Turbocharged and supercharged engines may be configured to compress ambient air entering the engine in order to increase power. Compression of the air may cause an increase in air temperature, thus, a charge air cooler may be utilized to cool the heated air thereby increasing its density and further increasing the potential power of the engine. Ambient air from outside the vehicle travels across the CAC to cool intake air passing through the inside of the CAC. Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the CAC, or in the internal passages, and cooling turbulators. When torque is increased, such as during acceleration, increased mass air flow may strip the condensate from the CAC, drawing it into the engine and increasing the likelihood of engine misfire.
Example approaches of addressing combustion issues (e.g., misfire) resulting from condensate ingestion involve avoiding condensate build-up. However, the inventors herein have recognized potential issues with such methods. Specifically, while some methods may reduce or slow condensate formation in the CAC, condensate may still build up over time. If this build-up cannot be stopped, ingestion of the condensate during acceleration may cause engine misfire. In addition, based on the engine speed-load condition, as well as the configuration of the engine (e.g., based on whether the engine is V-engine with distinct banks or an in-line engine), some cylinders may receive more condensate than others, rendering them more prone to combustion issues than others. Other example approaches of addressing the combustion issues involve trapping and/or draining the condensate from the CAC. While this may reduce condensate levels in the CAC, condensate is moved to an alternate location or reservoir, which may be subject to other condensate problems such as freezing and corrosion. Further, the reservoir may add component cost and complexity. Still other approaches purge condensate from the CAC opportunistically when engine airflow increases, such as during a driver pedal tip-in. However, the tip-in may not occur at the same time that condensate purging is required. In the interim, condensate may continue to be ingested in the engine, degrading combustion.
In one example, the above described issues may be at least partly addressed by a method for purging condensate from the CAC during vehicle operating conditions. The method may comprise: in response to condensate level in a charge air cooler, adjusting fuel injection timing while increasing engine airflow to a level greater than requested by a vehicle operator. In this way, one or more engine cylinders may be temporarily operated in a lean stratified mode to purge the condensate while the operation of other engine cylinders is adjusted to maintain a stoichiometric exhaust air-fuel ratio.
In one example, an engine system may include a charge air cooler coupled downstream of a compressor and upstream of an intake throttle. During engine operation, condensate may collect at the charge air cooler. In response to condensate levels being higher than a threshold, purging conditions may be considered met and a clean-out cycle may be initiated to remove the condensate. In particular, the fuel injection timing of one or more engine cylinders may be shifted from an injection timing that provides a homogeneous cylinder air-fuel charge that is ignited with spark to an alternate injection timing that provides at least some stratified cylinder air-fuel charge that is ignited with spark. By operating at least some cylinders in a lean stratified mode, an engine airflow level can be increased to or above a blow-off level where condensate is blown into the engine.
As an example, cylinders that are less sensitive to water ingestion (that is, cylinders less prone to ingestion induced misfires) may be operated in the lean stratified mode while the remaining cylinders (that is, cylinders more prone to ingestion induced misfires) are operated rich such that an overall exhaust air-fuel ratio is maintained at or around stoichiometry. The degree of leanness may be adjusted based on the amount of condensate at the cylinder so that the engine airflow can be sufficiently increased. The water ingestion sensitivity of the cylinders may be determined based on engine speed-load conditions at the time of the purging, an amount of condensate received in each cylinder, a configuration of the engine, cylinder firing order, etc. Adjusting the fuel injection timing of a cylinder to transition from the homogenous mode of cylinder combustion to the lean stratified mode of cylinder combustion may include shifting fuel injection timing from an intake stroke to a compression stroke, increasing a number of injections per combustion event, adjusting a split ratio of fuel delivery split between the injections, etc.
In this way, condensate may be periodically cleaned from a charge air cooler by operating one or more cylinders in a lean stratified mode. By adjusting the fuel injection timing of a cylinder such that an airflow level is increased to a level that enables blowing off of condensate from the CAC, purging can be performed without waiting for a tip-in event. At the same time, by adjusting the fuel injection timing to providing a stratified fuel injection, a rich environment can be maintained in the vicinity of the cylinder's spark plug, allowing for a more stable combustion. By adjusting the fuel injection timing so that an overall exhaust air-fuel ratio is maintained at stoichiometry, engine performance during the purging is improved.
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.