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MEMS as Fuel Injectors Patrick Flaherty ME 2082 Why use MEMS as - - PowerPoint PPT Presentation
MEMS as Fuel Injectors Patrick Flaherty ME 2082 Why use MEMS as - - PowerPoint PPT Presentation
MEMS as Fuel Injectors Patrick Flaherty ME 2082 Why use MEMS as fuel injectors? Quicker response time than conventional solenoid system More accurate control of fuel, higher efficiency Easier to obtain cleaner emissions, comply
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Why use MEMS as fuel injectors?
- Quicker response time than
conventional solenoid system
- More accurate control of fuel,
higher efficiency
- Easier to obtain cleaner
emissions, comply with emissions legislation
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Emissions Control Legislation
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MEMS as Fuel Injectors
MEMS technology with potential as fuel injection systems:
- Thermal Actuation
- Electrostatic Actuation
- Piezoelectric Actuation
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Thermal Actuation
- Technique is very similar to that
utilized by thermal inkjet printer, well understood
- Uses thermal energy to form a
bubble inside a chamber, which acts as a pump to eject a droplet
- Nozzle area atomizes the jet of
liquid, increasing efficiency of combustion
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Thermal Actuation
Principles of operation: Driving Force Velocity:
s s t v
P t P P t P + − − =
5 .
) exp( ) ( ) ( τ
∫∫
= +
2 1
) ( 2 1 mV dAdt t P mV
v
∫
= dt t P d V
v d
) ( 4 3
2
ρ
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Thermal Actuation
Penetration distance in air: Temperature profile
- f diesel fuel:
Clausius-Clayperon Equation:
5 . 1 2
1 195 . d V v x
a a d
ρ ρ =
− − + =
∞
) ( ) exp( 1
2
ζ ζ ξ π ρ erfc c k t q T T
d p d
t x
d
α ζ 2 =
fg v sat sat
h R T T T ρ σ 2 + =
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Thermal Actuation – Diesel Activiation Curve
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Thermal Actuation - Application
- Low penetration distance in air has not yet
been improved. May be improved by airflow-assisted injection.
- Diesel flashpoint of 71°C may cause
combustion in actuator
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Electrostatic Actuation
- Uses double-acting diaphragm pump to
inject fuel into the combustion chamber
- Originally researched as a potential
injection system for PDE, which requires a high degree of atomization
- Requires less energy than thermal
actuation, and is less temperature sensitive than piezoelectric actuation
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Electrostatic Actuation
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Electrostatic Actuation – Principles
- f Operation
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Electrostatic Actuation – Principles
- f Operation
2
12 h Lv P µ = ∆
2
8
h
R Lv P µ = ∆
Driving Force:
(Hagen-Poiseuille)
Total Force on Diaphragm: Electrostatic Force: Spring Force:
k e
F F F + =
[ ]2
)) ( ( 2 2 _ _
_ _
) ( 2 1 ) (
dielectric fuel r fuel dielectric r
G t y G dielectric r fuel r
- e
t V t F
ε ε
ε ε ε
+ −
= ) ( ) ( t y k t F
s k
==
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Electrostatic Actuation - Application
- Analytical models have been qualified
using an inkjet type of test setup
- Prototypes have been built, but
experimental data has not yet been
- btained
- Fabrication may prove to be challenging
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Piezoelectric Actuation
- The only method that is currently being
used in production engines (Denso, Siemens)
- Simple, easily manufactured
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Piezoelectric Actuation – Principles
- f Operation
Piezoelectric material exhibits strain in the presence of an electric field:
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Piezoelectric Actuation
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Piezoelectric Actuation - Application
- Rapid switch action, friction-free
- More precise dosing than solenoid
system
- Improved atomization
- Emissions reduced up to 20 percent
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Summary
- MEMS techniques (such as thermal and
electrostatic actuation) continue to be researched as options for fuel injection
- Piezoelectric actuation has been adapted
successfully in diesel fuel injection systems
- MEMS fuel injection, specifically piezoelectric,