Bus Parking Heater Failure And Solutions(1)

- Dec 30, 2020-

Heater failure 1: It can ignite normally but extinguishes itself after tens of seconds.

Solution: The typical cause of this failure phenomenon is that the flame sensor of the burner accessory is dirty. The flame sensor is a photoresistor. When it is irradiated by light, its own resistance value decreases and presents a low impedance state. When there is no light, the resistance value rises and presents a high impedance state. The controller in the burner judges whether the combustion process continues according to the resistance value of the flame sensor. If the combustion stops and the flame sensor shows high impedance, the fuel supply will be stopped immediately to prevent the accumulation of unburned diesel. The flame sensor probe is located in the air duct of the burner, and its surface is easily dirty and loses its photosensitive function due to black smoke, backfire, and air supply dust. Check the sensor probe and clean its surface with alcohol or cleaning agent if necessary.

Heater failure 2: The fire is normal but the exhaust smoke is not normal. The diesel fuel injected into the burner is mixed and burned. When the air volume is appropriate, the atomized CO2 and steam exhaust are colorless. 

Solution: When the air supply is insufficient, the diesel will be incompletely burned to produce CO and carbon particles, resulting in black smoke from the exhaust. However, if the air intake is too large, the strong wind may blow away the fuel mist that is too late to burn. White smoke is discharged. The common cause of black smoke from exhaust is that the opening of the burning air intake door is too small, and the cause of white smoke is that the air intake door is too open. In both cases, the air intake door should be readjusted. When adjusting, you can adjust the opening of the damper while observing the exhaust smoke color until the exhaust smoke color is close to colorless. Another reason for black smoke from exhaust is poor diesel atomization. The oil mist contains large droplets, which cannot be fully mixed with air, and black smoke is generated due to incomplete local combustion.

The reasons for poor diesel atomization are:

1) The aging or clogging of the nozzle severely reduces its atomization capacity.

2) The output pressure of the fuel pump is too high or too low. If the fuel pump pressure is too low, the nozzle output pressure will be low. Of course, the atomization effect is poor, but the fuel pump output pressure is too high, which will also cause low injection pressure. This is because the fuel delivery volume of the fuel pump is inversely proportional to the fuel delivery pressure. If the fuel pressure is too high, the fuel output will inevitably decrease. Because the orifice of the nozzle is constant, the pressure difference between the two ends of the nozzle is reduced, resulting in spray mist Poor chemistry is often accompanied by black smoke.

  The fuel output pressure of the fuel pump can be adjusted according to the exhaust smoke color. Turn the pressure adjusting screw clockwise to increase the pressure and decrease the fuel output; otherwise, the pressure decreases and the fuel output increases. The normal range of fuel pump pressure is 0.98~, and it cannot be adjusted at will during use.

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