15. November 2016 | Engineering Service

FEV and Jaguar Land Rover focus on RDE

Investigations to extend the Low Pressure-EGR operating window

Low pressure exhaust gas recirculation (LP-EGR) enables a good tradeoff of engine-out NOx emissions vs. CO2. However, there is a risk of water condensation at the compressor inlet, depending on coolant and ambient air temperatures. Droplets of water can damage the compressor blades, thus limiting the usage of LP-EGR. An extension of the LP-EGR operating window—especially towards lower ambient temperature levels—would be highly beneficial in view of the latest legal requirements for real driving emissions (RDE). FEV and Jaguar Land Rover (JLR) have set up a climatic test bed in a joint research project with optical access points upstream of the compressor to visually identify condensation. The investigations were performed on two different Diesel engines—the JLR 3.0L SDV6 twin-turbo engine, as well as the 2.0L “Ingenium” engine.

Two-Stage Testing

The tests were performed in two stages: In stage one, steady-state mappings were created at various intake air and coolant temperatures down to -10°C. Here, two types of condensation were identified: A mild form of condensation, such as mist or fog, which mainly forms after mixing the exhaust gas with cold air. Regular visual checks of the compressor wheel blades have shown very little or no damage caused by this type of condensation. The intensity of the condensation increases in particular with falling intake air temperatures.
A more severe form of condensation is the formulation of droplets, which can cause severe damage to the blades of the compressor wheel. These droplets mainly condense directly in the LP-EGR cooler at low coolant temperatures, but their formation can also be witnessed after mixing the exhaust gas with fresh air at very low ambient air temperatures. With the mappings completed, it was possible to extend the boundary values for coolant and ambient air temperature to lower levels.
These results were validated with help of dynamic warm-up cycles such as NEDC or FTP75 in the in the second testing phase.

Varying Turbulences at Mixing Points

Both engines demonstrate very different behaviors regarding the formation of condensation. On the SDV6 engine, the exhaust mixes with fresh air at a very low turbulence level, resulting in a rather low rate of mixing upstream of the compressor. This rather laminar flow behavior seems to be beneficial for the avoidance of condensation, but also concentrates the condensation on the outside of the pipe, resulting in water droplets hitting the compressor wheel at high speeds. On the Ingenium engine, a high level of turbulence is present at the mixing point of exhaust gas and fresh air, resulting in a high level of mixing. Condensation can be witnessed on the Ingenium engine over the entire diameter of the pipe upstream of the compressor wheel at higher rates. When compared to SDV6, however, the damage to the compressor wheel is very limited, since most of the condensation hits the turbo at relatively low speeds in the center of the wheel.

Conclusion

Two conclusions can be drawn based on the above observation: On one hand, the LP-EGR operating window of the existing engines may be extended towards lower coolant and intake air temperatures if the results of a design verification endurance run do not indicate significant drawbacks. On the other hand, the results can be used to derive a design guide for future engine revisions.

Diagram - RDE

The measurement results of the climatic test bed show two types of condensation: a mild form of condensation and a more severe form which can cause severe damage.

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