Method for controlling the operation of a hydrogen combustion engine system of a vehicle

A hydrogen combustion engine system for a vehicle, the hydrogen combustion engine system comprising a hydrogen combustion engine and an exhaust aftertreatment system, EATS, configured to reduce emissions in the engine exhausts, the EATS comprising a selective catalyst reduction, SCR, catalyst and an ammonia slip catalyst, ASC, arranged downstream of the SCR catalyst, wherein the hydrogen combustion engine system comprises a control unit configured to:

• identify a regeneration time window for performing regeneration of the ASC, the regeneration time window being defined at least by that the temperature of the EATS is above a predetermined lower limit and that the temperature of the SCR catalyst is below a predetermined upper limit;
• in response of identifying the regeneration time window, instruct the hydrogen combustion engine to operate in an H2 exhaust excess mode defined by an amount of unburnt H2 of at least 1.5 mol % in the engine exhaust for using the unburnt H2 in the engine exhausts to regenerate the ASC by reaching a regeneration temperature of at least 500° C.