High pressure EGR provides NOx emission reduction even at low exhaust temperatures. To maintain a safe EGR system operation over a required lifetime, the EGR cooler fouling must not exceed an allowable level, even if the engine is operated under worst-case conditions.
A reliable fouling simulation model represents a valuable tool in the engine development process, which validates operating and calibration strategies regarding fouling tendency, helping to avoid fouling issues in a late development phase close to series production.
Long-chained hydrocarbons in the exhaust gas essentially impact the fouling layer formation. Therefore, a simulation model requires reliable input data especially regarding mass flow of long-chained hydrocarbons transported into the cooler.
There is a huge number of different hydrocarbon species in the exhaust gas, but their individual concentration typically is very low, close to the detection limit of standard in-situ measurement equipment like GC-MS.
Therefore, a new measurement and analysis approach has been developed, where the exhaust gas is guided to a metal foam collector, in which HC`s are deposited. The probe is then analyzed in a suited thermogravimetrical system (TGA) in nitrogen atmosphere, temperature range 25°C to 650°C. Analyzing the TGA curve, HC concentration data for 6 different boiling temperature ranges are obtained, provided to an adapted 1-d fouling simulation model.
Using these data along with further input parameters like cooler geometry, gas temperature, pressure, flow, particle size distribution and coolant temperature, the simulation model has proven as a suitable tool to predict the fouling and identify engine settings for fouling reduction.