presentation sae 2010-01-1511
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Prof. PhD Victor Gheorghiu Hamburg University of Applied Sciences, Germany
CO2-EMISSION REDUCTION BY MEANS OF ENHANCING THE THERMAL CONVERSION
EFFICIENCY OF ICE CYCLES
SAE 2010-01-1511
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CONTENT
Introduction, Thermodynamic Ways for improving the TCE and their Restrictions
Goals of this Investigation
Analysis of classical Atk inson Cycle Implementation to aspirated and turbocharged engines
New Solution for Atk inson Cycle Implementation while Meeting usual Thermal & Mechanical Restrictions and their Analysis For Aspirated Engines
For Very High Pressure Turbocharged Engines
Ideal V,p,T-Model for easier comparison of the thermal Cycle of Turbocharged Engines at Full and Part Loads
Conclusion
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INTRODUCTION Thermodynamic Ways for improving the TCE* of ICE cycles:
Ways 1. Increasing effective compression
ratio 2. Shorten eff. compression stroke
(e.g. delaying intake valve closing) 3. Completing eff. expansion stroke
(e.g. delaying exh. valve opening) 4. Turbo-charging for a concurrent
increase in TCE & BMEP
Schematic Pressure-Volume diagram of a four stroke Seiliger cycle, where the Heat Release is modeled by constant Volume (2-3v), Pressure (3v-3p) and Temperature (3p-3). For this reason this Ideal Cycle will be referred here as Seiliger V,p,T-cycle.
* TCE = Thermal Conversion Efficiency
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Ways 1. Increasing effective Volumetric
Compression Ratio (VCR) 2. Shorten eff. compression stroke
(e.g. delaying intake valve closing) 3. Completing eff. expansion stroke
(e.g. delaying exh. valve opening) 4. Turbo-charging for a concurrent
increase in TCE & BMEP
Thermodynamic Ways for improving the TCE of ICE cycles:
1.
INTRODUCTION
Schematic Pressure-Volume diagram of a four stroke Seiliger cycle, where the Heat Release is modeled by constant Volume (2-3v), Pressure (3v-3p) and Temperature (3p-3). For this reason this Ideal Cycle can be referred as Seiliger V,p,T-cycle.
* TCE = Thermal Conversion Efficiency
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Schematic Pressure-Volume diagram of a four stroke Seiliger cycle, where the Heat Release is modeled by constant Volume (2-3v), Pressure (3v-3p) and Temperature (3p-3). For this reason this Ideal Cycle can be referred as Seiliger V,p,T-cycle.
INTRODUCTION
Ways 1. Increasing effective volumetric
compression ratio 2. Shorten eff. compression stroke
(e.g. delaying intake valve closing) 3. Completing eff. expansion stroke
(e.g. delaying exh. valve opening) 4. Turbo-charging for a concurrent
increase in TCE & BMEP
Thermodynamic Ways for improving the TCE of ICE cycles:
2.
1.
* TCE = Thermal Conversion Efficiency
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Schematic Pressure-Volume diagram of a four stroke Seiliger cycle, where the Heat Release is modeled by constant Volume (2-3v), Pressure (3v-3p) and Temperature (3p-3). For this reason this Ideal Cycle can be referred as Seiliger V,p,T-cycle.
INTRODUCTION
Ways 1. Increasing effective volumetric
compression ratio 2. Shorten eff. compression stroke
(e.g. delaying intake valve closing) 3. Completing eff. expansion stroke
(e.g. delaying exh. valve opening) 4. Turbo-charging for a concurrent
increase in TCE & BMEP
Thermodynamic Ways for improving the TCE of ICE cycles:
3.
* TCE = Thermal Conversion Efficiency
2.
1.
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Schematic Pressure-Volume diagram of a four stroke Seiliger cycle, where the Heat Release is modeled by constant Volume (2-3v), Pressure (3v-3p) and Temperature (3p-3). For this reason this Ideal Cycle can be referred as Seiliger V,p,T-cycle.
3.
2.
1.
INTRODUCTION
Ways 1. Increasing effective volumetric
compression ratio 2. Shorten eff. compression stroke
(e.g. delaying intake valve closing) 3. Completing eff. expansion stroke
(e.g. delaying exh. valve opening) 4. Turbo-charging for a concurrent
increase in TCE & BMEP**
Thermodynamic Ways for improving the TCE* of ICE cycles:
4.
* TCE = Thermal Conversion Efficiency ** BMEP = Brake Mean Effective Pressure
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INTRODUCTION
Ways 1. Increasing effective
volumetric compression ratio 2. Shorten effective
compression stroke 3. Completing effective
expansion stroke 4. Turbo-charging for a
concurrent increase in TCE & BMEP
Conclusion: The four well-known Thermodynamic Ways for improving the TCE* cycles lead (for both aspirated & turbocharged engines) from Seiliger to Atkinson cycle!
Schematic Pressure-Volume diagrams of classical four stroke Seiliger (left) and Atkinson V,p,T-cycles
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Thermodynamic Ways for improving the TCE of ICE cycles and Consequences & Restrictions on their Implementation:
INTRODUCTION
Thermodynamic Ways 1. Increasing effective compression
ratio 2. Shorten effective compression
stroke 3. Completing effective expansion
stroke 4. Turbo-charging for a concurrent
increase in TCE & BMEP
Consequences & Restrictions Exceeding allowed pmax , Tmax , NOx (Diesel & SI), knocking (SI) etc. Decreased aspirated gas mass lower BMEP and lower TCE improvement Large displacement of the engine , heavy engine, lower TCE improvement Exceeding allowed pmax , Tmax , NOx (Diesel & SI), knocking (SI) etc.
* TCE = Thermal Conversion Efficiency ** BMEP = Brake Mean Effective Pressure
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Goals of these Investigations 1. Goal of this investigation is to analyze how much Thermal
Conversion Efficiency Potential have the known Implementations of the Atkinson cycle for: a) Aspirated and b) Supercharged Engines
2. Goal is the attempt to improve these Implementations in accordance with the previous presented Restrictions without prejudice the Thermal Conversion Efficiency (TCE) of the Atkinson cycle for: a) Aspirated and b) Supercharged Engines at Full and Part Loads
New Solutions for Atkinson Cycle
Implementation are needed!
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These simulations are doing here: For aspirated engine cycles with a self developed simulation tool For super-charged engine cycles with:
1. self developed Ideal V,p,T-Model for Seiliger and Atkinson cycles 2. AVL BOOST and for Validation of Ideal V,p,T-Model
Ideal V,p,T-Model is required here because: usual simulation tools have several influence parameters, analysis of their influence upon TCE is complicated and time expensive optimal combinations of these parameter which maximize TCE and
fulfill the above restrictions are very difficult to obtain.
o In all of here presented simulations entire cycle - including the gas exchange processes - are considered.
o To Enable the comparison of simulation results performed with Ideal V,p,T-Model and AVL BOOST, and for Eliminating the influence of Heat Exchange between different Simulation Variants, which is quite difficult to compensate, the Cylinder is treated here as an Adiabatic System.
Analysis Tools Presentation
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Aspirated Engines - Analysis of Toyota Implementation of the Atkinson Cycle in Prius II characterized by:
Source: Toyota
Atkinson cycle
Delaying
a) Shorten of the Effective Compression Stroke by means of Delaying of the Intake Valve Closing & b) Enhancing of the Volumetric Compression Ratio (VCR)
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Source: Toyota
Delaying
The questions are: 1. Is this Atkinson cycle
implementation optimal?
2. If not, why?
Atkinson cycle
Aspirated Engines - Analysis of Toyota Implementation of the Atkinson Cycle in Prius II characterized by:
a) Shorten of the Effective Compression Stroke by means of Delaying of the Intake Valve Closing & b) Enhancing of the Volumetric Compression Ratio (VCR)
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log(Pressure) - Volume diagrams for 1V and 2V related to SV
SV = Standard Variant (classical Cycle for Aspirated Engines, Seiliger Cycle) 1V = SV + 100°CA Delayed Intake Valve Closing 2V = 1V + 90% Increased Volumetric Compression Ratio (VCR) ~ Toyota Implementation of the Atkinson Cycle in Prius II Note: AFR is kept in all these variants identical!
intake valve closing in SV
eo = exhaust open ec = exhaust close io = intake open ic = intake close
intake valve closing in 1V
Increased VCR in 2V
intake valve closing in 1V & 2V
Simulation of this kind of Atkinson Cycle Implementation
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Indicated Fuel Conversion Efficiency – Crank Angle diagram
Pushing out of burned gases consumes more piston work in 1V as in SV because of lower pressure at exhaust valve opening & consequently of sluggish cylinder emptying
log(Pressure) - Volume diagram
Note: Toyota uses an SI aspirated engine in its Prius II which tries to achieve high efficiency by using an Atkinson cycle, where the intake valve is kept open for a large part of the compression stroke and the volumetric compression ratio (VCR) is enhanced
SV & 1V
eo = exhaust open ec = exhaust close io = intake open ic = intake close
intake valve closing in 1V
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Indicated Fuel Conversion Efficiency – Crank Angle diagram
The forth and back flow through the intake valve in 1V causes the most important losses referred to SV in the indicated fuel conversion efficiency
Fluid Mass - Volume diagram
SV & 1V
In 1V remains 46% less mass as
in SV in cylinder after scavenging
Pushing out of burned gases consumes more piston work in 1V as in SV because of lower pressure at exhaust valve opening & consequently of sluggish cylinder emptying
intake valve closing in 1V
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Indicated Fuel Conversion Efficiency – Crank Angle diagram
The forth and back flow through the intake valve in 1V causes the most important losses referred to SV in the indicated fuel conversion efficiency
Fluid Mass - Volume diagram
SV & 1V & 2V
Pushing out of burned gases consumes more piston work in 1V as in SV because of lower pressure at exhaust valve opening & consequently of sluggish cylinder emptying
Only the increasing with 90% of volumetric compression ratio in 2V restores the value of indicated fuel conversion efficiency referred to SV
intake valve closing in 1V & 2V
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In the case of aspirated engines, where the intake valve is kept open for a large part of the compression, the advantage of performing the cycle using this Atkinson implementation is of little benefit for following reasons: The Gain in Indicated Fuel Conversion Efficiency is modest and is largely dependent on the fine tuning of all parameters
The Pushing out of the burned gases consumed more piston work as in SV
The forth and back flow through intake valve causes the most important losses in the Indicated Fuel Conversion Efficiency (IFCE).
The specific power of the engine (or BMEP) is low because of the decreased retained mass of fresh charge in cylinder before combustion. As consequence a relatively large displacement and therefore heavy engine is needed to power the vehicle.
The Supercharging seem to be the necessary solution to compensate the diminishing of BMEP and for enhancing of Indicated Fuel Conversion Efficiency.
Conclusion referred to this Implementation of the Atkinson Cycle at Aspirated Engines
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Turbocharged (TC) Engines Analysis of classical Atkinson Cycle Implementations
characterized by:
a) Shorten of the Effective Compression Stroke, b) Enhancing of the Volumetric Compression Ratio c) Enhancing of the Boost Pressure + intensive Intercooling
SV-TC = Standard Variant (classical Cycle for Turbocharged Engines) 1V-TC = SV-TC + Delayed Suction 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR The Boost Pressure Level is chosen to meat the following Restrictions:
Without exceeding maximal Pressure on Cycle set here to ca. 210 bar Without exceeding maximal Temperature set here to ca. 2100 K Note: AFR cannot be kept more in all these variants identical!
Simulation of classical Atkinson Cycle Implementations in the following Variants:
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Turbocharged Engines Simulation of classical Atkinson Cycle
Implementations in the following Variants:
Pressure - Volume diagram IFCE – Crank Angle diagram
SV-TC & 1V-TC
Delayed Suction in 1V-TC
Very Delayed Suction in 2V-TC
SV-TC = Standard Variant (classical Cycle for Turbocharged Engines) 1V-TC = SV-TC + Delayed Suction + Increased Boost Pressure 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR + Very High Boost Pressure
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Turbocharged Engines Simulation of classical Atkinson Cycle
Implementations in the following Variants:
Pressure - Volume diagram IFCE – Crank Angle diagram
SV-TC & 1V-TC
Maximal Pressure on the cycle are nearly the same in all variants
Delayed Suction in 1V-TC
Very Delayed Suction in 2V-TC
SV-TC = Standard Variant (classical Cycle for Turbocharged Engines) 1V-TC = SV-TC + Delayed Suction + Increased Boost Pressure 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR + Very High Boost Pressure
eo = exhaust open ec = exhaust close io = intake open ic = intake close
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Turbocharged Engines / Classical Atkinson Cycle Implementations SV-TC = Standard Variant 1V-TC = SV-TC + Delayed Suction + Increased Boost Pressure 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR + Very High Boost Pressure
log(Pressure) - Volume diagram IFCE – Crank Angle diagram
SV-TC & 1V-TC
VCR
AFR
IMEP
pC , TC
eo = exhaust open ec = exhaust close io = intake open ic = intake close
IFCE
Piston Work for Scavenging is very different
Delayed Suction in 1V-TC
Very Delayed Suction in 2V-TC
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Temperature - Volume diagram IFCE – Crank Angle diagram
SV-TC & 1V-TC
Maximal Temperature on the cycle are nearly the same!
Turbocharged Engines / Classical Atkinson Cycle Implementations SV-TC = Standard Variant 1V-TC = SV-TC + Delayed Suction + Increased Boost Pressure 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR + Very High Boost Pressure
VCR
AFR
IMEP
pC , TC
IFCE
eo = exhaust open ec = exhaust close io = intake open ic = intake close
Return
Turbocharged Engines / Classical Atkinson Cycle Implementations SV-TC = Standard Variant 1V-TC = SV-TC + Delayed Suction + Increased Boost Pressure 2V-TC = 1V-TC + Very Delayed Suction + Increased VCR + Very High Boost Pressure
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Fluid Mass - Volume diagram IFCE – Crank Angle diagram
SV-TC & 1V-TC
Flowing back into the intake pipe
lower retained
Fluid Mass
VCR
AFR
IMEP
pC , TC
IFCE
Although the boost pressure is very different, IMEP and IFCE are virtually the same
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In 1V-TC (= SV-TC + Delayed Suction) although the boost pressure is 40% higher, TCE and IMEP are 6% less than in the SV-TC (standard version of the Seiliger cycle). For these reasons, an other approach is needed to implement the Atkinson cycle with a normal crankshaft drive. In 2V-TC (= 1V-TC + Very Delayed Suction + Increased VCR + very high boost pressure) the retained fresh charge mass into cylinder is much lower as in the SV-TC. Although the boost pressure in 2V-TC is more than five times higher at virtually the same IMEP, only a minor improvement of the TCE can be detected. This improvement can be expected to be somewhat better if AFR is kept identical in both cycles.
For this reason, the implementation of the Atkinson cycle by means of a significant delay of the suction and a strong enhancement of the charge pressure applied to an engine with classical crank mechanism does not represent a suitable solution.
Therefore, a new approach is needed to implement a real Atkinson cycle.
Conclusion referred to these Implementations of the Atkinson Cycle at Supercharged Engines
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The aim here is merely to estimate what potential for increasing the Indicated Fuel Conversion Efficiency (IFCE or TCE) exists when: For aspirated engines
The losses caused by the suction and partial expulsion of the fresh charge are eliminated (Variant 3V)
For turbocharged engines
Very high boost pressure + intensive intercooling turbocharging is implemented without reducing of aspirated mass & BMEP and with respect of the upper limits for pressure and temperature on the cycle (Variant 3V-TC).
For this reason asymmetrical crankshaft drives are here introduced which have shortened compression and extended expansion strokes.
In this way the piston work for compression is strongly diminished and the full potential of the very high boost pressure turbocharging can be used.
New Solutions for Atkinson Cycle Implementation
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a) Shorten of the Geometric Compression Stroke by means of an asymmetrical crank drive
b) Adapting of the Volumetric Compression Ratio (VCR) c) Very high Boost Pressure and intensive Intercooling
New Solutions for Atkinson Cycle Implementation at Aspirated and Turbocharged Engines based on:
Aspirated Engines Turbocharged Engines
Increased VCR in 3V
Relative Piston Displacement – Crank Angle diagram
Volume – Crank Angle diagram
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Simulation Results for Aspirated Engines
log(Pressure) - Volume diagram IFCE – Crank Angle diagram
SV = Standard Variant (classical Cycle for Aspirated Engines, Seiliger Cycle) 1V = SV + 100°CA Delayed Intake Valve Closing 2V = 1V + 90% Increased Volumetric Compression Ratio (VCR) 3V = 2V + Modified Crank Drive Note: AFR is kept in all these variants identical!
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+15% for 3V
Simulation Results for Aspirated Engines
6%
The losses caused by the suction and partial expulsion of the fresh charge in 1V & 2V are in 3V eliminated. As result a 15% higher value of the Indicated Fuel Consumption Efficiency is achieved in 3V related to SV & 2V.
In 3V the entire gas mass sucked in remains in cylinder for combustion. Although the compression stroke is much shorter, the sucked mass in 3V is 6% greater than in 2V.
Fluid Mass - Volume diagram IFCE – Crank Angle diagram
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3V-TC / SV-TC IFCE +17% IMEP +38%
Simulation Results for Turbocharged Engines at Full Load
The full potential of the very high boost pressure (ca. 16 bar) turbocharging can be used without exceeding of the maximal pressure (ca. 210 bar) and temperature (ca. 2100 K) on the cycle.
The VCR is reduced to 5.0 and the VER is enhanced to 27.0. The limits for maximal pressure and temperature on the cycle are respected, but the AFR are different!
Pressure - Volume diagram IFCE – Crank Angle diagram
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3V-TC / SV-TC IFCE +17% IMEP +38%
Simulation Results for Turbocharged Engines at Full Load
The losses caused by the suction and partial expulsion of the fresh charge are in 3V-TC eliminated. The piston work for compression is minimized by fully using of the high level of boost pressure (16.70 bar).
The VCR is reduced to 5.0 and the VER is enhanced to 27.0. The limits for maximal pressure and temperature on the cycle are respected, but the AFR are different!
Temperature - Volume diagram IFCE – Crank Angle diagram
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3V-TC / SV-TC IFCE +17% IMEP +38%
Simulation Results for Turbocharged Engines at Full Load
The losses caused by the suction and partial expulsion of the fresh charge are in 3V-TC eliminated. The piston work for compression is minimized by fully using of the high level of boost pressure (16.70 bar).
The limits for maximal pressure and temperature on the cycle are respected, but the AFR are different. The retained fluid mass into cylinder after suction is 12% higher as in 2V-TC.
Fluid Mass - Volume diagram IFCE – Crank Angle diagram
12%
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Procedure:
To facilitate the comparison the Ideal V,p,T-Model is introduced and the following parameters are kept identical in both Atkinson and Seiliger cycles:
1. expansion ratio 2. specific heat (heat per fluid mass) 3. AFR (air-fuel-ratio) 4. isentropic exponent 5. maximal pressure and temperature on the cycle 6. charge temperature of the fresh air after compressor and cooler.
The Ideal V,p,T-Model was validated by means of AVL-BOOST Simulation Tool
Analysis of Atkinson Cycle Implementation for Very High Boost Pressure Turbocharging at
Full and Part Loads
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Comparison between Seiliger and Atkinson Cycle for these Engines at Full Load
Pressure - Volume (left) & Temperature - Volume Diagrams of V,p,T-Seiliger and -Atkinson Cycles with same limits for maximal pressure and temperature
VCR
VER
AFR
IMEP
pC
TC
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Conclusions:
As result the Thermal Conversion Efficiency ηt in the Atkinson cycle reaches more as 25% as in the Seiliger cycle.
At the same time the Indicated Mean Pressure (IMEP) exceeds in Atkinson cycle with more as 70% that of Seiliger cycle under fulfilling of the same mechanical and thermal limits on both cycles.
Questions: 1. How is that possible?
2. Validate BOOST the simulation results of V,p,T-Model for the Atkinson cycle?
VCR
VER
AFR
IMEP
pC
TC
Comparison between Seiliger and Atkinson Cycle for these Engines at Full Load
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How is that possible?
Because in both cycles the temperature at the end of the filling are kept identical, is in the Atkinson cycle the sucked fresh charge mass much bigger as in Seiliger cycle (see figure).
That explains the much bigger indicated mean pressure of Atkinson cycle.
In addition the piston work for gas exchange processes becomes strong positive, i.e. this piston work is for Atkinson cycle only supplied and not in part consumed like in the case of Seiliger cycle.
Fluid Mass - Volume diagram
Comparison between Seiliger and Atkinson Cycle for these Engines at Full Load
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BOOST-Validation of Ideal V,p,T-Model for Very High Boost Pressure Turbocharged Engines
VCR VER
AFR IMEP
Pressure - Volume (left) & Logarithmic Pressure - Volume Diagrams of Atkinson Cycle as V,p,T- and BOOST-Models with the same charge pressure & temperature, IMEP and maximal Temperature on the cycle.
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Mass - Volume (left) & Temperature - Volume Diagrams of Atkinson Cycle as V,p,T- and BOOST-Models with the same charge pressure & temperature, IMEP and maximal Temperature on the cycle.
BOOST-Validation of Ideal V,p,T-Model for Very High Boost Pressure Turbocharged Engines
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Atkinson Cycle Implementation for Very High Boost Pressure TC Engines at Part Loads
The asymmetrical crank drive has the disadvantage that at part loads - because of the very extensive expansion - the cycle stops being feasible, i.e. the pressure at the end of expansion becomes lower than the ambient pressure.
For this reason, the crank drive should also enable the variation of the VCR!
Relative Piston Displacement – Crank Angle diagram of an
Asymmetrical Crank Mechanism with Variable VCR
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Atkinson Cycle Implementation for Very High Boost Pressure TC Engines at Part Loads
Correlations between: •TCE, •IMEP, •Boost Pressure, •Pressure & •Temperature before Turbine & •Energy balance at Turbocharger
The arrows show the combination of these parameters in an EOP (10 bar boost pressure and AFR = 1) & for the 1. Crank Drive Position
Enough Energy for Turbocharging
Not sufficient Energy
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• The TCE of the Atkinson cycle implemented in supercharged engines with
asymmetrical crank drive is more than 25% better and the IMEP exceeds
that of the Seiliger cycle by more than 70%, while meeting the same
mechanical and thermal limits in both cycles.
•The implementation of the Atkinson cycle by means of the asymmetrical crank
drive has the disadvantage that at part loads - because of the very extensive
expansion - the cycle stops being feasible, i.e. the pressure at the end of
expansion becomes lower than the ambient pressure. For this reason, an
asymmetrical crank mechanism is required which also enables the variation of
the VCR.
•By using such a crank mechanism, it is possible to realize Atkinson cycles for
part loads even with stoichiometric AFR and without throttling.
CONCLUSION
Thank you for your attention!