A QUANTUM LEAP FOR HEAVY-DUTY TRUCK ENGINE EFFICIENCY – HYBRID POWER SYSTEM OF DIESEL AND WHR-ORC ENGINES
Gerhard Regner, Ho Teng and Chris Cowland AVL Powertrain Engineering, Inc.
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 1 WASTE HEAT RECOVERY FROM HEAVY-DUTY DIESEL TRUCK ENGINES
MOTIVATION
• Continuous increase in oil price • Continuous decrease in energy reserves
OBJECTIVE
• Improvement in overall efficiency of HD diesel truck engines by recovering high-energy-level waste heat
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 2 WASTE HEAT RECOVERY FROM HEAVY-DUTY DIESEL TRUCK ENGINES
CONTENT
• Energy levels of various sources of waste heat from a typical HD diesel truck engine
• Hybrid power system of diesel-cycle and WHR organic- fluid Rankine cycle
• Potential improvement for overall engine efficiency for HD diesel truck engines with WHR-ORC
• Summary
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 3 AN OUTLOOK OF WORLD FOSSIL FUEL RESERVES
• Proved reserves of fossil fuels:
oil : ∼ 161.9 × 109 tons
NG: ∼ 179.5 × 1012 m3
coal: ∼ 909.1 × 109 tons
• Reserves (R) to production (P) ratios:
(R/P)_oil : ∼ 41 yrs (world average basis)
(R/P)_NG: ∼ 67 yrs (world average basis)
(R/P)_coal: ∼ 164 yrs (world average basis)
Source: BP Statistical Review of World Energy, June 2005
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 4 IMPROVING ENGINE EFFICIENCY BY WASTE HEAT RECOVERY
• Options for transportation sector to deal with coming energy shortage problem are:
• Introduce alternative fuels, ideally, from relatively rich and long-lasting resources
• Improve efficiency of energy utilization
• HEV for passenger cars • WHR for heavy-duty trucks (Class 7-8)
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 5 WASTE HEAT FROM HEAVY-DUTY DIESEL ENGINES
Q& Note: In general, Q&EGR− cooler is an internal CAC energy flow. In the single- coolant-loop system, it Cooled charge air is combined with Q&coolant and rejected to ambient via the radiator; in the two-coolant-loop system, it is rejected via the secondary radiator. Charge air cooler (CAC)
Compressor Q&EGR− cooler
m& air hair EGR cooler Cooled EGR Sources of waste heat
Pcompressor m& exhhexh
m& ch arg ehch arge
Turbine & Sources of waste heat Qradiation
Q&oil _ turbo− lub rication
Q& m& fuel Hv coolant Q&c _ cylinder −head
Q&c _ water − jacket Radiator/oil-cooler
Ploss _ friction /Q & oil _lubrication
Q&oil _ piston−cooling PIndicated
Ploss _ misc/Q&dissipation
Ploss_fuel-pump
Pbrake
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 6 WASTE HEAT OF TRUCK DIESEL ENGINE AT FULL LOAD
ENERGY BALANCE OF A TYPICAL TRUCK DIESEL ENGINE
Brake power Exhaust_net Radiator CAC 45
40
35 ] % 30 y [ g
er 25 en - el
u 20 F y/ g
er 15 n E 10
5
0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Normalized engine speed [-]
Truck diesel-engine waste heat is about 58-62% fuel energy; up to 30% of the waste heat is with high energy level.
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 7 WASTE HEAT EVALUATION: ENERGY VS. EXERGY
• First law of thermodynamics
• Energy is evaluated by quantity.
• Second law of thermodynamics
• Energy = Exergy (useful work) + Anergy (equivalent to energy in ambient).
• Exergy is an evaluation of energy level of waste heat.
• Exergy of waste heat increases with its temperature.
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 8 TEMPERATURE LEVELS OF TYPICAL TRUCK DIESEL ENGINE WASTE HEAT AT FULL LOAD (W/O EGR)
WASTE-HEAT TEMPERATURES OF A TYPICAL TRUCK DIESEL ENGINE
T_exh_after-turbine T_CAC-in T_radiator-in 600
500
] 400 C e [ r u
at 300 er p em
T 200
100
0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Normalized engine speed [-]
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 9 EXHAUST TEMPERATURE FOR TYPICAL TRUCK DIESEL ENGINE
EXHAUST TEMPERATURE FOR A TYPICAL TRUCK DIESEL ENIGNE
Without EGR With EGR (estimated) 650
600
550
[C] 500 e n i b r 450 -tu e r
fo 400 e b _ h
x 350 e _ T 300
250
200 5 10 15 20 BMEP [bar]
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 10 EVALUATION OF WASTE HEAT BY ITS EXERGY VALUE
ENTHALPY AND EXERGY OF EXHAUST AT LAMBDA = 1.5 (Ambient temperature = 20 C)
Enthalpy Exergy Exergy/Enthalpy 1600 100
1440 90 g]
/k 1280 80 J k
Diesel exhaust ] [ 1120 70 % gy temperatures [ r e py
960 60 l x , e 800 50 ha nt lpy E /
ha 640 40 gy r nt e e x
480 30 E ic if c 320 20 pe S 160 10
0 0 20 220 420 620 820 1020 Te mperature [C]
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 11 ORGANIC RANKINE CYCLE FOR WASTE HEAT RECOVERY
Organic fluid Rankine cycle (ORC) for waste heat recovery:
Temperature Temperature range of waste heat
HT EGR cooler pH (Exhaust before turbine) Supercritical ORC
Sub-critical ORC Exhaust pipe LT EGR cooler Expansion process (turbine or expander)
CAC pL
Liquid region Two phase region Vapor region Entropy
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 12 WHR SYSTEM: TURBINE VS. EXPANDER
• Turbine and reciprocating Rankine engines
Working fluid Working fluid Turbine Expander
Heat source Heat source
Evaporator Heat rejection Evaporator Heat rejection
Condenser Condenser
Pump Pump
Turbine Rankine Engine Reciprocating Rankine Engine
• Expansion in a steam/vapor turbine is limited by the condensation temperature. • Expansion in a reciprocating engine is limited by the ambient pressure.
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 13 WHR SYSTEM: WORKING FLUIDS (1)
• Three types of working fluids: wet-fluid (e.g., water), isentropic fluid (e.g., R134a), and dry-fluid (e.g., R245fa)
THREE TYPES OF WORKING FLUIDS Water R134a R245fa 1.1
1.0 l [-] a ic it r c 0.9 T / e T
r 0.8 u at
er 0.7 emp t 0.6 ced u
ed 0.5 R
0.4 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
Relative entropy S/Sreference [-]
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 14 WHR SYSTEM: WORKING FLUIDS (2)
• Isentropic and dry fluids are appropriate working fluids for both turbine and reciprocating Rankine engines. • Ideal working fluid for given waste heat condition can be developed with a mixture of dry- and wet-type fluids.
Temperature Critical point
Mixture
Wet fluid
Dry fluid Entropy
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 15 HYBRID POWER SYSTEM OF DIESEL AND RANKINE ENGINES W/ LTC LOOP INTEGRATED IN RANKINE LOOP
ORC working fluid Coolant
Charge
Radiator Condenser Engine
Coolant pump
Expander Exhaust LP-Pump
EGR mixer
HT-EGR cooler LT-EGR cooler CAC
HP-Pump
Exhaust cooler Aftertreatment/DPF T C
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 16 WASTE HEAT RECOVERY: A CASE STUDY
Case study of a HD diesel engine at rated power, with a supercritical Rankine loop being integrated with the LTC loop:
Energy carriers Brake power Exhaust Radiator EGR CAC
Energy [kW] 275 391 166 78 55 Energy/Input-energy [%] 27.6 39.2 16.6 7.8 5.5 Exergy [kW] 275 109* ∼ 17 45* 15* Exergy/Energy [%] 100 28 ∼ 10 34 8
• Evaluated by enthalpy before energy transfer process 169 kW Simulation result: 29.5% recovery Power of the supercritical reciprocating Rankine engine ≈ 50 kW Power of the diesel-Rankine hybrid system = 325 kW Improvement in overall efficiency ≈ 18%
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 17 WASTE HEAT RECOVERY: APPLICATIONS
• Most attractive on-road-vehicle applications of WHR-ORC are heavy- duty diesel trucks for long distance hauling (Class 7-8).
• Supercritical WHR-ORC system may be more practical (the high-cost evaporator can be avoided).
• The WHR-ORC system can function as a LT-coolant loop for EGR and charge air cooling.
• The expander/turbine can be bypassed when waste heat level is too low – the Rankine loop reduces to a regular LT-coolant loop.
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 18 A QUANTUM LEAP FOR HD TRUCK ENGINE EFFICIENCY?
• If waste-heat temperatures > 400 °C, it is possible for the efficiency of the WHR Rankine engine to be 15 ∼ 20%.
• Cost comparison for 18% recovery case:
200,000 miles/yr / 6 mpg × $3.15/gal = $105,000/yr
$105,000/yr × 0.18 = $18,900/yr • With a diesel/Rankine hybrid power system, class 7-8 truck engines could possibly reach an overall efficiency up to
50% Quantum Leap
42% (current level)
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 19 THANK YOU FOR YOUR ATTENTION!
The 12th Diesel Engine-Efficiency and Emissions Research Conference, August 2006, Detroit, Michigan Page 20