Exhaust catalyst light-off in an opposed-piston engine
AssigneeAchates Power, Inc.
InventorsAhmad GHAZI, Daniel M. SCHUM, Fabien G. REDON, Samrat M. PATIL
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Abstract
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.
Claims38
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.
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;
- 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.
A catalyst light-off apparatus for an opposed-piston engine, comprising:
- an exhaust passage configured to receive a flow of exhaust gas produced by combustion of a mixture of air and fuel in a cylinder of the opposed-piston engine;
- a catalyst apparatus disposed in the exhaust passage, in series with a turbine of a turbocharger;
- an exhaust gas sensor arrangement configured to detect an exhaust gas condition of the exhaust gas that indicates a catalyst temperature of the catalyst apparatus;
- an engine control unit electrically connected to the exhaust gas sensor arrangement and programmed to:
- perform a cold start procedure to initiate a fuel-injected, compression-ignition mode of operation by cranking the opposed piston engine;
- determine whether a stable combustion is achieved during the cold start procedure;
- when the stable combustion is achieved, determine whether the exhaust gas condition indicates that a temperature of the catalyst is below a light-off temperature of the catalyst;
- and,
- when the temperature of the catalyst is below the light-off temperature of the catalyst, increase a flow of pressurized charge air into an intake port of the cylinder and restrict the flow of exhaust gas in the exhaust passage until the exhaust gas condition indicates that the temperature of the catalyst exceeds the light-off temperature.
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 supercharger configured to pump air to the intake port, an exhaust passage configured to transport exhaust from the exhaust port, a turbocharger comprising a turbine in the exhaust passage and a compressor on an upstream side of the supercharger, a backpressure valve in the exhaust passage on a downstream side of the turbine, and a catalytic aftertreatment device in the exhaust passage, the catalytic aftertreatment device comprising a catalyst having a light-off temperature, the method comprising:
- initiating compression-ignited combustion in the cylinder by cranking the opposed-piston engine;
- when cranking ceases as compression-ignited combustion continues, elevating a catalyst temperature of the catalytic aftertreatment device by:
- regulating the turbine and the supercharger to increase mass airflow into the intake port;
- and,
- closing the backpressure valve;
- determining an exhaust gas condition indicative of the catalyst temperature;
- as an indicated catalyst temperature approaches the light-off temperature, transitioning the engine to a normal operating condition.
Dependencies are inferred from the claim text.