waste heat recovery from internal combustion engines (ice)

Waste Heat Recovery from Internal Combustion Engines (ICE) Sandhya Thantla [email protected] KTH CCGEX Waste heat recovery (WHR) from the automotive engines is the need of the hour to improve overall engine efficiency, reduce fuel consumption and global warming. The Rankine cycle (RC) system is applied to recover unused heat from the engines for conversion into useful power. For an effective system integration (WHR + engine), it is necessary to identify the factors influencing the performance of the heat recovery system including the thermodynamic cycle, working fluid and the components such as heat exchangers and expansion devices. The aim of this project is to design and develop an effective Rankine cycle system to recover unused potential heat from the Automotive ICEs with the most suitable expansion machines. Introduction and Motivation: Globally, the Rankine cycle system has proven to be very effective in converting unused heat into useful power. The choice of the working fluid determines the cycle and its boundary conditions. As the expansion machine is responsible for converting heat into useful power output, its choice and efficiency are the crucial factors as well. Since automotive ICE WHR involves low-to-moderate quality of heat, it is necessary to look into more types of expanders for the application besides the piston and the turbine expanders. In this work, basic Rankine cycle calculations are made for a selected engine operating point to determine the limits on the evaporating temperatures and pressures for a desired power output. A preliminary sensitivity analysis is performed to identify the parameters affecting the expander’s power output, its design and efficiency. ENGINE ENERGY ANALYSIS - SCANIA DL6 12.7L HEAVY DUTY DIESEL Heat source: Exhaust gas Exhaust gas ΔT: 301 C Total heat available from the heat source: 47 kW INPUT PARAMETERS FOR THE RANKINE CYLE SYSTEM Working fluid: Water Condensing pressure: 1.03 bar Ambient temperature: 30 C Vapour quality - After expansion : 1; After condensation : 0 Expected power output = Ranging from 1 kW to 4 kW CONDITIONS FOR SENSITIVITY ANALYSIS a. Reduced pressure ratio at constant mass flow rate b. Reduced mass flow rate at constant pressure ratio (Comparison performed for the range of power outputs assuming fixed heat source conditions ) Results: SUMMARY SENSITIVITY OF WORK OUTPUT Effect of Mass flow rate is higher at power outputs above 2.5 kW Effect of Pressure ratio (PR) is higher for lower power outputs (1- 2.5 kW) CONCLUSION Higher mass flow rates - Increased heat input into the system - Improved power output Fluids with higher mass flow rates may be more effective at a limited PR PR analysis may help in the choice of expanders and their sizes Pinch point difference has to be included for better predictions 1-2 Expansion 2-3 Condensation 3- 4 Pumping 4-5 Preheating 5-1 Vaporisation 0,0 1,1 2,2 3,3 4,4 5,5 6,6 7,7 8,8 50 100 150 200 250 300 350 s [kJ/kg-K] T [°C] 425 kPa 150 kPa Water 1 2 3 4 5 Power output = 2.5 kW Amb. Temp. = 30 C 0,00 5,00 10,00 15,00 20,00 25,00 30,00 35,00 % of reduction Reduction in Power output (kW) PARAMETRIC EFFECTS ON THE POWER OUTPUT reduction in pressure ratio reduction in mass flow rate 4 kW to 2.5 kW 2.5 kW to 1 kW Acknowledgement: 1. Professor Anders C Erlandsson, ICE Division/KTH 2. Jens Fridh, PhD, Energy technology/KTH 3. Industrial partners Fig.1: Preliminary Rankine cycle design for the available heat source and fixed boundary conditions Fig.2: Sensitivity of the power output with reduction in mass flow rates and pressure ratios

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Waste Heat Recovery from Internal Combustion Engines (ICE)

Sandhya Thantla

[email protected] KTH CCGEX

Waste heat recovery (WHR) from the automotive engines is the need of the hour to improve overall engine efficiency, reduce fuel consumption and global warming. The Rankine cycle (RC) system is applied to recover unused heat from the engines for conversion into useful power. For an effective system integration (WHR + engine), it is necessary to identify the factors influencing the performance of the heat recovery system including the thermodynamic cycle, working fluid and the components such as heat exchangers and expansion devices. The aim of this project is to design and develop an effective Rankine cycle system to recover unused potential heat from the Automotive ICEs with the most suitable expansion machines.

Introduction and Motivation:

Globally, the Rankine cycle system has proven to be very effective in converting unused heat into useful power. The choice of the working fluid determines the cycle and its boundary conditions. As the expansion machine is responsible for converting heat into useful power output, its choice and efficiency are the crucial factors as well. Since automotive ICE WHR involves low-to-moderate quality of heat, it is necessary to look into more types of expanders for the application besides the piston and the turbine expanders. In this work, basic Rankine cycle calculations are made for a selected engine operating point to determine the limits on the evaporating temperatures and pressures for a desired power output. A preliminary sensitivity analysis is performed to identify the parameters affecting the expander’s power output, its design and efficiency.

ENGINE ENERGY ANALYSIS - SCANIA DL6 12.7L HEAVY DUTY DIESEL

Heat source: Exhaust gas

Exhaust gas ΔT: 301 C

Total heat available from the heat source: 47 kW

INPUT PARAMETERS FOR THE RANKINE CYLE SYSTEM

Working fluid: Water

Condensing pressure: 1.03 bar

Ambient temperature: 30 C

Vapour quality - After expansion : 1; After condensation : 0

Expected power output = Ranging from 1 kW to 4 kW

CONDITIONS FOR SENSITIVITY ANALYSIS

a. Reduced pressure ratio at constant mass flow rate

b. Reduced mass flow rate at constant pressure ratio

(Comparison performed for the range of power outputs assuming fixed heat source conditions )

Results:

SUMMARY SENSITIVITY OF WORK OUTPUT Effect of Mass flow rate is higher at power outputs above 2.5 kW Effect of Pressure ratio (PR) is higher for lower power outputs (1- 2.5 kW) CONCLUSION Higher mass flow rates - Increased heat input into the system - Improved

power output Fluids with higher mass flow rates may be more effective at a limited PR PR analysis may help in the choice of expanders and their sizes Pinch point difference has to be included for better predictions

1-2 Expansion 2-3 Condensation 3- 4 Pumping 4-5 Preheating 5-1 Vaporisation

0,0 1,1 2,2 3,3 4,4 5,5 6,6 7,7 8,8

100

150

200

250

300

350

s [kJ/kg-K]

T [

°C]

425 kPa