Gas Engine Technology BV
Gas Engine Technology
GET is a research and development company dedicated to designing and manufacturing gas engine
controls.
GET's main field of interest is to combine their
knowledge about engines and electronics in order to
design and manufacture new controls. These control
systems not only offer economic benefits to the user
but also contribute to the protection of the environment.
One of GET's successful products is their anti-knock
control. In this field, GET is European market leader.
Engine Knock
During a combustion cycle a spark-plug starts-up the
ignition, resulting in a propagating flame front. Within
a normal combustion cycle this flame front runs
through the cylinder with a normal propagation
speed, gradually burning almost all mixture available.
Because of the lower temperature at the walls, the
flame front is extinguished short before reaching the
cylinder wall. This phenomenon is called "flame
quenching". This causes a so called "quenching barrier" or "boundary layer". This boundary layer isolates
the piston, cylinder head and cylinder wall against
excessive heat pick up resulting in a high thermal
load. If the methane number of (natural)gas (similar
to the octane number of petrol) drops, pre-reactions
can start to occur in areas which are not yet reached
by the flame front. In case of engine knocking, these
pre-reactions result in an un-controlled mode of combustion of unburned mixture with extreme high flame
propagation velocity. The onset of very high conversion rate causes the excitation of the natural frequencies of the cylinder charge inside the cylinder.
The resulting "pressure waves" and the coupling of
flame propagation with these pressure waves subsequently squeeze the isolating boundary and expose
the vital engine components to a high combined
mechanical and thermal stress. This will destroy the
piston - see picture- and can subsequently destroy
other components such as the cylinder liner as well.
a) Piston damage due to knock.
b) Surface structure damaged due to high thermal
load
Knocking combustion can be caused by e.g. un-stable methane numbers of the gas, a higher intake-air
temperature or a changing air-fuel ratio.
Gas Engine Technology BV
Analog versus Digital filtering
Knocking combustion results in vibrations propagated within the engine structure. These vibrations can
be sensed by Piezo electric transducers also called
knock-sensors. The signals coming from these transducers contain both knock-relevant frequencies and
background-noise.
There can be multiple knock-relevant frequencies
due to the several natural frequencies1 of the cylinder
charge. Especially with pre-chamber engines it can
be hard to distinguish knock-frequencies from background-noise. The filtering capability of an analog
band pass filter is very limited and will not enable a
knock detection system to be sensitive to all relevant
knock frequencies in the first place. It will also mess
up knock frequencies and back ground noise frequencies.
The principal limitations of analog filtering techniques
do result in an unsafe engine operation with less
power and a lower efficiency.
For this very reason GET, opposite to their competitors, does not use analog-, but the much more sophisticated digital-techniques, using a DSP based knock
detection system with real time - cycle by cycle- FFT
spectral analysis.
By using such analysis techniques it is possible to
exactly determine the 'signal energy' of the knockrelevant frequencies. Even when these frequencies
are positioned in multiple frequency bands. Using
these techniques allows the engine to run very close
to the knock-limit; the engine will run with improved
power and fuel efficiency in a guaranteed safe mode.
1 Natural frequencies can be calculated using the Bessel function
GET anti-knock control
Previously anti-knock controls only functioned as a
safety device to avoid damage. But, during the last
decade these have evolved into closed loop control
systems enabling the engine to run with the best possible fuel economy under changing gas quality and
ambient air temperature conditions. If an engine is
running under these conditions, it's critical to detect
knocking the best way possible. The GET anti-knock
controls are designed around the best filtering - and
analyzing techniques available today.
The analog signal from the knock-sensor runs
through an anti-aliasing filter after which it is digitized.
This digitized signal is filtered and analyzed by a
Digital Signal Processor (DSP). The DSP uses a
spectral analysis technique called Fast Fourier
Transformations (FFT) in order to convert the signal
from the time domain to the frequency domain. After
the signal has been processed, the knock-relevant
frequencies are extracted with ultimate accuracy
after which they are compared against certain thresholds. After this analysis, the knock-control parameters, e.g. engine global timing, cylinder individual
timing, load reduction, diesel injection timing (dualfuel operation) are adjusted accordingly.
The GET anti-knock control analyses each individual
cycle of each individual cylinder. The cylinder individual ignition timing is being changed, before the following cycle.
In case the applied ignition system requires that ignition timing is being changed engine-globally, the ignition timing of all cylinders is being retarded according
to the knock-level in the 'worst-case' cylinder.
With use of the GET anti-knock control it's possible
to optimize the ignition timing of each individual
cylinder resulting in improved
power and a higher overall
efficiency.
Result of Fast Fourier Transformation
Gas Engine Technology BV
Misfire detection
By analyzing the signals coming from the knock-sensors, the GET knock-control unit can also detect misfire. Depending on e.g. the condition of ignition
system a spark not necessarily starts a normal combustion. If for whatever reason there is no combusti-
on, the GET anti-knock control detects that and
informs the engine management.
This feature is optionally available.
Dual-fuel engines
GET anti-knock controls are not only being used on
dedicated gas engines. They've also been installed
on dual-fuel engines in order to change e.g. the
substitution rate or the diesel injection timing when
knocking combustion is detected.
With the GET anti-knock control, the pay-back time
of a dual-fuel retrofit will be reduced since the substitution rate is continuously optimized under
changing gas conditions.
Advantages of GET anti-knock control
A solid base for engine protection,
Based upon the best filtering techniques available,
Increased thermo dynamic efficiency,
Reduced loss of KWh-output during drop of methane index of fuel,
Knock-detection from cylinder to cylinder and cycle to cycle,
After 1 knocking cycle of 1 individual cylinder, the cylinder individual timing of that specific cylinder is corrected before the next cycle (under the condition that the ignition system supports this functionality),
Interfaces to all common ignition systems available in the market place (e.g. 4-20mA, CAN, RS-485)
Misfire detection available within the same anti-knock control,
Based upon a expandable platform,
Proven technology, over 1800 units supplied to almost all major European gas engine manufacturers.
Integration of AKC in GET engine management
GET has a total gas-engine management available
including e.g. air-fuel ratio control and speed-control. Such an integration of functionality not only
results into a large cost reductions, it also helps with
the optimization of all control-loops. If knocking is
detected, mixture can also be made leaner in order
to stop the knocking. Such optimization steps are
more difficult if different systems from multiple
manufacturers are controlling the engine.
Please contact GET with all off your engine control
questions, we will be happy to assist!
References
GET has supplied over 1800 anti-knock controls to
OEM's like GE Jenbacher, Perkins, Deutz MWM,
MAN B&W, BVI, Caterpillar/MAK and Wärtsilä.
A detailed list containing all engine types is available
upon request.
Gas Engine Technology BV
GET `s wide experience with AKC application
The GET anti-knock controls are designed around
the best filtering - and analyzing techniques available
today. The design of the anti-knock control is based
upon more than 10 years of experience with AKC
application and calibration on more then 45 different
engine types with cylinder bores ranging from 120
GET proprietary vibration analysis software package
mm up to 440 mm. GET has developed a proprietary
vibration analysis software package by which engine
application of the GET AKC can be realized with a
minimum of test bench capacity and/or down time of
the engine.
Gas Engine Technology BV
Specifications
Please note that these are 'general specifications'. GET designs tailored-made knock-controls which suit
seamlessly within the rest of the gas-engine or dual-fuel management.
GET can adapt to your requirements.
Dimensions
130 mm x 300 mm x 240 mm
Box position
The knock-control box must be mounted off the engine
Weight
4.15 kg
Max allowable temperature during -40°C - 85°C
normal operation
Power supply
24VDC
Power supply range
18VDC - 32VDC
Connector
Cannon type connectors
Conforms to following directives
EN55014, EN55022, IEC60529-IP65
Knock sensor
Bosch sensor with Cannon connector
1 sensor per cylinder or 1 sensor per 2 cylinders (double sensed mode)
Wiring between knock-sensors and knock control must be
according to GET specifications.
Maximum quantity sensors
20
Communication
CAN, J1993 based protocol
RS232 / RS485
Data content
Through the communication link the system status of the
knock-control and all individual cylinder knock-levels are being
communicated.
Input
2-stroke engine 1 pick-up sensing tooth on flywheel
4-stroke engine 1 pick-up sensing tooth on flywheel
1 pick-up sensing camshaft speed
Analysis technique
DSP performing spectrum analysis of the knock-sensor signal
using Fast Fourier Transformations
Capability
Cylinder individual and cycle specific knock-detection and control
Speed
Various speeds are supported ranging from 500 - 1800 RPM
Ignition
Cooperates with all industrial ignition systems available in the
market
Additional functionality
Misfire detection optionally available
Knock history diary short term and long termDiagnosis diary
Gas Engine Technology BV
Economiestraat 39
NL-6433 KC Hoensbroek
Phone +31 (0)45 56 30 584
Fax
+31 (0)45 56 30 287
Internet http://www.get-bv.com
E-mail info@get-bv.com