EXHAUST EMISSION CONTROL SYSTEM

摘要

PROBLEM TO BE SOLVED: To solve such a problem that an SCR (Selective Catalytic Reduction) type exhaust emission control system may cause the accumulation of deposits resulting from reductant in an exhaust pipe, or a reduction in the eliminating efficiency of nitrogen oxide or the worsening of fuel economy.SOLUTION: The exhaust emission control system of the present invention includes a reductant injection valve 24b for injecting reductant R toward a member facing an exhaust passage 18a, and an SCRF (Selective Catalytic Reduction Filter) 24c arranged downstream of the reductant injection valve 24b in an exhaust passage 18a, and is used for reducing nitrogen oxide included in exhaust gas from an engine 10. The exhaust emission control system further includes means 16h for calculating the particle sizes of the reductant R after colliding with the member, and calculating a time trequired for vaporizing the reductant R injected into the exhaust passage 18a on the basis of the particle sizes of the reductant R, and means 16i for changing the conditions of injecting the reductant R performed by the reductant injection valve 24b so that, when a calculated time trequired for vaporizing the reductant R is longer than an interval tfor injecting the reductant R performed by the reductant injection valve 24b, the time trequired for vaporizing the reductant becomes equal to or less than the interval tfor injecting the reductant R.