The invention relates to a subcritical vapor auxiliary work done
gasoline engine which comprises a water
injector in a cylinder of the
gasoline engine, wherein, the water
injector comprises a water tank, an
electric control unit, and water pumps, a water guideway, a water injection
nozzle and a temperature sensor which are controlled by the
electric control unit. The water
injector is characterized in that the water pumps comprise a low pressure water pump and a
high pressure water pump pressurizing water to be above 200bar, the low pressure water pump is arranged in the water tank and is communicated with the
high pressure water pump, the
high pressure water pump is communicated with the water guideway by a
high pressure water pipe, the water injection
nozzle is communicated with the water guideway, and a water injection opening extends into a
combustion chamber of the
gasoline engine. The gasoline engine also comprises a gasoline engine
exhaust pipe used for heating water to above 250 DEG C and not more than 374.2 DEG C, and a
high pressure water pipe penetrates through the
exhaust pipe and then is communicated with the water guideway. The gasoline engine utilizes the
waste heat of engine
tail gas to do work circularly, thereby saving oil; the temperature of water injected into the cylinder is in a subcritical state, and the water is instantaneously vaporized in the cylinder under the pressure condition, thereby increasing the explosion pressure of the cylinder; and the torque output and the power are improved under the premise that the oil injection amount is not increased.