condition is an exhaust gas enthalpy.
9. The method of claim 8 , wherein increasing the mass airflow to the intake port comprises regulating a turbocharger and a supercharger of the opposed-piston engine.
10. The method of claim 9 , wherein regulating the turbocharger comprises closing a wastegate in the exhaust passage.
11. The method of claim 9 , wherein regulating the turbocharger comprises closing an adjustable element of a turbine of the turbocharger.
12. The method of claim 9 , wherein regulating the supercharger comprises increasing a speed of the supercharger.
13. The method of claim 12 , wherein increasing the speed of the supercharger comprises changing a speed ratio of a supercharger drive device.
14. An opposed-piston engine, comprising:
a cylinder with an intake port near a first end of the cylinder and an exhaust port near a second end of the cylinder;
a pair of pistons disposed for opposing movement in the cylinder;
a charge air passage configured to transport a mass airflow to the intake port;
an exhaust passage configured to transport exhaust gas from the exhaust port;
a backpressure valve in the exhaust passage; and
a catalytic aftertreatment device in the exhaust passage, the catalytic aftertreatment device including a catalyst having a light-off temperature,
the opposed-piston engine further comprising a control unit programmed to:
initiate operation of the opposed-piston engine;
sense an exhaust gas condition indicative of a temperature of the catalyst while the opposed-piston engine is operating by compression ignition of fuel injected into a combustion chamber formed between end surfaces of the pair of pistons;
initiate a catalyst light-off procedure in response to the exhaust gas condition, according to an operating state of the opposed-piston engine;
conduct the catalyst light-off procedure when the opposed-piston engine is in an idling operating state by increasing the mass airflow to the intake port and closing the backpressure valve;
conduct the catalyst light-off procedure when the opposed-piston engine is in a tip-in transient condition by increasing the mass airflow to the intake port, increasing an amount of the injected fuel, and advancing an injection timing of the injected fuel;
conduct the catalyst light-off procedure when the opposed-piston engine is in a tip-out transient condition by decreasing the mass airflow to the intake port and retarding the injection timing of the injected fuel; and,
transition the opposed-piston engine to a normal operating condition when the exhaust gas condition indicates that the temperature of the catalyst exceeds a catalyst light-off threshold during the catalyst light-off procedure.
15. The engine of claim 14 , wherein the exhaust gas condition is an exhaust gas temperature.
16. The engine of claim 15 , wherein increasing the mass airflow to the intake port comprises regulating a turbocharger and a supercharger of the opposed-piston engine.
17. The engine of claim 16 , wherein regulating the turbocharger comprises closing a wastegate in the exhaust passage.
18. The engine of claim 16 , wherein regulating the turbocharger comprises closing an adjustable element of a turbine of the turbocharger.
19. The engine of claim 16 , wherein regulating the supercharger comprises increasing a speed of the supercharger.
20. The engine of claim 19 , wherein increasing the speed of the supercharger comprises changing a speed ratio of a supercharger drive device.
21. The engine of claim 14 , wherein the exhaust gas condition is an exhaust gas enthalpy.
22. The engine of claim 21 , wherein increasing the mass airflow to the intake port comprises regulating a turbocharger and a supercharger of the opposed-piston engine.
23. The engine of claim 22 , wherein regulating the turbocharger comprises closing a wastegate in the exhaust passage.
24. The engine of claim 22 , wherein regulating the turbocharger comprises closing an adjustable element of a turbine of the turbocharger.
25. The engine of claim 22 , wherein regulating the supercharger comprises increasing a speed of the supercharger.
26. The engine of claim 25 , wherein increasing the speed of the supercharger comprises changing a speed ratio of a supercharger drive device.