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GET is a research and development company dedi-

cated 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 environ-

ment.

One of GET's successful products is their anti-knock

control. In this field, GET is European market leader.

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Gas Engine Technology

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 bar-

rier" or "boundary layer". This boundary layer isolates

the piston, cylinder head and cylinder wall againstexcessive 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 com-

bustion of unburned mixture with extreme high flame

propagation velocity. The onset of very high conversi-

on rate causes the excitation of the natural frequen-

cies of the cylinder charge inside the cylinder.

The resulting "pressure waves" and the coupling of

flame propagation with these pressure waves subse-

quently 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-sta-

ble methane numbers of the gas, a higher intake-air

temperature or a changing air-fuel ratio.

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Analog versus Digital filtering

Knocking combustion results in vibrations propaga-

ted within the engine structure. These vibrations can

be sensed by Piezo electric transducers also called

knock-sensors. The signals coming from these trans-

ducers 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 back-

ground-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 fre-

quencies.

The principal limitations of analog filtering techniques

do result in an unsafe engine operation with lesspower and a lower efficiency.

For this very reason GET, opposite to their competi-

tors, does not use analog-, but the much more sophi-

sticated 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 knock-

relevant 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

The GET anti-knock control analyses each individual

cycle of each individual cylinder. The cylinder indivi-dual ignition timing is being changed, before the fol-

lowing cycle.

In case the applied ignition system requires that igni-

tion timing is being changed engine-globally, the igni-

tion 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.

Previously anti-knock controls only functioned as a

safety device to avoid damage. But, during the lastdecade these have evolved into closed loop control

systems enabling the engine to run with the best pos-

sible 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 accuracyafter which they are compared against certain thres-

holds. After this analysis, the knock-control parame-

ters, e.g. engine global timing, cylinder individual

timing, load reduction, diesel injection timing (dual-

fuel operation) are adjusted accordingly. Result of Fast Fourier Transformation

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By analyzing the signals coming from the knock-sen-

sors, the GET knock-control unit can also detect mis-

fire. Depending on e.g. the condition of ignition

system a spark not necessarily starts a normal com-

bustion. 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.

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Misfire detection

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 sub-

stitution 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 cor-

rected 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-con-

trol. 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 Wrtsil.

A detailed list containing all engine types is available

upon request.

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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

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.

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GET `s wide experience with AKC application

GET proprietary vibration analysis software package

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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 kgMax allowable temperature during

normal operation

-40C - 85C

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 sen-

sed 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 con-

trol

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