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The use of EGR for NOX reduction is today a standard technology for diesel engines. The mixing of air and EGR is an important issue, especially for high-pressure EGR-systems. An uneven distribution of EGR between the cylinders can lead to higher overall engine emissions when some cylinders produce more soot, others more NOX than they would with a perfectly even distribution. It is therefore important to understand the processes that control the mixing between air and EGR. The mixing is influenced by both the geometry of the mixing area and the pulsating nature of the flow. The aim of this work is to point out the high importance of the pulses present in the EGR-flow. By simulation in 1-D and 3-D as well as by a fast measurement method, it is shown that the EGR is transported in the air flow in packets. This implies that the timing between intake valve opening and the positioning of the EGR packets has a high influence of the distribution of EGR between the cylinders.

The distribution of EGR between the cylinders of an internal combustion engine has been shown to have large impact on the engine emissions. Especially at high EGR, the combustion reacts sensibly to variations in the EGR-rate. A cylinder that receives excessive EGR produces soot emissions while a cylinder with too little EGR has increased NOX-formation. It is therefore important to have knowledge about the mixing of air and EGR in an engine. This study compares two different EGR-mixing measurement methods. The first is based on CO2 measurement with standard probes, placed at 36 different locations in the intake manifold of the engine. The second method uses a laser beam and a detector to gain information about the mixing with a high time-resolution. Additionally, 1-D simulations are used to gain information about the mixing process. To vary the mixing process on the engine, two different air/EGR mixers are used and their mixing performance is evaluated.