Test on a CO2-Based Transcritical Power Cycle (CTPC)under Various Engine Conditions

Ligeng Li1, Hua Tian1, Lingfeng Shi1,2, Gequn Shu1,2

1 Tianjin University

2 University of Science and Technology of China

4. Summary

Outline

2. System and Method

3. Results

1. Background

Background

Energy Saving of Engine

In distributed generation In truckIn ship

high thermal efficiencyhigh energy density

Good fuel flexibility low costhigh reliability

Engine is widely used and plays an irreplaceable role in the market.

Consume >60% petroleum in China, 2017.

Results in 25% of CO2 emission, 2013

Energy saving of engine shows great significance.

31%

15%16%

13%

25%CO2 emission

Electric utilities

Construction industry

Commerce and live

other

Transportation

Background

Turbocharging

Thermoelectric generator

Power or Work

Thermodynamic cycle: High efficiency

Well thermal match

Good feasibility

Thermodynamic Cycle

WHR

Energy saving

WHR: most efficient way to improve engine efficiency

(engine coolant)

Background

Combined recovery of exhaust gas and engine coolant

Working Fluid

Exhaust Gas

Engine coolant

Preheater Gas Heater

Turbine

Condenser

Pump

g,ing,out

1 3

45

2

c,inc,out How to find a working fluidthat achieve highly combined recovery of exhaust gas and engine coolant？

Thermodynamic cycle

Background

Characteristic of exhaust gas and engine coolant

Engine Waste Heats (e.g. a 245 kW diesel engine)

Waste heats Temperature Recovery range State Quantity

Exhaust gas 500˚C 500˚C-120˚C Gas 100 kW

Engine coolant 90˚C 90˚C-70˚C Liquid 125 kW

Exhaust gas:high temperaturewide temperature range large quantity

Engine coolant：low temperaturenarrow temperature rangelarge quantity

Temperature (℃)Temperature (℃)

Background

Ideal working fluids

A1

A2

Ideal working fluid

Heated by engine coolant

Heated by exhaust gas

Ideal working fluid

CO2

A1:A2=Qc:Qg

CO2 is the closest to the ideal working fluid for highly combined recovery of exhaust gas and engine coolant.

Background

Utilization rate of engine coolant

Note：all utilization rate of exhaust gas >90%

30 60 90 120 150 180 2100

20

40

60

80

100

R123

Utilization rate of engine coolant (%)

butaneR22

propylene

R143a

CO2

P3=1.5P

cri t

3=300℃ U

tiliz

atio

n r

ate

of e

ng

ine

co

ola

nt（

%）

Critical temperautre (℃)

CO2:

the highest utilization rate of

engine coolant

Besides, CO2 is also an environmental working fluid and has miniaturization

capacity due to its superior heat transfer and flowing property.

Objective of this study

CO2-based Transcritical Power Cycle (CTPC) with preheating process:

Preheating process by engine coolant could improve 60% Wnet

------ the test result in 2017, presented in ORC2017

Under constant engine condition

How about the performance under various engine condition？

Heat of exhaust gas under various engine condition

Heat of engine coolant under various engine condition

Parameters of exhaust gasunder road conditions

4. Summary

Outline

2. System and Method

3. Results

1. Background

System

Expansion Valve

PT

PTPT

T T

Diesel Engine

Gas Heater

Regenrator

PrecoolerCondenserCO2 TankFilter

CO2 Flowmeter

CO2 Pump

Damper

Refrigeration Unit

Preheater

PT PT

PT

T P

PT

PT

T

T

PT

PTT & P Sensor

T Display

P Display

ValveCooling Water

Exhaust Gas

Engine Coolant (EC)

CO2

T

EC Flowmeter1

EC Tank

EC Pump1

EC Pump2

Cooling Water Flowmeter

Cooling Jacket

1 2 3

456

7

9

c,1 c,2

g,1

ec,1

ec,2

ec,3

ec,4

c,3

g,2

g,0 PT

Valve1 Valve2

Valve3 Valve4

EC Flowmeter2

Cold EC Supplement

Valve5

Valve6

8T P

PT

PT

Main design parameters：

Power output：4.5kW Maximum pressure : 11MPa Maximum temperature : 230℃

Diesel engine

system

Engine coolant

system

CTPC system

Cooling water

system

SystemCTPC system

Control, Record and Alarm

PumpGas heater

The other HEs Expansion Valve/ Turbine

Experiment strategy

Starting Stopping or idling Random process

From 1100rpm/601N.m

sudden idling

sudden stopping

Engine speed

Engine torque

Observe pressure, temperature and heat quantity in preheater and gas heater

Three dynamic change process of engine

4. Summary

Outline

2. System and Method

3. Results

1. Background

Results Starting process of engine

Add preheating

Starting process

Step ascension of CO2 temperature

Improve output

Step ascension of liquid height

Keep more liquid in the tank

Step ascension of CO2 pressure

Results

Heat from exhaust gas（25.4~34.9 kW）

Heat from engine coolant（19.5~22.8 kW）

• Preheating quantity is stable and keep output capacity under random process.

• Analysis: engine coolant has large specific heat capacity

Random process

Random process of engine

Results

Idling or stopping process of engine

Idling or stopping process

When sudden stopping:• with preheating：273s• without preheating: 127s

Effective time to output

When sudden idling:• with preheating：739s• without preheating: 278s

With preheating:More than double time

Stopping without preheating：Sudden rise of expansion inlet pressure

Results

Reason analysis on the phenomenon of sudden rise

expansion outlet pressure

Idling or stopping process

Concave-shaped change

Heating intensity ↓

Expansion inlet pressure ↓

Expansion outlet pressure

firstly ↓, then ↑ limited by condensation condition

sudden rise of expansion inlet pressure

4. Summary

Outline

2. System and Method

3. Results

1. Background

Results

• When adding preheating process, the CTPC would appearstep ascension of CO2 pressure and CO2 temperature.1 Efficient

Preheating process achieve benefits during dynamic operation under various engine condition:

• Preheating quantity is stable (19.5~22.8 kW) under randomprocess of engine.

• Extent more than double time to keep output capacityunder stopping or idling of engine.

2 Stable

• Avoid sudden rise of expansion inlet pressure understopping of engine.3 Safe

Acknowledgements:

• State Key Program of National Natural Science Foundation of China (No. 51636005)

Email: slf@ustc.edu.cn