1. 5th International Seminar on ORC
Athens, 09/09/2019
ASSESSING FUEL CONSUMPTION REDUCTION OF REVERCYCLE A REVERSIBLE MOBILE AIR CONDITIONING/ ORGANIC RANKINE CYCLE SYSTEM
Luca Di Cairano1, Wissam Bou Nader2, Florent Breque1, Maroun Nemer1
1MINES ParisTech, PSL Research University, Center for energy Efficiency of Systems, Palaiseau, FR 2Groupe PSA, Centre technique de Vélizy, Vélizy, FR

2. Outline Context Global warming Engine energy balance
ORC in a passenger car
ReverCycle
The concept
Operating modes
Fuel economy
Global dynamic model of the vehicle
ORC model
Optimal speed ratios in ORC mode
ReverCycle fuel economy: methodology
MAC activation time
ReverCycle fuel economy: results
Conclusions
Future Work
References

3. Global warming In Europe
Passenger cars are responsible for 60% of the total transport sector emissions.
(Source: European Environment Agency)
Regulators are imposing strict emission limits to car manufacturers
Transport sector
CO2 emissions
Time

4. Engine Energy Balance Rule of thumb Waste Heat Brake Power
Due to this important amount of available energy Waste Heat Recovery systems have gained major interest.
TEG
Turbocompounding
Thermoacoustic
Rankine Cycle

5. CES concept: ReverCycle
ORC in a passenger car
In a passenger car:
compactness requirements
dynamic working conditions
strong attention to system cost
Automotive ORC development implies:
A low cost and compact design
Assessment of fuel economy on dynamic working conditions
CES concept: ReverCycle

6. Outline Context Global warming Engine energy balance
ORC in a passenger car
ReverCycle
The concept
Operating modes
Fuel economy
Global dynamic model of the vehicle
ORC model
Optimal speed ratios in ORC mode
ReverCycle fuel economy: methodology
MAC activation time
ReverCycle fuel economy: results
Conclusions
Future Work
References

7. The concept MAC ORC Two mutualized components: ReverCycle = MAC +pump
+ heat exchanger
+ valves
Reversible
machine
Standard MAC condenser
Waste heat source: Engine Coolant
Exergy
R134a/R1234yf
Automotive scroll compressor can be easily converted into a reversible machine

8. ReverCycle operating modes
MAC
ORC
ReverCycle can operate as a MAC or as an ORC.
Switching between modes: 2 automatic valves.
ORC pump and compressor/expander are mechanically coupled to engine shaft.
(Reversing gearbox for expander)

9. Outline Context Global warming Engine energy balance
ORC in a passenger car
ReverCycle
The concept
Operating modes
Fuel economy
Global dynamic model of the vehicle
ORC model
Optimal speed ratios in ORC mode
ReverCycle fuel economy: methodology
MAC activation time
ReverCycle fuel economy: results
Conclusions
Future Work
References

10. Global dynamic model of the vehicle
Step by step development of a vehicle model.
Powertrain model (Table based engine)
Engine cooling system model (Table based cabin heater)

11. ReverCycle adds power to the engine shaft
ORC model
ThermoCycle Library (Quoilin et al, 2014) + CoolProp Library (Bell et al, 2014)
ReverCycle adds power to the engine shaft =
Fuel economy

12. Optimal speed ratios in ORC mode
ORC average cycle efficiency as a function of speed ratios.
A speed ratio has to be defined:
Between pump and engine shaft
Between expander and engine shaft
Pump/Engine 0.6
Pump/Engine 1
Pump/Engine 1.4
Expander/Engine 0.24
4.2 %
4.8 %
4.1 %
Expander/Engine 0.4
2.5%
5 %
Expander/Engine 0.56
2 %
3.9 %
4.2%
The final choice is a compromise between cycle efficiency and average expander inlet vapor quality (avoid two phase expansion)

13. ReverCycle fuel economy: Methodology
Reference driving cycle: WLTC
Two initial conditions:
Hot start: engine temperature is 85°C
Cold start: engine temperature is equal to ambient temperature
ReverCycle (ORC) is strongly affected by ambient temperature :
Engine warm up
ORC efficiency
Waste heat energy is limited by cabin heater demand
ORC availability is limited by MAC activation time
The global vehicle model
takes into account these effects

14. MAC activation time
A cabin thermal model (Benouali, 2002) is coupled to a thermal comfort model (Fanger, 1982) to provide the percentage of drivers that will turn on the MAC entering the cabin after one hour thermal soak.
Cabin model validation on (Marcos et al, 2014) exp. results
City
MAC activation time
Paris
21%
Moscow
16%
Valencia
41%
Brasilia
59%
Annual simulation on 4 different climatic regions (Paris, Moscow, Valencia, Brasilia).

15. ReverCycle fuel economy: Results
Fully available ORC
+20% Fuel economy
(E.g. Paris Hot Start 2% ->2.4%)
2 x Weight
Higher cost
City
HOT START
Fuel economy
COLD START
Paris 2%
1.3%
Moscow
1.7%
1.1%
Valencia
1.2%
Brasilia 1%
Best climatic region

16. Outline Context Global warming Engine energy balance
ORC in a passenger car
ReverCycle
The concept
Operating modes
Fuel economy
Global dynamic model of the vehicle
ORC model
Optimal speed ratios in ORC mode
ReverCycle fuel economy: methodology
MAC activation time
ReverCycle fuel economy: results
Conclusions
Future Work
References

17. Conclusions ReverCycle is a low cost and compact solution.
This study was able to:
Assess ReverCycle ORC mode availability (≈80% in a temperate region, ≈ 40% hot region)
Assess the annual average fuel economy on a WLTC ( 1-2% fuel economy)
Define the best climatic region for ReverCycle ROI (temperate region)

18. Future Work Add an ejector to ReverCycle MAC/ORC/ERC
To increase WHR activation time
ReverCycle Proof of Concept
MAC
ORC
ERC

19. References
Bell, I. et al. (2014) , ‘ Pure- and Pseudo-Pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library CoolProp’, Ind. Eng. Chem. Res., 53, pp
Benouali, J., 2002, Etude et minimisation des consommations des systèmes de climatisation automobile, PhD diss., Ecole des Mines de Paris.
Fanger. P.O., 1982, Thermal Comfort. Malabar FL: Robet E. Krieger Publishing Company
Marcos, D. et al. (2014) ‘The development and validation of a thermal model for the cabin of a vehicle’, Applied Thermal Engineering. Elsevier Ltd, 66(1–2), pp. 646–656. doi: /j.applthermaleng
Quoilin, S. et al. (2014) , ‘ThermoCycle: A Modelica library for the simulation of thermodynamic systems’, Proceedings of the 10th International Modelica Conference, pp