1.7

Diesel Combustion of Oil and Refrigerant
Mixture during Pump Down of AirConditioners
ICR 2015 Workshop on Risk Assessment of Mildly
Flammable Refrigerants
August 20, 2015

Chaobin DANG, Tomohiro HIGASHI and Eiji HIHARA
Department of Human and Engineered Environmental Studies,
The University of Tokyo11. BACKGROUND

2

1.BACKGROUND

1-1. Refrigerants for Air Conditioner

Transition of refrigerants in air conditioning Applications

Ammonia

CFC(Chlorofluorocarbon)
HCFC(Hydro-CFC)

HFC(Hydrofluorocarbon)
・R410A (CH2F2 + C2HF5)・R134a (C2H2F4)・R11 (CFCl3)
・R22 (CHF2Cl)

Concern overtoxicity and flammability

Concern overhigh ODP

Concern overhigh GWPNew Low GWP Refrigerants
・R32 (CH2F2)・R1234yf (CH=CF-CF3)・ etc※mildly flammable
Low Flammability ⇔ Low GWP (trade-off)Ozone depletion material reduction schedulebased on Montreal Protocol(Ministry of the Environment)⇒New low GWP refrigerants (R1234yf, R32)
are drawing increasing attention,3
but are mildly flammable1.BACKGROUND

1-2. Heat Pump and Pump Down
※Cooling condition

Evaporator

Refrigerant
FlowIndoor
Unit
Condenser

CompressorOutdoorUnitValve
膨張弁

PUMP DOWN
Recovering the refrigerant from indoor unit
as liquid and store it in the outdoor unit 4

1.BACKGROUND

1-3. Accident during Pump Down••

Explosion of outdoor unit happened during pump down.
According to report of Tokyo metropolitan government,
the accidents were caused by the air leakage into the refrigerant tube
by operation error during pump down. (Diesel explosion)（Tokyo metropolitan government）

How to operate pump down

Explosion accident(エアコン処分。com)(Tokyo metropolitan government)

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1.BACKGROUND

1-4.Purpouse

Background①
Flammability of Refrigerants
・Low GWP
・Mild flammability

Background②
Accident during Pump Down
・Accidents happen during pump down
・No research have been conducted
about conditions of explosion

PURPOUSE
1.

2.

To investigate the conditions of self explosion of air,refrigerant and lubricating oil mixture in the compressorof an air conditioner.
To estimate the safety of the new refrigerants
by comparing to conventional refrigerants
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2. MATERIALS AND METHODS

7

2.MATERIALS AND METHODS

2-1.Experimental Apparatus

Refrigerant
line
Refrigerant

Scrubber
Mass flow
controller

cylinderFT-IR
Gas cell
Heater 1

Air line

Compressor(model engine)
Dehumidifier
Air compressor

Lubricating
oil line

Mass flow
meter

Mass flow
controller
Oil injection
systemHeater 2T

Motor

P

Stroke sensor

EncoderCompressor(model engine)

Oil tank

Stroke volume： 25.42 cc
Compression ratio：16.0
Four-stroke engine
8

2.MATERIALS AND METHODS

2-1. Experimental Conditions• Experiment 1
Air + Oil• Experiment 2
Air + Refrigerant• Experiment 3
Air + Refrigerant + Oil

9

2.MATERIALS AND METHODS

2-2.Experimental Methods① Control the flow ratio of the air, refrigerant
and the lubricating oil independently,
Injectormix them, adjust the inlet temperature

Experiment apparatus

・Oil is sprayed into air/refrigerant mixture.
・Oil flow ratio was controlled by injection time.

②Adiabatic compression by the engine,
self ignition inside.
MotorEngine
Pressure sensor

・Engine is driven by motor.
・Encoder measures clank angle.
・Pressure inside engine is measured.

Encoder③FT-IR analyzes the exhaust gas.
・Infrared absorption spectrum.
・Take BKG before experiment.
Example of BKG
FT-IR10

2.MATERIALS AND METHODS

2-3. Experimental Parameters••••••Engine rotation speed: 1500 [rpm]
Inlet gas mixture temperature: 260 [℃]
Refrigerants：
R1234yf, R32 (Low GWP refrigerants, mildly flammable)
R410A (conventional, nonflammable, mixture) ※R32： R125 = 1:1
R134a, R22, R125 (Nonflammable pure refrigerants)
N2 (Inert gas)
Refrigerant concentration: 0 to 100 [vol%]Oil flow rate: 0 (without oil),
2.295×10-4 [L/min] ( injection time: 0.7msec per one time)(stoichiometric air-fuel ratio based on the air flow ratio when refrigerant
concentration is 0 %)Injection timing: 90°(crank angle of the engine)※Oil flow ratio is kept constant at any refrigerant concentration.
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2.MATERIALS AND METHODS

2-4. Appearance of Experiment 1Engine

Exhaust gas (to FT-IR)

Intake port

MotorEncoder

Oil injector

122.MATERIALS AND METHODS

2-5. Appearance of Experiment 2
Stroke sensor
Intake valve

to FT-IR
Exhaustvalve

Intake port

Intakevalve

Air refrigerant
mixtureto FT-IREngine

4 cycle engine ⇒720°for total stroke
Stroke sensor detects intake valve’s opening during intake stroke.
⇒Distinguish 0 to 360°,
Control injection timing with encoder.

Injector※Timing of Injection
90 to 96.3°(crank angle)
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3. RESULTS AND ANALYSIS

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3.RESULTS AND ANALYSIS

3-1. Pressure Change for Air-Oil Mixture

2.5

Pressure[MPa]2without oilwith oil

1.5
10.5
0180

240

300

360

420

480

540

Crank Angle[degree]
B.D.C
B.D.C
(Initial compressingpoint)

T.D.C(Maximum compressing point)

TDC: Top Dead Center
BDC: Bottom Dead Center

・Combustion occurred with oil injection
・Pressure increased
・Loud noise and strong vibration
15→Lubricating oil self-ignited

3.RESULTS AND ANALYSIS

3-2. Pressure at Different Refrigerant Concentrations
R1234yf, with oil

R1234yf, without oil
66At low refrigerant concentration,pressure rises with the presence of oil
54

Pressure[MPa]Pressure[MPa]5343

2
At high refrigerant concentration,
no combustion occurred
even though with
1 oil

2100180240300360
420
Crank Angle[degree]
0%

10%

480

540

65%

・Intense combustion at low concentration
・Black exhaust gas

180240300
360
420
Crank Angle[degree]
0%20%

480

540

65%

・No combustion occurred without oil
・Pressure decreased
as concentration increased
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3.RESULTS AND ANALYSIS

3-3. Analysis of Exhaust Gas 1

R1234yf, with oil, 60%

FT-IR

R1234yf(1800~1000cm-1)

R1234yf, with oil, 10%
HF(4200~3600cm-1)

Gas cell of FT-IR
COF2(1980~1880cm-1)

C3H2F4 (R1234yf) + 5/2 O2 + x H2O
HF and COF2 were produced by→(2+x) CO2 + (2+2x) HF + (1-x) COF2 combustion of refrigerant17

3.RESULTS AND ANALYSIS

3-4. Analysis of Exhaust Gas 2

R32, with oil, 30%R32: CH2F2

R22, with oil, 20%

HF

COF2

R22: CHF2ClHCl(3100–2600 cm-1)

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3.RESULTS AND ANALYSIS

3-5. Differences in Refrigerant Concentration 1P_max[‐]

3Low concentration→Combustion, pressure increase, production of HF

0.6

2.5

0.5

2

0.4

1.5

0.3

1

0.2

0.5

0.1

0

Air100%

Cons_HF[vol%]R1234yf

00102030

with oil

40506070
Conc_ref[vol%]without oil
R1234yf P_th

Air leakage into refrigerant

80
HF[vol%]90100

Refrigeran100%(normal operation)

Theoretical pressure rise
100100High concentration→No combustion, similar to without oilLess HF produced
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3.RESULTS AND ANALYSIS

3-6. Differences in Refrigerant Concentration 2R32 (CH2F2)

R410A (CH2F2+C2HF5)

3

0.6

3

0.6

2.5

0.5

2

0.4

2

0.4

1.5

0.3

1.5

0.3

1

0.2

1

0.2

0.5

0.1

0.5

0.1

00

00

0

20

4060
Conc_ref[vol%]

80

100

020

4060

80

100

Conc_ref[vol%]20

HF[vol%]0.5

P_max[‐]

2.5

HF[vol%]P_max[‐]

c.f. accidents of conventional airconditioners

3.RESULTS AND ANALYSIS

3-7. Differences in Refrigerant Concentration 30.6

30.6

2.5

0.5

2.5

0.5

20.4

20.4

1.5

0.3

1.5

0.3

10.2

10.2

0.5

0.1

0.5

0.1

00000204060
Conc_ref[vol%]

80

100

P_max[‐]

30204060

80100Conc_ref[vol%]21

HF[vol%]R134a (C2H2F4)

HF[vol%]P_max[‐]

R22 (CHF2Cl)

3.RESULTS AND ANALYSIS

3-8. Differences in Refrigerant Concentration 4N2
0.6

32.5

0.5

2.5

20.4

21.5

0.3

10.2

10.5

0.1

0.5

0000204060
Conc_ref[vol%]

80

100

P_max[‐]

3HF[vol%]

P_max[‐]

R125 (C2HF5)

1.5

020

40
60
80
Conc_ref[vol%]10022

4. CONCLUSION

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4. Conclusion
 Accidents during pump down are caused by the diesel
combustion of a mixture of air, refrigerant and lubricating oil
 Combustion induces pressure rise
 【air + refrigerant】(no combustion)< 【air + oil】 < 【air + oil + refrigerant】
 HF was observed when combustion occurred HF is a production of refrigerant combustion
 Refrigerant itself was burned
 Self-ignition of lubricating oil → Combustion of refrigerant→ Pressure increase Conventional refrigerants (R410A, R22) were compared with newrefrigerants (R1234yf, R32)
 No significant difference observed in terms of flammable rangeand pressure24

Acknowledgements
This study has been conducted a part of research projecton the “Technology Development of High-efficiency Nonfluorinated Air Conditioning Systems” conducted by New
Energy and Industrial Technology Development
Organization (NEDO)

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Thank you for your attention!

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