Internal combustion engines may include water injection systems that inject water from a storage tank into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold, ports, etc.) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions.
As explained above, water may be injected into different locations, including the intake manifold, intake ports of engine cylinders, or directly into engine cylinders. The inventors have recognized that water injection at different locations may provide different benefits depending on engine operating conditions. For example, manifold injection, direct injection, and port injection toward the manifold may provide increased cooling of the charge air, thereby reducing knock tendency. Additionally, port injection onto the intake valves may increase a dilution effect of the injected water over manifold injection, thereby reducing engine pumping losses. However, an actual amount of water injected at an engine may be different than a commanded amount. For example, water injection errors may arise due to water injector fouling or wear, due to incomplete vaporization of the injected water, which may result from impurities in the water being injected, variation of the injected water pH level from an expected level, a CAC outlet temperature being different than expected, etc. As a result, a desired water injection benefit may not be provided to the engine.
In one example, the issues described above may be addressed by a method for an engine comprising, responsive to water injection into an intake manifold via a port water injector, adjusting engine operation based on a change in exhaust dilution; and responsive to water injection into the intake manifold via a manifold water injector, adjusting engine operation based on a change in intake dilution. In this way, water injection errors may be diagnosed differently based on the location of the water injection as well as based on the intended benefit of the water injection.
As an example, an engine may be configured with multiple water injectors such as a manifold water injector, a port water injector, and a direct water injector. An engine controller may determine a total amount of water to inject and a location to inject the water based on engine operating conditions. For example, at low-mid engine loads, engine combustion stability may be improved by increasing the charge dilution via injection of water into the intake manifold. Additionally, a portion of the total water to be injected may be port injected onto a hot surface of a closed intake valve to meet the dilution demand. Since charge dilution via water injection affects the amount of water in the engine, the actual amount of water injected may be detected via an oxygen sensor. Specifically, a change in the output of an intake oxygen sensor may be used to infer the actual amount of water injected into the intake manifold, while a change in the output of an exhaust oxygen sensor may be used to infer the actual amount of water injected into the intake port. By comparing the actual water injection amount to the commanded amount, the controller may learn a water injection error and compensate accordingly. For example, during a subsequent water injection, a duty cycle of the manifold and/or port injector may be adjusted to compensate for the error. As another example, EGR flow to the engine may be adjusted to compensate for any dilution deficit. In comparison, during mid to high engine load conditions, knock control may be provided by using manifold water injection to provide charge cooling. During such conditions, the water injection error may be learned as a function of a change in the manifold temperature (via a manifold temperature sensor), and compensated for via adjustments to the duty cycle of the manifold injector, via direct injection of water into a cylinder, and/or spark timing adjustments.
In this way, by selecting a water injection sensing mode based on the engine load and the selected water injector(s), water injection errors may be more accurately measured and compensated for. The technical effect of using a different set of sensors to measure water injection used for charge dilution (at low-mid engine loads) versus water injection used for charge cooling (at mid-high engine loads), water injection may be better controlled. By providing a desired dilution to the engine, pumping losses may be decreased and combustion stability may be improved. By providing a desired charge cooling to the engine, knock related issues may be reduced. Overall, water injection benefits may be extended over a wider range of engine operation, improving engine performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.