Fire engine

A device, comprising:

• a vehicle frame;
• a liquid nitrogen storage tank comprising a first opening and a second opening;
• a liquid nitrogen conveying pipeline;
• a gasification device;
• a plurality of electric valves;
• a water pipe adapter;
• a liquid nitrogen spray gun comprising an input end;
• and
• a mixed spray gun comprising a first input end, a second input end, a liquid nitrogen nozzle, and a spray pipe;
• wherein:
• the liquid nitrogen storage tank is disposed on the vehicle frame;
• the second opening is disposed higher than the first opening relative to the gasification device;
• the liquid nitrogen conveying pipeline comprises at least a first pipeline and a second pipeline;
• the first pipeline connects the first opening of the liquid nitrogen storage tank, the gasification device, and the second opening of the liquid nitrogen storage tank sequentially in that order;
• the second pipeline connects the liquid nitrogen storage tank, the input end of the liquid nitrogen spray gun, and the first input end of the mixed spray gun sequentially in that order;
• the spray pipe comprises a contraction section, an expansion section, and an acceleration section which are connected to one another in that order;
• along a direction from the contraction section to the acceleration section, an inner diameter of the contraction section decreases, and an inner diameter of the expansion section increases;
• an inner diameter of the acceleration section is constant and equal to an outlet diameter of the expansion section;
• the liquid nitrogen nozzle communicates with the first input end and is disposed on an axial line of the contraction section;
• an outlet of the liquid nitrogen nozzle is coaxial with an outlet of the contraction section;
• an inlet of the second input end is connected to the water pipe adapter and an outlet of the second input end communicates with the contraction section;
• the water pipe adapter is connected to the inlet of the second input end via a water delivery pipeline;
• and
• the plurality of electric valves is disposed on the liquid nitrogen conveying pipeline and the water delivery pipeline.