A piston expander for exhaust heat recovery on heavy commercial vehicles

Transcription

1 RANKINE TECHNOLOGIES A piston expander for exhaust heat recovery on heavy commercial vehicles Speaker&author: Rémi Daccord CTO & Founder remi.daccord@exoes.com Co-author: Matthieu Sager Simulation Engineer

2 EXOES All rights reserved Exoès at a glance

3 A seasoned team EXOES team coming from the automotive or AC compressor industry EXOES board of advisors Pierre LECOCQ Christian BOGEAT Patrick BUFFET Automotive industry Oil & gas EXOES technical advisors Dr. Mathias Woydt Tribology BAM - Germany Dr. Jean-Louis Ligier Mechanics Comatec - Switzerland Laurent Joly Costing Bucephale - France 3

4 Exoès offers: prototypes, simulations, tests & benches Extract of customers: EXOES offers: 4

5 Links to the academic world Exoès Bordeaux, France Ethanol test bench 230 kw University of Liège Belgium Partnership r245fa test benche 50 kw University of Valencia Spain Partnership Ethanol test benches 30 kw / 200 kw 5

6 Example of an ORC layout Focus on exhaust heat recovery only 2.5 to 5% fuel cuts are expected on real trucks 1 4 1: Main radiator 2: ICE 3: After-treatment Vapor Liquid Typical Rankine layout for piston expander 3 5 4: Exhaust bypass valve 5: Exhaust evaporator 6: EGR evaporator 7: Distribution valves 8: Bypass valve 9: Expander 10: Condenser 11: Filter 12: Charge pump 13: Cooling flow valve(s) 14: Expansion vessel to be controlled 6

7 EXOES All rights reserved A piston expander for exhaust heat recovery

8 At last, we did it! 2015: New compact expander ready for truck integration! 2014: double acting pistons & lubrication concept 2013 : swashplate architecture & lubricant 2012 : Inlet valves & materials 8

9 Exoès piston expander technology Double acting swashplate technology 6 pistons 300 cm3 Inlet poppet valves and exhaust ports Dedicated lubricant and integrated oil pump 9

10 New expander generation 2016 Tests are currently beginning in our lab Speed range 1,500-4,500 RPM Shaft power range <20 kw Eff. Is. efficiency range Typ % Expander size W215xH215xL350mm Weight <18kg Oil circulation rate Typ. 5% Outlet pressures 1-3barA Inlet pressures bara Vapor quality Saturated accepted Nominal pressure ratios Transmission Gear/Pulley, Clutch NO 10

11 Inlet Pressure (bara) Inlet Pressure (bara) Efficiency forecast Simulations of our new expander : Thermal Efficiency [%] Fluid : EtOH 95.5% Outlet Pressure = 1 bara Overheat = 30 C Effective Isentropic Efficiency [%] Fluid : EtOH 95.5% Outlet Pressure = 1 bara 56 Overheat = 30 C Speed (rpm) Speed (rpm)

12 EXOES All rights reserved Testdata

13 Former EVE-T: tests data sample Example of test data Performances measure on steady points with fluid Ethanol 95.5% - Water 4.5% Assumption 5% Oil Circulating Rate (OCR) Inlet Inlet Outlet Shaft Mass Outlet pts Speed Pressure Temp. Pressure Power Flow Temp. bara C bara RPM kw g/s C , , , , , , , , ,

14 Efficiencies by EXOES Without OCR: Pure isentropic efficiency: η is = h s h d h s h d,is Effective isentropic efficiency: η eff,is = W shaft M.(h s h d,is ) Energetic efficiency: η e = η eff,is η is < 1 Thermal efficiency: η th = W shaft M.(h ev,out h ev,in ) We take a subcooling of 5 C at pump inlet to assess the thermal efficiency With OCR: OCR is a mass percentage Pure isentropic efficiency: η is = M.(1 OCR).(h s h d )+( M.OCR ).(P ρ s P d ) oil Effective isentropic efficiency: η eff,is = Energetic efficiency: η e = η eff,is η is Thermal efficiency: η th = M.(1 OCR).(h s h d,is )+( M.OCR ρ oil ).(P s P d ) W shaft M.(1 OCR).(h s h d,is )+( M.OCR ρ oil ).(P s P d ) W shaft M. 1 OCR.(h ev,out h ev,in )+M.OCR.C P,oil. T 14

15 Former EVE-T: efficiencies Performances measure on steady points with fluid Ethanol 95.5% - Water 4.5% Assumption 5%OCR pts Pure Isentropic efficiency Effective Isentropic efficiency Energetic efficiency Evaporator inlet temp. Thermal efficiency % % % C % 1 73% 54% 74% % 3 66% 52% 78% % 6 71% 56% 79% % 9 75% 55% 74% % Comparison of expanders must be carefully made Thermal efficiency is a good indicator, though it is not enough: the vapor pressure changes the vapor power recovered from exhaust gases (for EtOH at least) and the pump consumption 15

16 Impact of OCR Volume flow measured after the pump by a paddlewheel style flowmeter Volume to mass conversion through an OCR-adjusted density assumption OCR not measured in realtime assessed with sample analysis Before test: OCR 0% After test: OCR 8.5% (without oil traps content) Pt 9 Flow Density Massflow (incl. OCR) Pure Isentropic efficiency Effective Isentropic efficiency Energetic efficiency Thermal efficiency m3/s kg/m3 g/s % % % % OCR 0% OCR 5% OCR 8.5% Error 0% <±1% <±1% 0% ±2% ±2% ±2% 16

17 EXOES All rights reserved Simulation

18 Cylinder pressure [bara] Matlab model architecture Exoès has developed a matlab model for its expander technology: RPM Ẇ shaft Matlab Expander model Inlet: Friction (i) Q fric2(i) Outlet: Ṁ P in T in Energy balance Ṁ leak in (i) Q in(i) Ṁ in(i) ΔP in(i) Ẇ load(i) Expansion chamber (i): Volume (i) Valve timing (i) Energy balance (i) 5 0 Mass balance (i) 45 Q fric1(i) PV diagram cylinder head exhaust manifold expansion compression intake phase exhaust phase Cylinder volume [m3] x 10-5 Ṁ leak out (i) Q out(i) Ṁ out(i) ΔP out(i) Energy balance Ṁ T out P out Q cool T wall Q amb Output Input (i) : discretization per half shaft angle T amb 18

19 Mechanical model Each mechanical link is simulated: Friction of the shoe on the plate and friction of the piston rings on the cylinder represent the major mechanical losses Modeling and calibration of the friction of the shoe on plate have been critical for a good accuracy, based on 2D discretization of the oil film between the shoe and the plate: 41% 44% EVE kinematic scheme, with: NRB: Needle Roller Bearing TDC: Top Dead Center BDC : Bottom Dead Center TB: Thrust bearing G: Guide 19

20 Calculated mass flow [g/s] Calculated mechanical power [kw] Calculated outlet temperature [ C] Model calibration All the loss models have to be calibrated: Internal leaks Heat transfers Pressure drops Friction Calibration against: Literature and supplier data Organ test benches Expander test data 80 y = x +/- 5% y = x +/- 2 C Measured outlet temperature [ C] Measured mass flow [g/s] 5 Calibration Data Extrapolation Data Measured mechanical power [kw] 20

21 Simulated eff. is. efficiency [%] Model Calibration The model is able to predict Massflow, Power and outlet enthalpy with an accuracy of +-5% and even better for the efficiencies: y = x +/- 2% Measured eff. is. efficiency [%]

22 Effective Isentropic Efficiency [%] Losses analysis on former EVE-T Losses distribution in EVE-T Speed = 2,400 rpm ; Overheat = 20 C ; Outlet Pressure = 1 bara Current design point Former design point Inlet Pressure [bara] Without Leaks Without Friction Without Heat Transfers All Losses The new design had to reduce the heat transfers 22

23 EXOES All rights reserved Fuel savings assessment with different fluids Fluid choice still not reached a consensus: Ethanol / r1233zd used to be the main trends Hydrocarbons: cyclopentane recently reactivated

24 Fuel benefit assessment Input data - design point Units Value Exhaust inlet temp. C 300 Exhaust massflow kg/s 0.15 Min. exhaust outlet temp. C 120 Min pinch value C 20 EGR inlet temp. C 460 EGR massflow kg/s 0.06 EGR outlet temp. C 100 Required subcooling C 5 Condenser pinch C 1 Engine speed RPM 1,200 Engine power kw 125 Pump - 36% Optimization method: For Vapor pressure from 20 to 30 bara Calculate Massflow, with an evaporator pinch model Optimize expander design to maximize its mechanical power Calculate Fuel saving with a pump model Pick up best fuel saving and freeze expander design 24

25 Fuel benefit assessment Units Ethanol 96% r1233zd Cyclopentane Cyclopentane Recuperator - No Yes No Yes Cooling type - Indirect Direct Indirect Indirect Cooling temp. C Exp. outlet pressure bara Vapor power kw Exp. power EVE-T-new kw Pump power kw Fuel benefit % Front radiator size % Exhaust Evaporator size % Cost material SS, Cast iron, Coated aluminum Mostly Aluminum Aluminum ok? Aluminum ok? Cost - Fluid /kg ~1 ~20 ~2? ~2? 25

26 Conclusion Today, Performance is a key factor for demotrucks : Access to high cooling power at low temperature is critical Control algorithms with easy calibration but tomorrow TCO will be decisive to step into mass production : Proprietary working fluids are expensive Aluminum compatibility seems a key Safety issues To answer common requirements from OEMs & Tier1s, EXOES develops:. A flexfluid expander. A low speed expander (gear ratio of ~2). A robust expander that accepts droplets.a robust expander that accepts high transient conditions (0% OCR accepted in transient) We are looking for a partner to test our expander with cyclopentane 26

27 Inlet Pressure (bara) EXOÈS - RANKINE TECHNOLOGIES Effective Isentropic Efficiency [%] Fluid : EtOH 95.5% Outlet Pressure = 1 bara 56 Overheat = 30 C Speed (rpm) THANK YOU! REMI.DACCORD@EXOES.COM 27