
Sept.2011 Transactions
of
Nanjing University
of
Aeronautics
&.
Astronautics Vol.
28
No.
3
CAUSALITY DIAGRAM BASED SAFETY ANALYSIS
OF
MICRO
TURBOJET
ENGINE
Di
ng
Shuiting
,
Bao
Mengyao
(School of Jet Propulsion,
Be
ijing University
of
Aeronautics and Astronautics,
Be
ijing ,
100191
,
P.
R.
China)
Abstract: An improved safety analysis based
on
the causality diagram for the complex system of micro aero-en-
gines
is
presented. The study
is
examined
by
using the causality diagram
in
analytical failure cases due to rupture
or pentration
in
the receiver of micro turbojet engine casing , and the comparisons are also made with the results
from the traditional fault tree analysis. Experimental results show two main advantages:
(1)
Quantitative analy-
sis which
is
more reliable for the failure analysis
in
jet engines can
be
produced
by
the causality diagram analysis;
(2)
Graphical representation
of
causality diagram
is
easier to apply
in
real test cases and more effective for the
safety assessment.
Key
words: micro turbojet engines; safety analysis; causality diagram; fault tree analysis; failure
CLC number: V235. 1 Document code:A Article ID:1005-1120(201
1)
03-0262-07
INTRODUCTION
Recent
studies
of
micro
turbojet
engines
draw
increasing
interests
due
to
their
tiny
de-
signed
sizes
and
special
purposes.
However
,
the
study
in
this
field is
not
trivial
because
of
the
con-
sideration
in
the
design
step
of
extreme
high
ro-
tating
speed
and
small
body
size
requirements.
Furthermore
,
the
complex
working
environment
causes
quite
a
few
issues
,
such
as
shorter
life
cy-
cle
,
difficulty
in
maintenance
,
as
well
as
high
cost
for
the
damage.
Since
applications
for
the
micro
turbojet
engines
are
extended
,
the
difficulties
in
the
structural
design
,
the
failure
modes
and
the
connections
among
these
failure
modes
increase
a
lot
,
which
require
more
considerations
in
the
de-
sign
and
manufacture
process.
All
of
these
lead
to
a
more
detailed
study
requirement
of
safety
analy-
sis
of
aero
engines.
In
addition
,
there
is
no
study
approach
is
generated
for
the
use
in
micro
turbo-
jet
engines
while
most
of
the
current
methods
are
generated
for
the
usual
jet
engines.
For
the
rea-
sons
mentioned
above
,
the
lacking
in
complete
understanding
in
this
area
drives
more
attention
and
research
in
the
safety
analysis
of
micro
turbo-
jet
engines
口
-2J
The
safety
analyses
of
civil
aerospace
system
and
equipments
are
described
in
Ref.
[3J.
Based
on
this
reference
,
the
traditional
methods
such
as
FT
A ,
RBD
and
Markov
,
are
not
quite
excellent
fit
into
the
micro
turbojet
engines
and
the
main
disadvantages
are
reviewed
as
below.
Firstly
,
for
the
complex
analytical
cases
,
the
CPU
require-
ment
for
the
calculation
grows
high
and
relations
are
still
difficult
to
achieve.
Moreover
,
for
the
coupling
causes
of
the
safety
issues
,
the
results
might
not
be
reliable
enough.
In
addition
,
the
re-
lation
consideration
of
time
and
conditional
proba-
bilities
is
neglected
in
these
approaches.
The
causal
diagram
introduced
in
this
paper
is
a
loop
directed
graph
,
which
introduces
logic
gates
into
the
network
and
dynamic
characteristics
into
topology.
The
results
show
that
this
diagram
can
give
effective
corrections
for
the
disadvantages
mentioned
above.
This
paper presents
an
improved
safety
anal-
ysis
approach
based
on
the
causality
diagram
,
which
is
verified
by
test
case
,
such
as
rupture
or
pentration
of
receiver
of
micro
turbojet
engine
casing.
With
the
description
of
the
analytical
pro-
Received date: 2010-12-20; revision received date: 2011-04-12
E-mail: bomeya@163.com