Combustion engines employ exhaust gas recirculation (EGR) to reduce NOx emissions, which are generated in larger quantities at higher peak engine combustion temperatures. Recirculating exhaust gas to the engine intake lowers peak engine combustion temperatures by diluting the oxygen concentrations, which lowers combustion rates, and also by providing additional heat capacity for absorbing heat generated from engine combustion. However, higher in-cylinder peak temperatures and higher NOx emissions can be generated in an engine when the EGR distribution among each of an engine's cylinders is non-uniform. Typical EGR distribution measurement systems measure intake gas from a single cylinder intake with a gas analyzer for determining the EGR distribution in that cylinder. In order to characterize the EGR distribution among all individual engine cylinders, the single-cylinder measurement is for each individual engine cylinder and engine operating condition, with each cylinder being sampled over a range of engine operating conditions, including EGR valve set points for each engine running state.
The inventors herein have recognized potential issues with such systems. First, because conventional measurement of cylinder EGR distribution is performed on an individual cylinder-by-cylinder basis, the testing process can be lengthy, even when considering a lone engine running state set point. Furthermore, because a conventional gas analyzer instrument is used, intake gas must flow from the engine to the gas analysis chamber within the gas analyzer positioned external to and at a distance from the engine. Typically, the sample gas must flow through a tortuous path within the gas analyzer instrument before reaching the sample chamber within. As such, delays in gas transport from the engine to the gas analyzer and delays in analysis time can be significant and can severely lower the speed and efficiency of the measurement system. As such, development and validation of EGR systems can be laborious and costly, sometimes involving months of active testing and measurement with extensive equipment auxiliary to the engine.
In one example, the issues described above may be at least partially addressed by a method comprising fluidly coupling an intake runner of an engine to a vacuum pump, diverting a portion of intake charge gas from the intake runner to a gas composition sensor with the vacuum pump, measuring an oxygen concentration of the diverted intake charge portion with the gas composition sensor, and estimating an EGR concentration of the intake charge based on the measured oxygen concentration. In this way, the vacuum pump actively draws the intake charge gas to the gas composition sensor, thereby reducing transport delays for sampling gas from the cylinder intake runners to the gas composition sensors. As one example, the method may further comprise fluidly coupling a plurality of intake runners of the engine to the vacuum pump, each of the intake runners fluidly coupled to a separate engine combustion cylinder. In this way, the vacuum pump may sample from a plurality of cylinder intake runners, thereby reducing a testing time for development and validation of an EGR system.
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.