CRDi_Pressure_Analysis

1
<master thesis> DTM-S 2016 w 40
Background
• During Engine testing knowledge about each injection of a diesel
injection process is important.
• Rail pressure trace contains information about injected fuel mass but
it is corrupted by pressure fluctuations.
• Therefore a method is required to determine injected mass from
pressure signal.
Recommended Decision, Resp.
• Basic method has been developed but practical applications need to
be worked out and implemented.
Purpose of this Presentation:
• Presentation of the thesis work carried out.
Previous Decision Fora
Forum Date Decision
Combustion team
group meeting
FIE team
CAE team
Section Technical Meeting
Department Technical Meting
Approved
Approved
Approved
Approved
Approved
Approved
Next Steps Date
• Implementation of multiple injections 05w40
Date Created: 2016-10-05Issuer: Thiyam Dannish, DTHIYAM, 97622, Security Class: Proprietary
Key Issues/ Strategic considerations
• Determining the right method to analyse the pressure signal.
• Water hammer influence on consequent injections.
• Mass flow derivation from pressure trace analysis.

Analysis of pressure trace in C.R system
and relation with injected fuel mass
Thiyam Dannish
Examiner : Bengt Tullgren (VCC)
Ingrid Andersson (LiU)
Supervisor : Ayolt Helmantel (VCC)
Joakim Wren (LiU)
21/9/2016 THIYAM DANNISH, DTHIYAM, 97622, SECURITYCLASS:PROPRIETARY 2

 BACKGROUND
 UNDERTAKING OF THE PROJECT AND THESIS AGENDA
 THESIS APPROACHES
 FINDINGS AND FURTHER WORK RECOMMENDATIONS
agenda
21/9/2016 3THIYAM DANNISH, DTHIYAM, 97622, SECURITYCLASS:PROPRIETARY

• CRDi system injects fuel under high
pressure and has flexibility to
control precise fuel amounts. There
fore multiple injection technique
can be used with this technology.
• Reduces engine vibration, engine
noise, emission by-products, fuel
consumptions etc.
• Necessary to predict the exact
amount of fuel that is injected to
compare or match different
injection processes and study
influences of different parameters
for a certain injection strategy.
Background

• Develop an online implementable
algorithm to predict injected fuel mass in
each injection events from the pressure
trace of multiple injection processes.
• Explored and conclude with a viable line
of research to achieve the main goal of
the project.
• Two approaches were conducted:
Implementation of a direct filter,
Simulating the recorded pressure trace
by modelling a parametric injection rate
profile.
Project goal and Thesis agenda

• Water hammer phenomenon caused by abrupt
shutting of the needle.
• Influence of this phenomenon on injected mass
of consequent injections.
• Understanding and isolation of the pressure
wave induced fluctuation from the injected
mass induced dip in the pressure trace.
• Ultimately predicting the injected mass by
analyzing the pressure trace.
Water hammer phenomenon

rigs IN VOLVO FOR DATA AQUISITION

Information derived from injector analyzer pump rig. Goal is to achieve the rate profile of pressure trace of engine rig.
Ultimate Goal of the project

Phase–I : Signal Analysis And Filtering

• Transformed signal from
time domain to frequency
domain using Fast Fourier
Transform algorithm.
• Exposure of all frequency
components present in the
signal for frequency analysis.
• Understanding the source
and dependency of these
frequency components so as
to narrow down the
frequency band significant
during injection to design
the filter.
Discretization of the signal into sine components

• Frequency divided into four categories namely,
 Pressure dependent
 Engine speed dependent
 Injection dependent
 Independent (pulse freq., etc.)
• Injection dependent frequencies will vary with change in separation time and also number of injections.
• Wave phenomena such as standing waves and water hammer are instigated during injection.
21/9/2016 8
Dependencies
THIYAM DANNISH, DTHIYAM, 97622, SECURITYCLASS:PROPRIETARY

21/9/2016 9
Pressure dependent frequency band
• Frequency depend on speed of sound in the
medium given by the relation
vel. of sound = 𝑤𝑎𝑣𝑒𝑙𝑒𝑛𝑔𝑡ℎ ∗ 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
• DOE with sweep in Rail Pressure keeping all
other factors constant(RPM , Injection number
etc.).
• Theoretical calculation of Standing wave
frequency of Rail approx. 2100Hz (f = K.v/2L)
and Water hammer frequency approx. 1100Hz
(f = K.v/4L).
• Coefficient of reflection of this waves is lesser
than 1 (due to various losses like viscosity etc.)
and therefore experimental results will be
lesser.

• DOE with sweep in the RPM.
• Frequency due to engine speed is
given by the relation
Engine frequency = RPM / 2*60
21/9/2016 11
Engine Speed Dependent frequency band

• DOE with sweep in
separation timing.
• Water hammer vibration
instigated each time there
is an injection and
therefore timing between
injections and number of
injections are a factor.
• Uneven energy distribution
in the band caused by
influence of phase change
in water hammer initiation.
21/9/2016 10
Water hammer frequency band

• DOE with sweep in
injection number
keeping all conditions
constant.
• Depend on the speed of
the engine therefore
must be present in the
engine dependent
frequency band.
• Determine the small
band of frequency that is
most significant only
during an injection.
21/9/2016 12
Injection Dependent frequency band

• Investigation carried out to expose
any kind of independent
frequencies present in the signal.
• Independent frequencies include
frequencies that may arise from
electric pulse, valve closure,
geometry of the system etc.
• Validation of presence of these
frequencies done by analysis with
no injection.
• No interesting frequencies present.
Independent frequencies

• Pressure dependent
frequencies eliminated.
• Engine dependent frequency
band up to 550 Hz do not have
a considerable change in their
energy content during
different number of injections.
• Focus is given on the band
between 550 Hz and 750 Hz as
this band has significant
amount of energy alteration
caused by injection number.
Elimination of frequencies

• STFT algorithm is a modified version of the
FFT algorithm displaying information in a
spectrogram of time and frequency.
• How does STFT work ?
• Performed on each frequency between
550Hz and 750 Hz thereby projecting the
energy content of that frequency in time
domain.
• Each ’filtered’ signal created by this was to
be analyzed and validated with the known
injected mass to determine the single most
significant frequency that is affected the
most during an injection.
Filter design technique (STFT)

 As mentioned discretized signal into segments.
 A derivative of the FFT algorithm and therefore require long signal length to give acceptable
resolution of frequency.
 Long signal segment dilute time resolution.
 Therefore information retrieved does not meet accuracy level demanded by the research.
 Information of the frequency contents in the signal.
 Pinpoint towards a specific band of frequency.
 Time-Frequency technique can be used for this project.
Reason for Unsuitability and inference

Phase–iI : CRDi model in dymola

• Model of the CRDi in dymola to capture
the water hammer fluctuation with
acceptable accuracy level.
• No needle mechanism installed and
therefore need to define flow behavior.
• The injection rate profile is given as an
input and tuned it to try and replicate the
pressure trace from engine rig (Reverse
Engineering).
• The model include as much flexibility that
is present in a real system so that the
exact analysis done in pump rig can be
replicated specially different injector
models.
Concept of the Model

• The rate of injection shape that is
produced during an injection
(BOSCH method)
Volvo Injection rate profile Measurement

Profile comparison at different pressure
• Trapezoid Pulse as a base model.
• Use of Bezier curve to replicated to and from the
maximum amplitude of rise and fall in the profile.
• Parametric model where all control points is adjustable
using relations and ’tuning’.

• Opening/energizing time of the needle.
• Duration of the injection event depend
highly on the operating pressure.
• Amplitude, rise and fall also depend on
the operating condition.
Injection rate Profile dependency
Operational Pressure
Amplitude
T_rise_1 P1 T_rise_2 T_rise_3 T_fall_3 T_fall_2 P6 T_fall_1

• Model is an approximation of the real system and therefore certain adjustments needed to get it working.
• Calibration process to fix initial constants of the model i.e. the inner dimension of injector.
• Comparison of the simulation results with pressure trace and injection rate profile from the injection analyzer dataset.
Calibration of the crdi model

• Time shift in order of 0.1ms. Maximum
pressure overshoot of 15 bar.
• Steady pressure level is equal for
simulation and experimental.
• There is pressure dynamics involved in
the engine cylinder whereas the
pressure is more or less constant in
injector analyzer.
• Since resistance of air is lesser than
diesel fuel the rate will be higher as
compared to data from injector
analyzer.
Comparison with engine data

 Method produces accurate results (97% match) for the present state.
 A strong groundwork for further research and analysis since the results
are within the acceptable range for a project in its budding stage.
 Extracted information not only for injected mass but injection rate profile.
 An example use of the information: Help in the research regarding
dynamics of fuel mixing inside the CC.
Inference from the study

 Foremost detalize the model adding more physics in,
..ex: cylinder pressure dynamics, friction model in rail,
..etc.
 Development of better relations defining the timings
..for control points.
 Eliminate variable parameters to make it dependent
..only on pressure and energizing timing.
 Introduction of multiple injections and determining its
..limitation (analysis on separation time).
 Start work on algorithm for online implementation.
The road ahead

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