Underground coal mines’ transport vehicles powered by diesel engines need exhaust gas treatment. In order to keep the temperature of the diesel engine below 70°C, the exhaust gas of the diesel engine should be passed into the water washing chamber . On the other hand, during the operation of the diesel engine, since the water in water washing chamber is continuously taken out, the water level in the washing tank will become lower and lower, and when the water level in the water washing chamber is too low, the temperature of the diesel engine will be reduced. When the temperature exceeds 70°C, a supplementary water tank needs to be added, and Water-replenishing tank can be supplemented into the Water washing chamber.