Modelling waste heat recovery with a turbogenerator on a ... - Ricardo

<strong>Modelling</strong> <strong>waste</strong> <strong>heat</strong> <strong>recovery</strong> <strong>with</strong> a
<strong>turbogenerator</strong> on a diesel engine
A presentation to the Ricardo European User Conference
Ian Briggs
Queen’s University Belfast
Geoff McCullough
Stephen Spence
Roy Douglas
Richard O’Shaughnessy Queen’s University Belfast
27 th March 2012
Alister Hanna
Cedric Rouaud
Rachel Seaman
Wrightbus Ltd.
Ricardo Ltd.
Revolve Technologies Ltd.
© 2012, The Queen’s University of Belfast

Acknowledgement
• The authors would like to acknowledge the UK Technology Strategy
Board and Invest Northern Ireland for the financial support in the
Project ‘TERS – Thermal Energy Recovery Systems’
• Also, Wrightbus, Revolve and Ricardo for their technical contributions
© 2012, The Queen’s University of Belfast
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Contents
• Introduction
– Project Background
– Overview
• Waste Heat Recovery Project
– Engine <strong>Modelling</strong>
– Waste <strong>heat</strong> <strong>recovery</strong> modelling
• Results
• Optimisation
• Conclusions
• Future Work
© 2012, The Queen’s University of Belfast
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Introduction
• Background
– Project funded by Technology Strategy Board / Invest Northern Ireland
– Collaboration between three commercial partners (Wrightbus Ltd, Ricardo Ltd
and Revolve Technologies Ltd) and three post-graduate students at QUB
– Researching thermal management of a Wrightbus hybrid bus
• Project Aims & Objectives
– Work in conjunction <strong>with</strong> the group members to reduce fuel consumption on
Wrightbus’ hybrid bus
– Collectively, we aim to achieve 10% reduction in fuel consumption using
turbocompounding and Rankine cycles on exhaust line and cooling circuit
– Apply turbocompounding to the hybrid bus engine to recover <strong>waste</strong>d energy
and reduce fuel consumption (via the creation of a computational model)
© 2012, The Queen’s University of Belfast
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Waste Heat Recovery
• These factors have driven the aims of this project
• These problems may be addressed by recovering <strong>waste</strong>d <strong>heat</strong> from an
Internal Combustion Engine
• Approx. 30% of fuel energy is <strong>waste</strong>d through the exhaust
– Offers a large potential to recover energy
• Even a small reduction in <strong>waste</strong> <strong>heat</strong> can
lead to significant improvements in
fuel consumption
© 2012, The Queen’s University of Belfast
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Turbocompounding
• Three main forms of turbocompounding:
Mechanical Turbocompound
• Uses a Power Turbine to
extract energy from
exhaust gas
• Large, heavy system
• Complex operation
• Limited methods of using
the generated power
Figure adapted from: C. Vuk, "Turbo Compounding: A Technology Who's Time Has Come", Proc. 11th Diesel Engine Emissions Reduction
(DEER) Conf., Chicago, USA, 2005.
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Turbocompounding
• Three main forms of turbocompounding:
Electric Turbocharger
• Small motor/generator
mounted on the
turbocharger shaft
• Very small package
• Can be used to generate
power or to help spin the
turbocharger
• Requires a redesign of the
existing turbocharger
Figure adapted from: F. Gerke, “Diesel Engine Waste Heat Recovery Utilizing Electric Turbocompound Technology”, Proc. 7th Diesel Engine
Emissions Reduction (DEER) Workshop, Portsmouth, USA, 2001.
© 2012, The Queen’s University of Belfast
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Turbocompounding
• Three main forms of turbocompounding:
Turbogenerator
• Power turbine connected
to a small generator
• Mounted downstream of
the turbocharger turbine
• Small package, light
weight
• Ideally suited to the hybrid
bus application
Figure adapted from: Green Car Congress, CPT Brings TIGERS Technology to VIPER Project for Enhanced Energy Recovery. [Online]. Available:
http://www.greencarcongress.com/2010/09/cpt-20100923.html [Accessed: 2 Nov 2010]
© 2012, The Queen’s University of Belfast
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Turbocompounding
Fuel Energy
Power Generated
Turbogenerator
Compressed Air
Turbocharger
Intake Air
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<strong>Modelling</strong> Strategy
Obtain Geometry
Measurements from Engine
Create baseline engine model
using WAVE
Validate baseline engine model
against experimental data
Activate <strong>turbogenerator</strong> in
Engine Model
Assess effect of <strong>heat</strong> <strong>recovery</strong>
on fuel consumption
Optimise the <strong>turbogenerator</strong>
Optimise the engine package
© 2012, The Queen’s University of Belfast
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Engine Model Construction
EGR Valve
• Engine Model (WAVE)
PID 3
EGR Cooler
PID 1
Turbogenerator
Turbine
Turbocharger
Turbine
Exhaust Aftertreatment
Turbocharger
Compressor
Inlet Manifold
Exhaust Ports &
Intake Ports Manifold
Fuel Injectors Engine
Air Filter Block
PID 2
© 2012, The Queen’s University of Belfast
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Baseline Model Validation
• Baseline model validation
– The model has been validated
across the full operating range of
test data
– Error is less than 2% over the
majority of the operating range
– Particularly at the four most
frequently accessed points of
drive cycle (Pts 1-4)
• Thus, we have confidence in the
model’s ability to predict the
current engine performance
© 2012, The Queen’s University of Belfast
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Turbogenerator Model
• Initial runs simply ‘switched on’ the <strong>turbogenerator</strong>
Power Turbine
Bypass Valve
• Bypass Valve open = Baseline Configuration
• Bypass Valve Closed = Turbogenerator Activated
© 2012, The Queen’s University of Belfast
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Turbogenerator Model
• Using a generic scaled turbine performance
map for values of:
– Pressure Ratio
– Mass Flow
– Shaft Speed
– Efficiency
• Using the four commonly accessed
points (Pts 1-4) plus one other midload
point (Pt 5)
• Matched AFR and torque
– Manual process for each case by adjusting gain on PID controllers
• Initial turbine map created a peak power output of 4.6kW on the
<strong>turbogenerator</strong> at full engine load
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Turbogenerator Model Results
• 4.6kW Power turbine results:
Operating Point P TG (kW) Δ BSFC
Pt 1 0.01 -0.12%
Pt 2 0.31 -1.03%
Pt 3 1.66 -1.55%
Pt 4 4.57 -2.37%
Pt 5 3.46 -1.24%
• Peak reduction in BSFC of almost 2.4%
• Represents a modest improvement in fuel consumption
• Turbine map was then scaled to investigate the effects of a more powerful
device:
• Four other devices created (up to 11.5kW)
• Shaft speed limited to 80,000rpm
© 2012, The Queen’s University of Belfast
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Turbogenerator Model Results
• 9.2kW device represents a peak BSFC improvement of 4.4%
• A larger device continues to improve BSFC performance at other load
points
• Highlights the difficulty in choosing a device for off-design conditions
• These results involve no turbocharger matching (due to cost reasons)
© 2012, The Queen’s University of Belfast
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Energy Audit
• To understand the results, an energy audit was performed for the engine
• This looks at the main losses in the engine, via the distribution of fuel
energy supplied:
– Brake Work;
– Pumping Work;
– Heat Transfer through the cylinder walls;
– Wasted <strong>heat</strong> in the exhaust gas;
– Energy lost to friction;
– Energy lost due to combustion inefficiency.
• Results are presented for one operating point (Pt 5):
© 2012, The Queen’s University of Belfast
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Energy Audit
• Brake Work, Friction Work and
Combustion Efficiency are all
approximately constant
– Same torque demand
– Friction is largely governed by
speed and load
• Slightly less <strong>heat</strong> transfer in the
<strong>turbogenerator</strong> models
– Differences in peak cylinder
temperature between models
• Increased <strong>heat</strong> in exhaust gas
– Higher exhaust temperature
caused by presence of
<strong>turbogenerator</strong>
• Pumping work increases from
125J/cyc to 562J/cyc
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Energy Audit
Pumping Work
Pexh ≈ 4.4 bar
Pexh ≈ 2.3 bar
• Higher peak cylinder pressure
– To maintain same BMEP despite
higher exhaust pressure
• Higher pressure on the exhaust
stroke of <strong>turbogenerator</strong> model
– Clearly highlights the backpressure
caused by the <strong>turbogenerator</strong>
• Larger area enclosed <strong>with</strong>in the
pumping loop of the <strong>turbogenerator</strong>
model
– Integrates to give higher pumping
work
• These plots confirm our
understanding of the <strong>turbogenerator</strong>
operation
© 2012, The Queen’s University of Belfast
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Conclusions
• Turbogenerator has been selected to model <strong>waste</strong> <strong>heat</strong> <strong>recovery</strong> on a
diesel-electric hybrid bus
– Small packaging requirements
– Low weight
– Ease of integration into existing on-board batteries
• The 2.4-litre diesel engine used in the hybrid bus has been modelled
using WAVE
– The engine model has been validated across its full operating range
– Error between simulated and measured results is generally less than 2%
• A scaled generic turbine map was used to install a <strong>turbogenerator</strong> in the
engine model
© 2012, The Queen’s University of Belfast
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Conclusions
• Results for the <strong>turbogenerator</strong> have been produced at five key operating
points
– An initial 4.5kW device produces a 2.4% improvement in BSFC at full engine
load <strong>with</strong> no turbocharger matching
– A higher-power (9kW) device produces 4.3% improvement in BSFC <strong>with</strong> no
turbocharger matching
• Increasing the power output of the <strong>turbogenerator</strong> reduces this peak
BSFC improvement
– Effect of backpressure is a critical consideration to the success of the system
• This theoretical study has shown the <strong>turbogenerator</strong> can provide a
reduction in fuel consumption on the engine used in this project
© 2012, The Queen’s University of Belfast
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Future Work
• Begin detailed optimisation of the <strong>turbogenerator</strong> model
– Suggest the optimum configuration required for our application
– Examine off-design performance
– Examine engine parameters such as valve timing
• Examine and validate the <strong>turbogenerator</strong> turbine maps used in this work
• Begin re-sizing the existing turbomachinery to optimise the total system
• Examine the effects of <strong>heat</strong> <strong>recovery</strong> on a hybrid bus drive cycle
– QUB-developed model that includes data of road gradient, vehicle speed and
acceleration and auxiliary loads
– Engine model output can be used to analyse <strong>heat</strong> <strong>recovery</strong> on a virtual bus drive
cycle
• Investigate effects of combined results <strong>with</strong> Rankine systems
© 2012, The Queen’s University of Belfast
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Thank you…any questions?
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