Investigation of High Internal Residual Gas Rates in Rich Operating Mode for Diesel Lean NOx Trap Regeneration 2021-01-0592
For the regeneration of the Lean NOx Trap (LNT) a rich air-to-fuel ratio must be generated. This operation is very critical and has low combustion stability, especially in low load operation. A certain minimum engine load is always required for the regeneration phase. In the Real Driving Emissions this minimum engine load can be undercut over a long period of time. Hence, a reliable regeneration phase is not possible.
The aim of these investigations is to extend the engine map range in which regeneration is possible towards lower loads. This is done by means of a variable valve train with second exhaust valve lift, which increases the internal residual gas amount. This in turns increases the temperature at start of combustion in the cylinder. Especially at low load and low combustion stability this leads to a stabilization of the combustion process. This advantage in combustion stability can be used for a reduction of the minimum engine load.
The approach of this work consists of investigations on the engine test bench and accompanying simulations. The combustion process is thermodynamically examined and evaluated on the engine test bench using pressure trace and gas exchange analysis, including a residual gas model.