Abstract: A cylinder causing an abnormal air-fuel ratio is specified. Injection ratio changing control for gradually changing a ratio between command injection quantities of two injectors of the abnormal cylinder while keeping the sum of the command injection quantities of the two injectors constant is performed on the abnormal cylinder. If the injection ratio changing control is performed under the same condition, a changing behavior of the actual sum injection quantity of the two injectors varies and a changing behavior of the air-fuel ratio varies depending on which one of the two injectors is abnormal. Therefore, the abnormal injector out of the two injectors is specified using a learning value of an air-fuel ratio feedback correction value based on an output of an exhaust gas sensor.

Abstract: A cylinder causing an abnormal air-fuel ratio is specified. Injection ratio changing control for gradually changing a ratio between command injection quantities of two injectors of the abnormal cylinder while keeping the sum of the command injection quantities of the two injectors constant is performed on the abnormal cylinder. If the injection ratio changing control is performed under the same condition, a changing behavior of the actual sum injection quantity of the two injectors varies and a changing behavior of the air-fuel ratio varies depending on which one of the two injectors is abnormal. Therefore, the abnormal injector out of the two injectors is specified using a learning value of an air-fuel ratio feedback correction value based on an output of an exhaust gas sensor.

Abstract: According to the invention a multi-layered furnace wall construction for industrial use is provided. The wall construction comprises an outermost iron shell layer, an innermost refractory fiber block layer and an intermediate layer interposed between the iron shell layer and the refractory fiber block layer. The refractory fiber block layer is secured to the intermediate layer by means of stud bolts and washers of ceramic material. The fibers constituting said refractory fiber block layer are oriented such that they extend in the direction substantially perpendicular to the surface plane of the furnace wall.