Fuel injection control device, method and computer program for engine

A post-injection amount A required for forced regeneration of a particulate filter is calculated. A ratio B of a residual gas remaining in an inter-cylinder combustion chamber when post injection is performed and a wall surface adhering ratio C of a fuel adhering to the wall surface of a cylinder when the post-injection is performed are calculated. A post-injection amount D to be actually injected is calculated on the basis of the residual gas ratio B and the wall surface adhering ratio C, i.e., a ratio of a fuel which does not contribute to increase in exhaust temperature nor to the forced regeneration of the particulate filter and the already calculated required post-injection amount A. Then, the post-injection is performed with the calculated required injection amount D. Because the post-injection amount is determined by taking into consideration the fact that a part of a post-injected fuel may remain in a combustion chamber or adhere to the wall surface of a cylinder and thus does not contribute to increase in exhaust temperature, the precision of the forced regeneration of the particulate filter is improved and its effects can be exhibited.