Engines may utilize a turbocharger or supercharger to compress ambient air entering the engine in order to increase power. Further, engines may recirculate a portion of exhaust gas from an exhaust passage to an intake passage, upstream of a compressor of the turbocharger. The recirculation of the exhaust gas may be referred to as low pressure exhaust gas recirculation (LP EGR). LP EGR may result in water condensation before the compressor due to the high water vapor content of the exhaust gas. When a temperature of the pre-compressor duct wall and/or a temperature of the EGR and intake air mixture fall below a dew point temperature, condensate may form in the pre-compressor duct of the compressor. Condensation at the pre-compressor duct wall may increase a risk of compressor wheel damage due to water droplet impingement. This may, in turn, lead to degraded noise, vibration, and harshness (NVH), degraded compressor performance, and damage to the engine due to compressor wheel erosion.
Other attempts to address compressor wheel damage from condensate include separating condensate from the LP EGR flow to avoid water droplets on the compressor wheel. One example approach is shown by Joergl et al. in U.S. Pat. No. 8,056,338. Therein, a dispersion apparatus is used to separate condensate from the EGR flow stream and then re-introduce the condensate at the axis of the compressor wheel to reduce corrosion of the compressor wheel.
However, the inventors herein have recognized potential issues with such systems. As one example, re-introducing condensate at the axis of the compressor wheel may still result in corrosion of the compressor wheel. Specifically, while separating condensate from the EGR flow may reduce condensate formation on the compressor wheel, not all condensate may be removed by this method. Further, condensate may still form before the compressor when ambient temperatures decrease and/or humidity increases, thereby causing the air temperature entering the compressor to decrease below the dew point temperature and condensate to form.
In one example, the issues described above may be addressed by a method for adjusting heating to a pre-compressor duct in response to condensate formation in the pre-compressor duct. Heating to the pre-compressor duct may be increased in response to a temperature of the pre-compressor duct wall decreasing below a dew point temperature. The temperature of the pre-compressor duct wall may be estimated based on one or more of a temperature of the intake air and recirculated air (e.g., air from exhaust gas recirculation) mixture in the pre-compressor duct, a temperature of gases in an exhaust gas recirculation system, an air flow rate, an exhaust gas recirculation flow rate, an ambient air temperature and vehicle speed. In one example, increasing heating to the pre-compressor duct may include activating an electric heating element embedded in the wall of the pre-compressor duct. In another example, increasing heating to the pre-compressor duct may include increasing a delivery rate of engine coolant to the pre-compressor duct wall. In some examples, heated engine coolant may first pass through an EGR valve integrated into the pre-compressor duct, thereby cooling the warmer EGR valve. The heated engine coolant may then pass through the pre-compressor duct wall, thereby increasing the temperature of the pre-compressor duct wall. In this way, the pre-compressor duct wall may be heated above the dew point temperature, thereby reducing condensate and subsequently, degradation of the compressor wheel.
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.