SCR (selective catalytic reduction) injection system without pneumatic assistance

The invention discloses an SCR (selective catalytic reduction) injection system without pneumatic assistance. The SCR injection system aims to overcome shortcomings of complicated structure, high manufacturing cost and poor atomizing effect for urea solution injected to an exhaust pipe of an existing SCR injection system. The SCR injection system comprises a urea adding device, an injection device, a control device, an SCR reaction device and a cooling device; the control device is electrically connected with the urea adding device and the injection device, the injection device is connected with the SCR reaction device, both the cooling device and the urea adding device are connected with the injection device, the injection device comprises a nozzle, the nozzle comprises a connecting seat and a needle valve assembly, the upper end of the connecting seat is connected with a support seat, a return spring is arranged in the support seat, and an electromagnet is sleeved on the outside of the support seat; and the needle valve assembly comprises a needle valve body and a needle valve, an electromagnetic armature is arranged above the needle valve body, a needle valve seat is fixedly connected to the lower end of the needle valve body, an injection hole is arranged on the needle valve seat, the lower end of the needle valve is matched with the injection hole and is hermetically connected with the injection hole, an atomization cyclone sheet is arranged on the needle valve seat, and a guide plate is arranged on the atomization cyclone sheet.