The effect of Exhaust Gas Recirculation (EGR) on the emission from a lean-burner gas engine

Projektrapport

March, 1998

Dansk Gasteknisk Center a/s • D r. Neergaards Vej SB • 2970 Hørsholm • Tlf. 2016 9600 • Fax 4516 1199 • www.dgc.dk • dgc@dgc.dk

The effect of Exhaust Gas Recirculation (EGR) on the emission from a lean-bum gas engine

Per Pedersen

Danish Gas Technology Centre a/s Hørsholm 1998

TiLle

Re port Category

Author

Date of issue

Copyright

FileNumber

Project Name

ISBN

The effect o f Exhaust Gas Recirculation (EGR) o n the emission from a lean-bum gas en gine

Project Report

Per Pedersen

March 1998

Danish Gas Technology Centre a/s

717.65; H:\ 717\65\rapport\EGR report.doc

Experimental methods for reduction of emission from gas engines

87-7795-130-1

For servicesofa ny kind rendered by Danis h Gas Techno/ogy Centre a/s (DGC) tlze foliowing conditions shall apply

• DGC sirall be liable in accordance with "Almindelige Bestemmelser for teknisk Rådgivning og bistand, ABR 89"

("General Conditions for Consulting Services (ABR 89)"), which are considered adoptedfor the assignmenJ.

• DG C's liability per error and negligence and damages s uffered by the client o r an y t hird party is limited to

100% ofthefee received by DGCfor the respective assignment. The clie111 shall indemnify and hold DGC

harmless against all losses, expenses and claims which may exceed the liability of DGC.

• DGC shal/ - withour /imitation • re-perform its own services in conneelion with errorsand negligences con­

tained in the material delivered to the client by DGC.

Tilis reporl is copyright, and mustnot be reproduced in whole or in part without the prior written consent of DGC.

This English translation is providedfor convenience only and in case of discrepancy the Danish wording shall be

applicable.

July 1997

DGC-report 1

Table of Contents Page

l Introduetion .... .............................. .............. ... ..... ... ........................ ......... ........................... ....... .... 2

2 Summary .. ... .... ... .... ..................... ..... .. ......................................... .......... ..................... ... .. ... .. ... ..... 3

3 En gine, generator and contro l unit ............................................... .... .. ........ ..... ............................. 5

3.1 Engine ...................................... ... ...... ....... .... ............................... ....... .. ............................. ..... 5

3.2 Generator ................................. ..... ... ...... .. ...... .......................... ... ............ ......... ...... ..... .... ... .... 6

3.3 Control unit .............................. ........................................................ .. ......... ... .. ........ ... ........... 6

3.4 Operation ......................................................... ............. ... ................ ..................... ... .............. 7

4 Meters, analysers and data acquisition .... ... .. ..... ........................................................................... 8

4.1 Uncertainty ....................................... ............................................................................ ......... 8

5 Planning the experiments . . .. .. . .. . .. .. .. .. .. . .. .. .. .. .. .. .. . .. .. .. . .. .. . .. .. .. .. .. . .. .. .. . .. . .. .. .. . .. .. .. . .. .. .. . . . . . . . .. .. .. . .. .. l O

5 .l Range o f parameters .. .. .. .. .. .. .. . .. .. .. .. . .. .. .. .. .. .. .. . .. .. .. . .. .. .. .. .. . . .. . .. .. .. . .. . . . .. .. . .. . . . . .. . .. . .. . .. .. .. .. . . .. . .. l O

5.2 Succession of measurements ....................................... ................................. .............. .. ....... lO

6 Measurements ........................................................ .. .... ...... ..... ... .... .. ...... ...... .............. ....... ....... .. 12

6.1 Ignition timing and air/fuel ratio without EGR .................................................................. . 12

6.2 Measurements with EGR ....... ... ....................................................................................... .... 15

7 Closing remarks ..... ..................................... .... .................. ... ...... .. ...... ........ ... ..... ............ .......... .. 18

Appendix ....... ... ........ ... .. ..... ............ .... .......... .. ............. ...... ........... ....... .......... .............................. .. 19

Analysers .... ................ .................. ... ..... .. .. ..... ... ... ......... ........... ......... ...... ....... ................... ............. 19

Oz ............ ............................ ...... .. ....... ........... .................................................................... ........ . 19

NOx········· ·························· ············ ················· ····· ······ ············································ ············ ···· ····· 19 co ........ .................................. .. ..... .............................................. .. ........ ..................................... I9

THC .... ....... ........... ... .... .......... .. ............................................................................. ............. ........ 20

COz .... .......... ... ......... ..... ..... .. .... .. .. ..................... .............. .. ........ ... ...... .... .... ...... ... ... .............. ..... . 20

Literature .......... .. ....... ...... ............. .............. .......................................................... ..... .......... .... ...... 21

DGC-report 2

1 Introduetion

In recent years, attention has been focused on the emission of unbumed hy­

drocarbons in the exhaust gases from natura} gas engines. The stationary gas

engines instaHed in Denmarkare almost exclusively operatedasparts of co­

generation plants. The composition of unburned hydrocarbons is dominated

by methane, which is a greenhouse gas.

Emission of total unbumed hydrocarbons (THC) can be caused by many

factors, such as crevice volumes in the combustion chamber and overlapping

valves. Another factor is the mixture completeness. Running an engine on a

Iean mixture is an effective way of reducing nitric oxides in the exhaust

gases. The combustion temperature becomes lower leading to lower forma­

tion of nitric oxides (Zeldovich). Unfortunately, running anengine on a Iean

mixture has often an adverse effect on the emission of unburned hydrocar­

bons.

Several solutions such as catalysts and improved combustion are presently

being investigated. This project investigates the effect of using exhaust gas

recirculated to the air intake as replacement for air excess.

The work has been sponsored by the Danish gas companies and carried out

at the labaratory at Danish Gas Technology Centre a/s (DGC). Q/A on this

report was done by Brian Schmidt, DGC.

Hørsholm, March 1998

h J~' f Per Pedersen

Project Manager

Dept. of Gas Utilization

Bjarne Spiegelhauer

Viee-President

Dept. of Gas Utilization

DGC-report 3

Purpose

Results

2 Summary

Exhaust gas recirculation (EGR) is a well known method of centrolling

emission of nitric oxides from engines. It w as used on petrol engines befare

introduetion of the three-way catalyst. Recently, it has been re-introduced in

cernbination with the three way catalysts.

On automotive petrol engines smaller rates of EGR are utilised.

When larger rates of EGR are applied, it is known from various sources in

the literature - e.g. /2/ and /3/- that the THC content in exhaust gases in­

creases, and, eventually, severe misfires occur at about 30% EGR. In this

project, only smaller EGR-rates were investigated.

The project should demoostrate an indirect effect of EGR on the conten t of

total unburned hydrocarbons (THC) in the exhaust gases from a lean-bum

natura! gas engine.

When running a specific engine on lower air excess (without EGR), it is

known that the THC content in the exhaust gases is aften lower compared to

the THC content when running the engine on higher air excess. On the other

hand, nitric oxides will increase rapidly at decreased air excess. The forma­

tion of nitric oxides can be suppressed by the use of EG R.

A small rate of EGR has littie effect on the emission of THC according to

the literature. The indirect effect of replacing air excess with EGR should

thus be a reduction of the emission of THC.

The tests showed that a small amount of about l% (EGR) reduces the nitric

oxides signifieand y, with n o detectable undesired effect on fuel consump­

ti an or THC emission. This is the case for gas engines running moderately

lean (max. 50% air excess), and EGR can thus be recommended for these

engines. It lowers the conten t of nitric oxides, or the engine can be operated

on a richer mixture leading to reduced THC emission.

On engines running on ultra lean mixtures, EGR has littie effect, mostly

disadvantages.

The experiments reported here were carried out on a supercharged natura!

gas lean-bum engine instaBed in the labaratory at DGC. The engine has

been built into a mini co-generation unit comprising control unit, asynchro­

nous generator and heat exchanger. Emission characteristics have been re­

ported in an earlier project repart Il/.

DGC-report

Results without

EGR

Results with

EGR

4

The engine has since then been modified. Forthis reason, the emission char­

acteristics were re-investigated prior to the EGR experiments.

The emission of both NOx and unburned hydrocarbons is much lower com­

pared to the earlier engine layout. On the other hand, the emission of carbon

monoxide has increased and an oxidation catalyst is required in order to

fulfil the Danish legislation for CO 15/.

From samples of exhaust gases taken just after the exhaust manifold and

samples taken after the turbocharger, it was noted, that unburned bydroear­

bons were oxidised in the exhaust system. The effect is pronounced at low

air excess (A~ 1.5) and retarded ignition timing. With increased air excess,

the effect becomes negligible.

Hydrocarbonsis decomposed into carbon monoxide which oxidises further

to C02, but the last step takes place at a slower rate. Thus more CO is ob­

served in the exhaust gases after passage of the hottest part of the exhaust

system.

A small amount of cooled and dried exhaust gasses was feed back to the

induction system, after the carburettor at the suction side of the turbo­

charger. The amount was measured to be in the range of l% of the volume

of air consumed. This yielded almost 20% reduction in nitric oxides.

The results are similar to other EGR experiments on lean-bum engines re­

ported in the literature, but here the results are based on larger EGR rates.

See e.g. 121 and /3/.

DGC-report 5

3 Engine, generator and control unit

The complete unit comprising engine, generator and control unit has been

designed as part of a masters thesis by two students at the Copenhagen

Technical College. The work was done in co-operation with a company

manufacturing small co-generation units. The work was sponsored by the

Danish gas companies, and DGC carried out measurements of emission and

efficiency.

After the masters thesis, the unit was moved to DGC and installed.

3.1 Engine

The engine is a former Ford diesel engine converted by Power Torque for

natural gas operation under the designation SI4. It is a four-cylinder, four­

litre dispiacement engine.

The engine was not built for lean-bum operation, therefore some modifica­

tion has been made. In order to secure ignition and to maintain high power

output at a lean mixture, the ignition system has been changed and a turbo­

charger has been added.

The gas is mixed with air in an Impco gas carburettor. Mixture adjustment

c an be carried out manually, w hil e the engine is running. The throttle is op­

erated by a servo motor and a position sensor for remote control. After the

carburettor, the mixture is compressedin the turbocharger. After compres­

sion the mixture is cool ed in an intercooler (Mermaid type 4) to about 30-

400C.

The turbocharger is a Garret type T2 with waste-gate. The waste-gate allows

for manual adjustments of charge pressure, which makes it possible to

maintain the same power output at higher air excess.

Between the exhaust manifold and the turbocharger a reactor has been

added. It consists o f a l o o conical expansion from the manifolds, Ø 50 inter­

nal diameter on the flange up to 0129. Tubes of this diameter extends for

c a. l, 17 m through two rounded bendings, directing i t to the turbocharger.

Anether l o o con e contracts the diameter to match the turbochargers turbine

inlets. All pipes, cones and flanges are made of stainless steel.

DGC-report 6

The reactor was added as part of another project investigating the effect of

adding a strong oxidising agent to the exhaust gases. Both the manifold and

the reactor are insulated in order topreserve a high temperature in the ex­

haust gases and to avoid radiant heat. It soon turned out, that the reactor was

active by itself, oxidising more or less unburned hydrocarbon.

The original ignition system has been replaced by a Motortech IQ250 ca­

pacitive discharge ignition system. The ignition timing varies with engine

RPM after a linear relation. The setting can be manually adjusted or re­

motely controlled (not used). The selected spark plugs were Champion R.L.

85.G recommended by Power Torque.

The progress of combustion was briefly monitored by means of a Kistier

spark plug with pressure transducer. No signs of knock were ever detected,

regardless of operating conditions.

3.2 Generator

The engine is coupled to an asynchronous generator with a nominalload of

37 kW. The electricity generatedis disposed off by feeding it into the main

electricity supply.

3.3 Control unit

The engine and the generator is controlled by a PLC which takes care of

important operation and monitering tasks, such as starting the engine (using

the original starter motor), running the engine at idle for a few minutes be­

fore increasing the speed slowly to slightly above 1500 RPM. When the en­

gine has reached this speed, the generator is coupled online. Then the power

is increased slowly until output power reaches 37 kW. The PLC program

then maintains this load, while monitering coolant temperature and lubrica­

tion oil pressure during operation. If certain limits are reached, shut-down is

automatically initiated. At normal shut-down procedure, the load is slowly

reduced to O kW, then the generator is de-coupled and the enginespeed is

slowly reduced to idle speed, at which the engine is kept running for five

minutes in order to cool the turbocharger before stopping. Other conditions

will cause emergency shut-down.

DGC-report 7

The engine and the generator are encJosed in a noise-insulation housing. A

door at one end o f tbe hou ing provides access to the en gine. At the opposite

side of the housing, the control unit is placed. The conu·oJ unit has two

witches, a knob and an emergency stop button. A small display indicates

the engineload at normaJ operation. At error conditions, the display indi­

eates the error, e.g. missing oiJ pressure.

3.4 Operation

When normal engine load has been reached, the operator can manually over­

ride the part of the PLC-program centrolling the engine load, by turning a

switch into the MANUAL position and then, by turning a knob, either de­

crease or increase load until full throttle. Befare shutting down the engine,

the switch must be turned back into the AUTO position. Then the first

switch can be turned into the STOP position, and the shut-down procedure

starts. An emergency stop button is placed in the centre of the front panel.

All experiments were carried out in the MANUAL position, and the power

output was adjusted to 35 kW in every measurement.

DGC-report 8

4 Meters, analysers and data acquisition

During installation in the labaratory at DGC, the engine has been equipped

with a number of sensors and meters connected to a data acquisition system.

The sensors and meters are shown in Pigure l.

A number of measured values are instantly processed and shown on the dis­

play. This is the case for actual 0 2 and C02 in the exhaust gases and emis­

sion of NOx (NO and N02), CO and THC. Purther values shown are fuel

consumption, power and heat produetion and the efficiency of electricity

production. The acquisition system scans all chanoels at an interval of two

seconds. Measured and calculated values are stored in files.

Values of ignition timing must be read using a stroboscope and noted manu­

ally.

Intet manifold- pressure and temperature

Spark plug No l replaced by a Kistier spark plu whh pressure transducer

lntercooler

Temperature ol lubrtcation oll

Fuel - pressure and temperature Volume flow olluel

Temperature ol exhaust gases belore and alter turbocharger

Generator

F i g ure l: Location of the various meters and sensors

4.1 Uncertainty

The various meters and analysers contribute to the overall uncertainty on the

resulting values o f emission and efficiency. The foliowing tab le lists the

tolerance of the meters.

DGC-report 9

Min. Max. Values during Tolerance

experiments

Gas meter 1 m"/h 16 m~/h 10 m"/h ±1%.

Flow meter 0,05 m"/h 2,5 m"/h O, 1 m"/h ±3%. coolant flow

Electricity O kW 50 kW 35 kW ±0,5%

Pressure O bar 1 bar 0,3 bar ±0,6 hPa

manifold and gas

Barometer O bar 2 bar 1013 hPa ±0,5 hPa at 1 bar

Temperature 100°C 1100°C 680°C (exhaust) ±3,?DC at soooc NiCr/Ni Al

Temperature ooc 400°C 20°C (gas) ±0,3°C Pt 100 35°C (intake

manifold)

The gas analysers (Appendix l) were calibrated each day using test gases of

±2% relative uncertainty on the concentration. Prior to each measurement,

the analysers' ranges were c hanged if necessary, and se al e factors in the data

acquisition program were c hanged accordingly.

Analyser Measure d Relative uncertainty [%]

02 5,5 vol% ±4,7

co2 8vol% ±2,7

CO 1000 ppm ±3,5

NO x 700 ppm ±4,0

THC 150 ppm ±2,7

DGC-report 1 O

5 Planning the experiments

Previously, many measurements on stationary engineshave been carried out

maintaining certain conditions and then varied e.g. load, air excess, speed or

EG R.

In the literature these conditions are abbreviated as e.g.

WOT Wide Open Throttle

BPSA Best Performance Spark Advance

MBT Minimum advance for Best Torque

W e decided to carry out the measurements at a fixed load of 35 kW at vari­

ous values of ignition timing and air excess. First, we measured without

EGR in a wide range of air excess and a more confined range of ignition

timing. The EGR w as applied and som e measurements (at lo w air excess)

were repeated.

5.1 Range of parameters

According to the manual, the SI4 engine should be running at an ignition

timing at of 17° BTDC, when running on rich mixture. A lean mixture bums

at a slower rate, so higher ignition timings were considered to be of interest.

The various experimental set points were selected as 18, 20, 22 and some at

24°BTDC.

From earlier measurements it was found that a compromise between NOx

and CO was found at 50% air excess, A= 1,5. A range of A from 1,3 to 1,8

was selected.

Measurements with EGR were only carried out at the lowest air excess ra­

tios.

5.2 Succession of measurements

Ideally, the measurements should be situated equidistantly within a matrix.

For elimination of systematic errors, the succession should be in random

order.

DGC-report

In practice, it is rather time consuming to ad just air/fueJ ratio and subse­

quently engine power. Therefore, some rneasurements were carried out in

systematic succession. At fixed air/fuel ratio, the ignition timing, wbich is

much easier to handle, and subsequently engine power, were adjusted.

11

DGC-report 12

6 Measurements

Bach measurement takes approx. an hour. First, the engine is adjusted. Then

after a while, the engine has settled and the analysers read out more or Jess

constant values. Final adjustments of power output and air/fuel ratio must

then be carried out. After a while, the engine has settled again. Then the

actual measurements can take place. This willlast about 10 minutes. The

acquisition system scans all channels at a two-second interval, until 500

rows of data have been collected, then the program stops.

At constant load, a large amount of measurements w as carried out within in

a matrix of air/fuel ratio and ignition timing as deseribed in section 5.1.

Measurements were carried out at both the manifold and in the stack.

6.1 lgnition timing and air/fuel ratio without EGR

The ignition timing compensates for the burning velocity: if the engine runs

slowly, the charge maybeable to bum completely at a given ignition setting.

When the enginespeed is increased, the ignition must be advanced in arder

to allow the charge to be burned befare the exhaust stroke starts. Further­

more, the burning velacity is dependant on the air/fuel ratio. Atleaner mix­

tures, the charge bums at a slower rate. Finally, the flame paths and com­

bustion rates vary with the combustion chamber design and dimensions.

lgnition timing (the time when the spark is fired) is defined as degrees of

crank angle befare top dead centre (0 BTDC).

DG C-repart

ppm

21

lgnition timing [0 BTDC]

18 5

ppm

02 [vol %]

Pigure 2: CO measuredin samples taken in the exhaust manifold

ppm

lgnition timing [ 0 BTDC] 02 [vol %]

18 5

ppm

Pigure 3: NOx measuredin samples taken in the exhaust manifold

13

DGC-report

THC [ppm]

. . ~. . . . - ~

• • - l . . ·,

lgnition ["BTDC]

THC [ppm]

Oxygen [val%]

18 5

Pigure 4: THC measured in samples taken in both the exhaust manifold and in the stack

14

By looking at Figure 3 and Figure 4 it can be seen that when running at low

air excess, the engine produces unacceptable high levels of nitric oxides,

while the level of unburned is very low, especially in the stack. If nitric ex­

ides could be reduced without affecting the level of THC, the engine could

be run at lower air excess. This would yield an indirect effect of reducing

THC.

The particular engine used for the experiments hereis scrnewhat special, as

it has a large highly insulated volume just after the exhaust manifold - the

"reactor". The volume is about four times the swept v o l urne of the engine. It

is known from literature /4/, that hydrocarbon can be burned in the exhaust

at temperatures above 650°C and at relatively long residence time. As the

exhaust temperature from the engine used for this project reaches 680°C,

when the reactor is effective, some of the hydrocarbon will be oxidised,

which appears from the measurements shown in Figure 4. There may be

more complex reactions and this is being studied in anether project at DGC.

For commercial engines, a level of THC corresponding to the level marked

"Manifold" in Figure 4, or slightly lower, can be expected.

DGC-report 15

The level of carbon monoxides (see Pigure 2) is high, and as mentianed ear­

lier, there iseven more when measuredin the stack, due to the reactor. This

is no problem, as oxidation catalysts are effective in removing carbon mon­

oxide.

6.2 Measurements with EGR

If Pigure 4 is viewed from the right side, it willlook as follows:

10000

1000 e c.

.E!; 100 o :t:

• ; .. ~ ~ 1-

10 • 5 6

... .. ~ ... ~

....

7 8

0 2 [vol%]

, •

9 10 11

• THC without EGA

Figure 5: THC versus 0 2 in exhaust gases. As many different ignition timings are represented, the data is sarnewhat scattered.

It is seen that a significant increase in THC eecurs at increased air excess.

It was decided to apply EGR at air excess corresponding to 5.5% 0 2.

Exhaust gas was lead though a coil providing cooling to at bottle calleeting

condensed water. The dry gas was measuredin a flowmeter with a full scale

of 65 litre/minute.

Measurements were then carried out at several ignition timings, and the rate

of recirculated gas w as kept constant at l% based on valurnes at normal

condition.

DGC-report

1000

900

e Q. 800 B d 700 z

600

500

>.

5.50 5.52 5.54 5.56 5.58 5.60

Figure 6: 18° BTDC

1000

900

'[ 800 ~ d 700 z

600

500

• o

0 2 [vol%]

• .....

+ NOx w ithout EGA

o NOx w ith EGA

• NOx w ithout EGA.

o NOx with EGA

5.40 5.45 5.50 5.55 5.60 5.65 5.70

0 2 [volo/o]

Pigure 7: 20° BTDC

16

DGC-report

1300 1250 • 1200

E 1150

c. 1100 ~ 1050 & 1000 z 950

900 850 800

5.45

Figure 8: 22° BTDC

1400

1300

E c. S: 1200 )(

o z 1100

1000 5.45

Figure 9: 24° BTDC

6 ...,

5.50

0 2 [vol%]

~ •

o

5.50

0 2 [vel%]

5.55 5.60

5.55 5.60

• NOx w ~hout EGA

<> NOx w ~h EGA

+ NOx without EGA

<> NOx wilh EGA

The figures show reductions in the range of 15 to 20% of nitric oxides.

17

No direct effect of EGR on THC was seen. No detectable difference in fuel

consumption or electrical efficiency between load with or without EGR w as

observed. It is assumed, however, that the electrical efficiency will decrease

at increased EGR and maintained 0 2 content in the exhaust gas.

DGC-report 18

7 Closing remarks

During the experiments, it became clear that the rate of EGR should be de­

termined by other means than a flowmeter. When using flowmeters, the ex­

haust gases should by dried. Otherwise, the flowmeter becomes fouled by

condensate. A better way is to measure C02 both in exhaust gases and in

combustion air after mixing.

W e did not achieve levels of nitric oxides fulfilling the Danish legisla-

tion /5/. To do so requires higher rates of EGR and slightly higher air excess.

Our best guess is to run the particular engine at 6% 02 and to increase the

EGR rate to 5-7%. Unfortunately, there was no time to verify this.

More literature on EGR has been published since this project was initiated.

It is well documented in the literature, that a reduction of nitric oxides of

50% can be achieved by using EGR rate of about 7%. There is reported no

significant increase in THC emission at this level /2/. EGR has littie effect

on engines running on very lean mixtures, due to smaller contents of water

vapour and C02•

Finally, attention should be paid to cerrosion and wear problems w hen es­

tablishing EGR on commercial natural gas engines. Water vapours condense

in the pipe leading exhaust gases to the inlet. Droplets could damage the

turbo charger and if materiais such as copper are used for EGR pipes, corro­

sion could present a problem to the engine.

DGC-report 19

Appendix

Analysers

The sample of flue gas was cooled, filtered and dried in an air conditioner

before being fed into the analysers.

The instruments arelabelled (DGC No.) and a log is kept for each instru­

ment.

The analysers w e re calibrated every da y using test gases o f ±2 o/o relative

uncertainty. The test gases used were the following. The bottles oftest gases

are replaced minimum each year.

Manufacture

Type

Range

Accuracy

DGC-no.

Manufacture

Type

Range

Reproducibility

Lineari ty

DGC-no.

CO

Manufacture

Type

Range

Reproducibility

Servemax

572 - paramagnetic

O- 25 vol. o/o

± 0.1 vol. o/o

201

Thermo Environmental Instruments Ine.

lOA/R

from O- 2.5 to to O- 10.000 ppm

l o/o of full scale

±l%

302

Hartmann & Braun AG

Uras 3 G

from O- 200 to O- 2.000 ppm

~ 0.5% of full scale

DGC-report

l Linearily

DGC-no.

THC

Man u faeture

Type

Range

Accuracy

DGC-no.

Man uf aeture

Type

Range

Reproducibility

Lineari ty

DGC-no.

20

±l %1 402

Analysis Automation Ltd.

523

from O- 2.5 ppm to O- 10.000 ppm

± l vol. % o f range

601

Hartmann & Braun AG

Uras 3K

O - l O and O - 20 vol. %

::::; 0.5% of full scale

::::;±1%

501

DGC-report

Uterature

Pedersen P.: Measurements of emission from a lean-burn gas engine. Hørsholm: Danisb Gastechnology Centre, 1997.

2 Raine, R.,R.; Zhang, G.; Pflug A.: Comparison of Emissions from Natural Gas and Gasoline Fuelled Engines. SAE paper 970743, 1997.

21

3 Johansen, Bengt; Docekal, Daniel: Effekt av A., EGR ocb tandvinkel på emissioner och virkningsgrad i en konverterad naturgasmotor. Lund: Lunds Tekniske Højskole, 1995.

4 J., B., Heywood: lnternal Combustion Engine Fundamentals. McGraw­Hill International, 1988.

5 Miljøstyrelsen: "Bekendtgørelse om kvælstofilteforurening mv. fra gasmotorer og -turbiner", bekendtgørelse nr. 688 af 15/10-1990