To provide control technology for a diesel engine capable of inhibiting formation of particulate matter such as soot even if fuel of high bio-fuel concentration is used and of creating a desired reducing atmosphere in an exhaust emission control catalyst.
ECU 100 judges whether bio-fuel concentration in fuel is not less than a predetermined judgment concentration or not. When it is judged that bio-fuel concentration exceeds the judgment concentration, the reducing atmosphere containing reducing agent is created at the exhaust emission control catalyst 55 by fuel from a fuel injection device 80 instead of fuel from an exhaust gas fuel addition valve 88. Since fuel from the fuel injection device 80 is injected in a high temperature cylinder and is contained in exhaust gas from the cylinder, formation of particulate matter such as soot can be inhibited and the desired reducing atmosphere can be created at the exhaust emission control catalyst 55 by sufficiently vaporizing fuel as the reducing agent even when fuel of bio-fuel concentration exceeding the judgment concentration is used.
TANIGUCHI SATOSHI
YOSHIDA KAORI
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