18 May 2017

O.3.2.4 Compressor Explosion Accident at Pump-Down of Air Conditioners

These days the problem of global warming is becoming more serious and low GWP is demanded for refrigerants used for heat pumps. R1234yf and R32 are promising candidates of new lower-GWP refrigerants; however, they have mild flammability. Therefore, a safety assessment of flammable refrigerants is required.
This study focuses on compressor explosion accidents at the pump-down of separate type air conditioners. Pump-down is an operation to accumulate the entire refrigerant in the outdoor unit by closing the outlet valve of the outdoor unit and compulsorily driving the compressor. If the penetration of air into the refrigerant tube occurs by an operation error, both pressure and temperature inside the compressor would increase. The lubricating oil in the compressor may be self-ignited, and cause diesel explosion.
In this research, we reproduced the diesel explosion and examined its characteristics. The mixture of air, refrigerant and oil were sucked into the cylinder, and were compressed by a compressor, which was simulated by a small-scale engine. R1234yf, R32, R410A and R22 were tested as refrigerants, and PAG oil and POE oil were tested as the lubricating oils. We changed the concentration of the oil, and measured the effect of the oil on the explosion.
It was revealed that flammable range was widely changed by different lubrication oils, which suggested that properties of not only the refrigerant but also the oil were important factors for the accident at the pump-down. The accident probability can be decreased by adjusting the flammability of the lubricating oil.