High-pressure SCR on two-stroke engines

High-pressure selective catalytic reduction places the reactor upstream of the turbocharger on a two-stroke engine, taking exhaust at turbine inlet temperature and pressure. Low-pressure SCR places it downstream, after the turbine, where the gas is several hundred degrees cooler.

The choice is set by temperature, not by convenience. A vanadium-based catalyst needs a minimum inlet temperature to run the reaction, and that minimum rises with fuel sulphur because ammonium bisulphate forms and fouls the catalyst below it. On a large two-stroke burning residual fuel, the post-turbine temperature at part load may not reach it, and the high-pressure arrangement is the answer. Resolution MEPC.291(71) requires the allowable exhaust gas temperature range at the chamber inlet and the maximum allowable fuel sulphur content to be documented for the approved system.

The full article will set out both arrangements with their control implications, the reactor bypass and warm-up strategies, the pressure loss allowance across the chamber and ducting, catalyst deterioration and block exchange, and the interaction with an exhaust gas cleaning system in the same uptake.