b y T i m v a n W a g e n in gen

- Motivation
- Concepts
- Performance Analysis
- Conclusions
- Questions
2 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

N a t u r e small
Atalanta project
Technology
3 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS scale → large

Micro Air Vehicle
Flapping Wing Mechanism
- Designed by Casper Bolsman
- 0.6 gram
- Performance estimate:
- 0.5 W power output
- Needed power density of system: 125 W/kg
- 6 minutes of flight time with
5% efficiency
4 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

MAV in Action
5 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

Hydrogen Peroxide
- Master thesis of Arjan Meskers at the PME department, TU Delft
- Chemical energy: high energy density
- Monopropellant
- Clean products: oxygen and water vapor
- Example catalysts: -Manganese oxide
-Silver
-Platinum
6 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

Catalytic Reaction in Action
7 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

Thesis Assignment
Find an engine concept that:
- is suitable for the MAV
- 125 W/kg
- 5% efficiency
- uses hydrogen peroxide as fuel
8 MOTIVATIONS -
CONCEPTS
–
PERFORMANCE I / II / III
-
CONCLUSIONS

Possibilities
9
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

+
+
Turbine
3 different approaches
Piston Cylinder
+ +
+
10
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

+
+
Concept I: Tesla Turbine Engine
+ Easy implementation
+ Theory of Tesla Turbine predicts good efficiency at small scale
- Conversion from rotation to linear motion
11
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

+
+
Concept I: Tesla Turbine Engine
12
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

+
Concept II: Otto Engine
+ Proven concept on regular scale
- Projects in literature show bad performance because of fluid leakage problem
- Implementation difficult
13
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

Concept II: Otto engine
+
14
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

Concept III: Hot Air Engine
+
+
+ Easy implementation
+ Promising scaling aspects because heat transfer is more effective
- Poor performance on regular scale
15
MOTIVATIONS
CONCEPTS –
PERFORMANCE I / II / III
-
CONCLUSIONS

Concept III: Hot Air Engine
+
+
16
MOTIVATIONS
CONCEPTS -
PERFORMANCE I / II / III
-
CONCLUSIONS

Performance
- What influences the performance of these concepts?
- Concept I
- Concept II
- Concept III
- Are the concepts suited for the MAV?
-Power density
-Efficiency
17
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Concept I: Tesla Turbine Engine
18
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Concept I: Tesla Turbine Engine: model
Assumptions:
Laminar flow
No entrance effects
Incompressible fluid
19
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Power Efficiency
Pressure difference
Length of belts
(radius of discs)
Height of gap
(spacing between discs)
20
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Measurements with small scale Tesla turbines
Pressure difference:
~20 kPa
Measured Performance
45 mW
18% efficiency
Estimated power density:
2 W/kg
[2] V.G. Krishnan et al. A micro Tesla turbine for power generation from low pressure heads and evaporation driven flows. Transducers, 11:1851 – 1854, June 2011.
21
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Concept I, Tesla Turbine Engine: conclusions
- Power density is too low: pressure difference must be increased considerably
- Simple model + measurements show that TTE is not suitable for the current size MAV
22
MOTIVATIONS
-
CONCEPTS
PERFORMANCE I
/ II / III
-
CONCLUSIONS

Concept II: Otto Engine
23
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Concept II, Otto Engine: combining 3 models
Catalytic
Reaction
+
Exhaust
Flow
+
Heat
Loss
24
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Catalytic Reaction: model
Drop on a catalytic surface
Similar conditions as during experiments
Energy Balance:
25
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Catalytic Reaction: model
[1] A.J.H. Meskers. High energy density micro-actuation based on gas generation by means of catalyst of liquid chemical energy. Masters thesis, TU Delft, 2010.
26
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Catalytic Reaction: high fuel concentrations
27
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Exhaust Flow: model
Compressible flow through a round nozzle
Based on momentum equation
28
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Heat transfer
Heat is transferred via
-conduction
-convection
-radiation
29
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

+
Concept II, Otto Engine: combining models
+ =
- Dealing with model uncertainties:
30
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Otto Engine: observations
-Reaction times are fast enough
-Trade off for fuel used per cycle
-Condensation in cylinder
31
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Concept II, Otto Engine:
Results
- Model shows performance above the current requirements of the
MAV
(125 W/kg @ 5% efficiency)
32
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Concept II, Otto Engine: considerations
- Model neglects:
- fluid leakage through cylinder/piston gap
- fluid friction at exhaust
- fuel delivery system
- Condensation in cylinder problem needs to be addressed
33
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I /
II
/ III
-
CONCLUSIONS

Concept III: Hot Air Engine
34
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Concept III, Hot Air Engine: models
Catalytic
Reaction
Heat
Reservoirs
Heat
Loss
+ +
35
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Concept III, Hot Air Engine:
Catalytic Reaction
Constant temperature
Mass balance
36
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Schematic
Concept III, Hot Air Engine:
Heat Reservoirs
Under reversible conditions
Estimate for heat transfer rates
- Using definition
Fouriers law
-Optimistic and pessimistic value
37
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

+
Model Results
+ =
Resulting performance of model
38
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Considerations for
Small Scale Hot Air Engine
- Model neglects losses of
- fluid flow between piston cylinder gap
- heat leakage of Decomposition Unit to the working fluid
39
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Conclusions for
Small Scale Hot Air Engine
- Heat transfer is not yet fast enough on this scale, which results in low performance
- Concept III is not suited for the MAV
40
MOTIVATIONS
-
CONCEPTS
PERFORMANCE
I / II /
III -
CONCLUSIONS

Overall Conclusions
- Of the considered possibilities, the small scale Otto engine is the best option for the MAV:
Power density at 5% efficiency:
Concept 1: << 2 W/kg
Concept 2: 245 – 440 W/kg
Concept 3: 0.5 – 8 W/kg
41
MOTIVATIONS
-
CONCEPTS
-
PERFORMANCE I / II / III
CONCLUSIONS

Overall Conclusions
Actual implementation of concept II requires more detailed analysis:
- Solving the fluid leakage problem
- Fuel pump
-Exhaust port
-Condensation
42
MOTIVATIONS
-
CONCEPTS
-
PERFORMANCE I / II / III
CONCLUSIONS

43
MOTIVATIONS
-
CONCEPTS
-
PERFORMANCE I / II / III
-
CONCLUSIONS
- END

44 DETAILED SLIDES

Scaling?
Scaling factor
Length
Area
Volume
16 PERFORMANCE
Engine 1
S = 1
L = 10
A = 10
V = 10
Engine 2
S = 0.5
L = 5
A = 2.5
V = 1.25

Approach of others?
6 PREMILAIRY RESEARCH

7 PREMILAIRY REASEARCH
Possibilities

Pressure difference
Length of belts
(radius of disks)
Height of gap
(spacing between disks)
40 PERFORMANCE
Power Efficiency

Energy flow in concepts
Carnot cycle =
7 CONCEPTS

Carnot Cycle
8 PERFORMANCE zero power output!

9 PERFORMANCE
Curzon Ahlborn Cycle

10 PERFORMANCE
Curzon Ahlborn Cycle

ND Curzon Ahlborn Cycle
11 PERFORMANCE

Basic thermodynamic engine model
- Two constant temperature reservoirs:
- Energy flows modeled with
Fouriers law of heat conduction:
-Carnot cycle between the working fluid temperatures:
17 PERFORMANCE

ND Curzon Ahlborn Cycle
18 PERFORMANCE

19 PERFORMANCE
Scaling of performance

Intermediate Conclusions
Efficiency of engine is independent of scale, if the cycle time is adjusted correctly
- Optimal power output can be found by finding the optimal cycle time
- Assuming an optimal engine configuration:
20 PERFORMANCE

12 PERFORMANCE
Energy Balance Model

13 PERFORMANCE
Energy Balance Model

14 PERFORMANCE
Energy Balance Model

Scaling of optimal cycle time concept 3 pessi opti
13 PERFORMANCE

Heat transfer
- Heat is transferred via
-conduction
-convection
-radiation
- FEM model in COMSOL
16 DETAILS

Heat transfer: FEM model results
16 DETAILS

Heat transfer: facts for MAV engine
- Low Biot number situations: not much use for insulation.
- Difficult to maintain a temperature difference within the system
- Loss term scaling exponent = 1.5
16 DETAILS

Intermediate Conclusions
- The performance of depends on a potential and the utilization
- Utilization is independent of scale
- How does this apply to the concepts?
15 PERFORMANCE

Catalytic Reaction: fundamentals
- Decomposition rate proportional to the effective contact area between fuel and catalyst
- Large Damköhler number: rate temperature independent
- First order reaction:
16 DETAILS

Exhaust Flow: model
Flow through a nozzle
Based on momentum equation
Neglects friction
32 DETAILS

33 DETAILS
Exhaust Flow: characteristics

Model Results: scaling
Assuming unrestricted cycle time!
24 PERFORMANCE

What about scaling?
Catalytic Reaction: Fluid Flow:
Power: Power Density:
Power Density at reference scale (S=1):
Power Density when size is 10 times smaller (S=0.1):
41 PERFORMANCE