Catalyst warm up control for diesel engine

Diesel engine is operated in a first warm-up mode in an early warm-up period after startup so as to accelerate activation of the catalyst, and then in a second warm-up mode in a late warm-up period after the early warm-up period so as to maintain activity of the catalyst. The first warm-up mode provides more energy to the catalyst with exhaust gases than the normal operation mode of the diesel engine. The second warm-up mode provides exhaust gases of higher temperature to the catalyst than the normal operation mode.