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SAE TECHNICALPAPER SERIES 1999-01-0568

Water Injection Effects In ASingle-Cylinder CFR Engine

R. LanzafameUniversity of Catania - Engineering Faculty - Machinery Institute

Reprinted From: Combustion in SI Engines(SP-1436)

International Congress and ExpositionDetroit, Michigan

March 1-4, 1999

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ISSN 0148-7191Copyright 1999 Society of Automotive Engineers, Inc.

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1

1999-01-0568

Water Injection Effects In A Single-Cylinder CFR Engine

R. LanzafameUniversity of Catania - Engineering Faculty - Machinery Institute

Copyright © 1999 Society of Automotive Engineers, Inc.

ABSTRACT

Though analysed by a few researches, the practice ofwater injection in Spark Ignition Engines (SI-ICE) doesnot yield homogeneous results, owing to various typolo-gies of engines used for experiments.

In this paper the effects of water injection in the intakepipe are investigated from both a theoretical and experi-mental viewpoint. Pressure vs. time diagrams wererecorded on a single-cylinder CFR engine at AGIPPETROLI, Priolo (CT).

Tests were performed according to Research and MotorMethod (ASTM). Water was supplied by a continuousinjection system inclusive of comparatively high pressurepump. The engine was fed with low O.N. base gasoline(cheap products, intermediate of refinery processes).The water to fuel mass flow rate ratio was varied in therange 0 to 1.5.

The NOx emissions measurements confirm the tremen-dous effectiveness of water injection in reducing theengine environmental impact.

Test data have been used to implement a detonationmodel that allows to predict water injection effects.

Results have shown that water injection really representsa new way to avoid detonation, to reduce compressionwork and to control NOx formation in SI engines.

INTRODUCTION

The use of water as supplement to fuel-air mixture hasbeen considered repeatedly since the early developmentof internal combustion engines (ICEs). Water has beenadded as an internal coolant, as a knock suppressantand a means to control emissions. Observations gener-ally regard water effects on engine performance, knockand emissions.

Clearly the practise of water injection in ICES is not new[1], but nowadays it is considered carefully for the bene-fits it allows. The most important are the current require-ment for raising the octane number (O.N.) of fuel (for thereplacement of the primary anti-knock additive in petro-leum refining technology), and the reduction of NOxemission in the exhaust gas.

Early designs of high compression ratio aircraft pistonengines employed a water vapour induction system toincrease the fuel anti-knock rating and engine output.With 10% injection of water1, during intake stroke fueloctane rating is boosted about 2 to 4 units with simulta-neous increases in the engine output of 30 - 50 % [2, 3].

The use of water-fuel emulsion for control NOx emissionwas described by Nicholls [4]. It was found that 10%water in gasoline caused 10-20% reductions in nitrogenoxides. Bignardi et al. [5], while proposing a kineticmodel, computed the composition, temperature, internalenergy and nitric oxides content of the exhaust gas,under influence of water added to fuel.

Russian researches, Satpov and Lusho [6], havereported the effects of water presence in fuel on SIengines. They indicated that the NOx content in exhaustgas dropped by 1.3 % for 1% addition of water to emulsi-fied fuel.

All observations are attributed to a cooling effect due tothe high latent heat of vaporisation of water and to awater induced slow-down of the combustion process.Direct test evidence on latent heat effects and on waterinduced changes in combustion rates does not yieldhomogeneous results, owing to various typologies of theengines used for experiments.

In this paper the effects of water injection in the intakepipe of a single cylinder CFR engine was investigated.Tests were performed at AGIP Petroli Fuels Control Labo-ratories, Priolo (CT), according to Research and MotorMethod (ASTM).

Water was supplied by a continuous injection systeminclusive of a comparatively high pressure pump. Thewater nozzle (De Lavan - 45° spray, 0.2 gal/h under thepressure of 1 MPa), was located in the intake manifolddownstream from carburettor, shortly before the inletvalve. Engine test data with base fuel and gasoline-watermixture were compared to identify the water injectioneffects.

Actually, the instability of the emulsified fuel2 was themain disadvantage encountered in the utilisation of

1. Water per unit fuel (volume)

2

water-fuel emulsions. Moreover it is necessary to createthe emulsion shortly before its introduction in the com-bustion chamber since no emulsion promoter wasemployed3.

EXPERIMENTAL APPARATUS

A standard engine4 arrangement and instrumentationwas utilised except for:

• a piezoelectric pressure transducer located in theknock plug hole;

• a positive displacement water pump;

• a piezoelectric pressure transducer mounted at theinner surface of the intake pipe;

• a charge amplifier;

• a digital data recorder system;

• a modified intake pipe provided with a special waternozzle.

Part of instrumentation set-up and some parts of themodified engine are shown in fig.1. Table 1 shows a list ofthe main technical properties of experimental devices.

Pressure data were recorded, as well as crank-angle by astorage oscilloscope data system. Motoring pressuretrace was also monitored immediately following the firedcycle by shorting instantaneously the primary circuit ofengine ignition. Fuel consumption was measured using a100 ml burettes and a digital electronic counter. Air flowinto the engine intake pipe was measured by a calibratedVenturi flow meter. The intake pipe was provided with aspecial water nozzle expressly built in order to allow con-trolling water injection rate.

Fuel was introduced at the carburettor “Venturi” (9/16”)via standard jet. Adjustment of fuel and water flow rates,to the engine, was obtained by varying water supply pres-sure (in the range of 0.5 to 2 MPa), fuel head, and bycontrolling water back-flow to the pump suction, bymeans of a fine needle valve.

A fitting was introduced amid the standard intake pipe sothat the water nozzle was properly located. Pipe wallswetting was minimised and interference was avoided with

gasoline spray. A scheme of the modified intake pipe withwater injector is shown in figure 2.

Exhaust emissions of CO and CO2 were monitored with anon-dispersive infrared analyser (NDIR), unburnedhydrocarbons by a flame ionisation detector (FID), andoxides of nitrogen were measured by chemilumines-cence method after dilution with zero air.

FUELS

Several blended gasolines produced at AGIP Petroli,coming from "CR30" plant, were tested at AGIP Experi-mental Fuel Control Station, both Research and Motormethods. However better results have been found outover a base product called “BL2 CR30”5 rated at 64O.N.M.M (68 O.N.R.M.).

Table 2 shows a list of some of the physical and chemicalproperties of this base gasoline.

It is well known that fuel octane quality limits performanceand efficiency on SI-ICE. Gains can be achieved by bothdesign provision and refinery processes.

The reduction of the amount of anti-knock additive sub-stances consequent the use of water injection as anti-knock system would have a remarkable implications fromat least two points of view:

• keeping the real cost of industrial product low;

• minimising the engine environmental impact.

These two concepts form together one of the aim of thispaper.

LABORATORY ENGINE TESTS

It is widely accepted that the audible knock in SI enginesis caused by pressure waves due to very fast heatrelease. Such fast combustion cannot occur from themechanisms that govern normal turbulent flame propa-gation but rather from chemical reactions proceeding inthe unburned gas ahead of the flame front which makethis end gas auto-ignite almost instantaneously.

At the end of the suction stroke, finely atomised, liquidwater gasoline and gas are compressed. The vaporisa-tion of the liquid will cool the gas and consequently lesswork will be required for the engine compression stroke.At the same time, the liquid whose vaporisation isdelayed until the piston is in the neighbourhood of TDC,requires a negligible compression work, while, later invapour phase, it is able to supply the piston with signifi-cant expansion work. Water, with its high latent heat, isparticularly suited for this purpose.

2. The practical implementation of this concept involves the solution of many technical prob-lems because the production of a high quality emulsion is required whilst the add-on kits used to retrofit the existing engines should result as compact, reliable, and cheap as pos-sible.

3. Several techniques are under investigations for emulsion product, based on mechanical (ranging from high pressure homogenization to cavitation and ultrasonic phenomena) or chemical concepts.

4. Waukesha Engine Division – Dresser Indus-tries , Wisconsin, USA.

5. This is a Virgin Naphtha coming directly from topping plant .To increase the original O.N. M.M. to 85, typical of commercial fuel, major total cost is about 45-50 $/ton.

3

Comparative tests show that a noticeable change in com-pression pressure does not occur until approximately 20deg BTDC as it is shown in pressure – crank angle dia-grams of figure 3.

The decrease in compression pressure corresponds toless than 20% vaporisation of the injected water. Toobtain this scope, the intake temperature was raised to6

416.2 K while the engine speed was kept 900 r/min. Withlower intake temperatures, vaporisation was negligiblesince no appreciable pressures reductions weredetected.

Experimental test data show that water injection into anunheated manifold, when the engine speeds is reason-ably high, will not give water a sufficient time to vaporiseduring the compression stroke. Of course, in normaloperation of a naturally aspirated engine the water doesnot vaporise until after combustion is well under way. Thiseffect well explains why injection of water into very highlycompressed or supercharged engines has been suc-cessful.

During combustion development the maximum peakpressure location, as it is shown in figures 3, 4 indicateshow well the engine can transform its gas pressure intooutput work due to the beneficial effects of the waterinjection. The results covered up to this point demon-strate the influence of water injection on the efficiency atconstant value of the compression ratio. The substantialadvantage obtained by water injection regards the regu-lar combustion development that should be impossible,otherwise. The comparison with detonation mode leadsto the consideration that the engine can operate at themaximum non knocking compression ratio, then its effi-ciency can be increased.

It is well evident that water injection slows the combustionprocess down in SI engine. Thus to maintain standardMBT spark setting the timing should be advanced duringtest, when using water injection gasoline combinations.Unfortunately such a procedure has not been performed,because the available test rig was not provided withdynamometer.

It is worth to know that keeping the spark advance con-stant while increasing the water rate leads to a loss ofpotential piston work gain.

In the following figs. 4,5 are shown p–V diagrams thatdemonstrate the influence of the water injection/fuelmass ratio “s” 7 , in the work cycle, at constant value ofthe volumetric compression ratio (r) and the maximumnon knocking r value, at constant “s” for a fixed fuel.

Based on this result the efficiency gain can be obtainedby taking advantage of the octane quality of water / gaso-line combinations only.

Several octane tests on different base gasoline accordingto R.M. were carried out and experimental results areshown in Table 3.

As mentioned in an earlier section, all experimental find-ings were normalised with respect to the data obtainedusing base gasoline at standard spark advance. Theinfluence of water injection was experimentally measuredand best results were carried out using base gasolinecalled “BL2 CR30”.

Effects of water injection over octane tests in accordancewith both Research and Motor methods, are shown for afixed fuel in fig. 7.

As it is shown in fig. 7, using base gasoline with waterinjection, the R.M. octane number rose from 70 ÷ 93, andM.M. octane number rose from 64 ÷ 90, while “s“ wasvaried in the range 0 ÷1.5.

The better beneficial effect of water injection appears inthe field of 1.25 “s” value.

The exhaust temperature did not significantly change forrich mixture conditions when water was injected in therange of 0.5 water injection rate. However for water injec-tion rate of 1 ÷ 1.50, exhaust gas temperaturesdecreased somewhat. Shown on the fig. 8 are theexhaust temperature changes which were measured dur-ing engine tests. Water injection increased the total massof charge in the cylinder since the air fuel flow rates wereheld constant for each test. Thus most of the observedtemperature drop can be accounted for by the increaseddilution of the charge.

Also NOx, HC, and CO/CO2 concentrations in theexhaust gas, were detected under standard knockingintensity with and without water injection.

NOx emissions were significantly reduced with waterinjection and this reduction was present in any case. TheNOx level was reduced more then 50 %, while water / fuelratio was about 1.50. The NOx levels for the fixed fuel,are plotted versus water to fuel mass ratio (0 ≤ ”s” ≤ 1.5)and diagram is shown in the fig. 9.

The effect of water injection caused a small drop in car-bon monoxide and hydrocarbons emission increased,probably due to change in quench layer thickness andgas temperatures. However this hydrocarbons increase isrelated to the fuel components and chemical participants.

DETONATION INDEX

It is well known that auto-ignition of perfectly homoge-neous mixture is controlled by factors such astemperature, density, turbulence and chemical composi-tion of fuel. Starting from the consideration that the pre-flame reactions of a real mixture in a real engine beginearly during the compression stroke and continue at an

6. In standard CFR engine the temperature con-trol set is provided in °F

7. In the following context it is meant by water injection rate, the ratio of water to fuel mass flow rate.

4

accelerating rate as the compression pressure and tem-perature increase, compression and combustion eventsare hereinafter considered.

Water injection into air-fuel mixture affects parameterssuch as instantaneous gas temperature and heat transferrate. Since these variables are extremely difficult to mea-sure experimentally, pressure data were processed.

An engine cycle study that models the compression andcombustion processes is implemented and proposed inthe following.

Thermodynamic effects of water injection spark ignitionengine are considered. To better demonstrate thesechanges in work cycles, pressure-volume (p-V) diagramsare considered in order to develop theoretical calcula-tions.

As far as a mixture of only gasoline and air is induced intocylinder, standard methods can be employed in order tocalculate the instantaneous gas temperature from cylin-der pressure data.

Suitable assumptions are usually introduced, about thefuel evaporation process, that are reasonably in accor-dance with experimental evidence (i.e. all fuel in vapourphase at intake valve closure).

Unfortunately no such assumption can be made forinjected water, whose lower vapour pressure and higherlatent heat cause vaporisation to be delayed well after thebeginning of the compression stroke.

In order to estimate the instantaneous gas temperaturevalue into combustion chamber a mathematical modelhas been developed starting from experimental data car-ried out in CFR engine tests.

A gas mixture composed of air, fuel, ad water have beenconsidered. This assumption of “pseudo-fluid”8 allows todetermine the correct value of the mixture constants Ruand Rb for unburned and burned gas, by comparinginstantaneous values of experimental gas pressure andmaximum value of gas temperature carried out duringmotored engine tests.

In order to develop a model that allows to define a deto-nation index to predict this phenomenon, a thermody-namics calculation for compression stroke andcombustion process is implemented.

The combustion chamber was divided into two regions:unburned and burnt. The charge was assumed to becomposed of ideal gases (frozen in the unburned gasregion and in chemical equilibrium in the burnt gasregion), and the first law of thermodynamic, equation ofstate, mass and volume conservation were applied to theburnt and unburned gases.

The pressure was assumed to be uniform throughout thecylinder and r first order ordinary differential equations

can be obtained for the pressure, mass, volume, compo-sition, and temperature of the burnt and unburnt gases.

In this model the two zones are separated by a sphericalsurface of discontinuity (the flame front). The model wasbased on the assumptions that the flame front was ani-mated by radial advancement and leakage flows intocrevices were neglected.

The equations governing the burnt and unburnt gaszones can be written as:

where the subscription u indicates the unburnt gases andthe subscription b indicates the burnt gases.

Note that:

where dmc/dθ is the combustion or mass burning rate.

In absence of leakage flows into crevices:

8. The remaining vaporization rate will be devel-oped during combustion process.

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During combustion phase the mass burnt fraction wasdefined as follows, according to Wiebe model.

This set of equations is not closed (i.e. there are moreunknowns than equations). Closure can be achieved byspecifying the mass burning rate dmc/dθ and the geome-try of the flame front.

Thanks to this water mass burning rate it is possible totake in account the “vaporization degree” of water duringcompression stroke. Calculated values of gas tempera-ture and pressure during compression stroke are shownin figs 10 and 11 for different water mass flow rate.

Details of this model are reported in [7].

Detonation phenomena depend on the story of pressureand temperature of the end gas in a variable time range.

Pre-reaction, during this time, within the unburned frac-tion may be completed with the consequence of auto-ignition presence into the gas fraction. The upper limitand lower limit of the reaction time are variable. In ICEsthe lower limit is identified with the time of the ignition(starting of the combustion t0). According to the theory ofLivengood and Wu [14], the portion of the pre-reactionthat occurs in the generic time t subsequent the startingtime t0, can be represented in the following form:

where τ is the instantaneous time delay, as a function ofpressure and temperature.

This equation allows to determine the time tdet. when thedetonation starts (if it is present), because the equationcan be written in the following form that describes thetrend of the pre-reaction in the all field of the time delay:

Using this equation, it is possible to predict the onset ofthe detonation, when the value of tdet. is fixed, assumingtdet. as the instant in which the maximum pressure incombustion chamber is achieved. Thus the followingidentity can be written as:

To evaluate a detonation index, it is necessary to specifythe expression of the time delay as function of pressure,temperature and mixture strength.

According to several authors [7, 13], this expression canbe written as:

where A, B, C are constants depending on the mixturefeatures. In this case the values of constants are:

where O.N. is the octane number of the fuel.

Then, not knocking conditions can be represented by :

where n is the engine speed and 0, p max are respec-tively the crank angle when the combustion begins, andthe crank angle at combustion peak pressure value onthe normal9 cycle.

Thus it is possible to define an index that allows to knowwhether the detonation occurs or not. The expression forthis index is:

For the not knocking condition it is found:

The term at the right hand of this equation can be inter-preted such as a “detonation index required” 10 from thefuel and the left hand such as a “detonation index avail-able” for the engine. The first index depends on fuelcharacteristics exclusively, while the second onedepends on the engine features only.

Detonation index required and available versus watermass flow rate are shown in figs 12 and 13. It is possibleto underline that detonation margin grows up when fuelO.N.M.M. runs from 65 to 90, according to diagrams

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9. Normal cycle is the cycle optimised for the maximum mean pressure.

10. Note the analogy with pumps.

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shown in figs 4, 5 and 6. The detonation index required(blue line in fig. 12) decreases while the water to fuelmass ratio grows up from 0 to 1.5 according to diagramsshown in figs 4, 5 and 6. The detonation index available(red line in fig. 12) increases while the water to fuel massratio grows up according to diagram shown in figure 7.

TABLES AND FIGURES

Table 1.

Description of Device ModelData Acquisition Board AX5412 High SpeedPiezoelectric Transducer located in the knock plug hole

Kistler 7063

Piezoelectric Transducer mounted in the inner sur-face of intake pipe

Kistler 601A

Charge Amplifier Kistler type 5007Position Transducer Elettroprogetti s.a.s.Thermocouple Type K (NiCr-NiAl)

[ 0°C ÷ 1260°C ]Water Nozzle Delavan 45° spray

0.2 gal / hPositive Displacement Water Pump

Bosch 9 / 100

Rated delivery pressureRated flow rate Pump speed Max Power

10 [ MPa ]9 [ dm3/min ]2800 [ r/min ]2 [ kW ]

Table 2.

Chemical and Physical properties

Base Gasoline BL2 CR30

Motor Octane Number (N.O.M.M.)

64

Density [ kg/dm3 ] 0.6776Lower Heating Value[ MJ/kg ]

44.83

Reid Vapour Pressure[ kPa ]

70.33

Sulphur [ ppm ] by vol. 4Olefins [ % ] by mass 1.2Naphthene [ % ] by mass 10.0ISO-Paraffin [ % ] by mass 40.2NOR-Paraffin [ % ] by mass 44.3Aromatic Tot. [ % ] by mass 4.3Aromatic Superior [ % ] by mass 0.7Aromatic Index 20.0Benzene [ % ] by mass 1.8Toluene [ % ] by mass 1.0Xilene [ % ] by mass 0.8

Table 3.

O.N. RESEARCH METOD s=0 s=0.5 s=1 s=1.25 s=1.5

CR30 "BL1"

34 42 50 - -

CR30 "BM1"

52 61 69 - -

CR30 "BL2"

70 77 87 91 95

CR30 "BL3"

73 81 90 - -

Fig. 2

Scheme of the modified intakepipe with water injector

7

0

5

10

15

20

25

30

35

40

45

50

55

60

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 660 690 720

crank angle [deg]

cylin

der

pres

sure

[bar

]

"s" = 1 "s" = 0

0

5

10

15

20

25

30

35

40

45

50

55

60

330 360 390 420 450 480

crank angle [deg]

cylin

der

pres

sure

[bar

]

"s" = 1 "s" = 0

Fig. 3

Effect of water injection over pressure traces ofCFR engine

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

V [cm3]

pres

sure

[bar

]

"s" = 0 "s" = 1 "s" = 0.5

CONSTANT VALUE OF VOLUMETRIC COMPRESSION RATIO 5.25

Fig. 4

Effect of water injection on the indicated pressure-volume diagram

0

10

20

30

40

50

60

240 300 360 420

crank angle [deg]

cylin

der

pre

ssur

e [b

ar]

"s"=0 r=5.25 "s"=0.6 r=5.74 "s"=1 r=6.28 "s"=1.25 r=7

Fig. 5

Effect of the water injection on pressure –crank angle diagram (fixed fuel U variable)

0

10

20

30

40

50

60

0 85 170 255 340 425 510 595 680 765

V [ cm3 ]

cylin

der

pres

sure

[ ba

r ]

"s" = 1 "s" = 0

Fig. 6

Effect of the water injection on thediagram area

Water injection effect on the anti-knock qualit y

50

60

70

80

90

100

0 0,25 0,5 0,75 1 1,25 1,5

Water / Fuel mass rati o

Oct

ane

Num

ber

N.O. M.M.

N.O. R.M.

Fig. 7

Effect of water content on the anti-knock qualityof water-gasoline combination

8

Water injection effects on exhaust temperatures

660

670

680

690

700

710

0 0.5 1 1.5

Water / Fuel mass ratio

Exh

aust

Tem

pera

ture

[ K ]

Fig. 8

Effect of water content on the exhausttemperatures of water-gasoline combination

Effect of water injection over NOx emissions

20

30

40

50

60

70

0 0,5 1 1,5

Water / Fuel mass ratio

NO

x [ p

pm ]

by v

ol

Fig. 9

Effect of water content on the NOx emissionsof water-gasoline combination

Fig. 10

Calculated pressures versus water / fuel massratio

0

5

10

15

20

25

30

35

40

330 335 340 345 350 355 360 365 370 375 380 385

crank angle [deg]

cylin

der

pres

sure

[ ba

r ]

"p" = 0,5

"p" = 1

"p" = 1,25

"p" = 1,5

Calulated unburned gas temperature

0

500

1000

1500

2000

330 340 350 360 370 380 390

crank angle [ deg ]

Tem

pera

ture

[ K

]

Tu calculated

Fig. 11

Temperature of the unburned mass fractionduring combustion development (“s” = 1.25)

00,20,40,60,8

11,21,41,61,8

0 0,5 1 1,5

Water / fuel mass ratio

Det

onat

ion

Inde

xIdet required Idet available

Fig. 12

Detonation Index “required” and “available”versus water / fuel mass ratio

-1 0 0

-8 0

-6 0

-4 0

-2 0

0

2 0

4 0

6 0

8 0

1 0 0

0 0 , 7 1 1 , 2 5 1 , 5

W ate r / fu e l m as s r a ti o

Ant

i kno

ckin

g m

argi

n

Fig. 13

Anti knocking margin versus water / fuelmass ratio

9

CONCLUSIONS

The development of SI- ICE has been accompanied bythe desire to raise the compression ratio for increasedengine efficiency and better fuel economy. One obstacleto this gain in the economy, at times, has been the octanequality of the available gasoline. To overcome this limita-tion, water was proposed by several authors as an anti-knock to suppress detonation. The information generatedduring these studies, under a variety of engine typologiesand running conditions, does not yield homogeneousresults.

In this paper water injection effects on a single cylinderCFR-SI engine have been investigated from both theoret-ical and experimental viewpoint. Tests were performed atAGIP Petroli Fuels Control Laboratories, Priolo (CT).

The primary effects of the examined water injection sys-tem were concerned with the utilisation of very low O.N.base gasoline (cheap products, intermediate of refineryprocesses) in SI-ICE, antiknock characteristics, detona-tion index, and exhaust emission.

Based on the experimental findings in engine fed withbase gasoline mixture and gasoline-water-air combina-tions, it is possible to conclude that:

1. Water injection system was tested on CFR engineaccording to Research and Motor methods (ASTM)in order to increase the antiknock rating of a virginnaphtha rated at 64 O.N.M.M (68 O.N.R.M.).

2. With regard to the tested base gasoline, by simulta-neously increase of volumetric compression ratio andwater injected mass flow rate, measured ResearchOctane number increases to 93 from 70 and MotorOctane number to 90 from 64.

At present the best results were obtained with waterinjection/fuel mass flow rate in the field over one ratio(1 < “s” ≤ 1.25) at standard engine spark advance.

3. Experimental data showed nitric oxide reductions ofover 50% with water injection/fuel ratio in the rangefrom 1 to 1.25 (1< “s ”< 1.25). Water injection causeda drop in carbon monoxide emission concentrations;this effect was more noticeable with rich mixture run-ning conditions where CO levels were relatively high.Conversely, water injection in amounts equal to thefuel flow caused about 20 % increase of hydrocarbonemissions in the exhaust gas.

4. Using both experimental p-V data and calculationsresults, a model that allows to determine detonationindex to predict water injection effects for a fixed fuel,while “s” was varied from 1.5 to 0, has been imple-mented. The comparison between required andavailable detonation index leads to the definition of asuitable anti knocking margin that allows to extendinvestigations to several low O.N. petrochemicalproducts.

ACKNOWLEDGEMENTS

The author gratefully acknowledges the collaborationgiven by Dr. P. Bernetti manager of Experimental FuelControl Station of AGIP Petroli, Priolo's Oil Refinery.

REFERENCES

1. Rave, M.R., "Water Injection for Aircraft Engines,"Trans.SAE, V.54,Nov.1946.

2. Obert, "Detonation and Internal Coolants," Quart. Trans.SAE, Jan. 1948, pp.52-59.

3. Johnson, R. T. "A Comparison of Gasoline, Methanol andMethanol/Water Blend as Spark Ignition Engine Fuels,"Paper presented at International Symposium on AlcoholFuel Technology , Wolfsburg, Fed. Rep. of Germany, 1977.

4. Nicholls, J. E. "Inlet Manifold Water Injection for Control ofNitrogen oxides - Theory and Experiment," Trans. SAE,paper 690018, 1969.

5. Bignardi , L. et. al. "Products of Combustion of Water inFuel Emulsion, " 14th International Congress on Combus-tion Engine, Paper D-98, Helsinki, 1981.

6. Satpov, E. B. and Luksho, B.A., " A Study on the Effect ofWater in Fuel on the Performance of SI Engine, " publishedin Engine Manufacturing in Russian, 1982.

7. R.Lanzafame, "Effetto dell'introduzione dell'acqua all'aspi-razione, sul comportamento di un MCI ad accensionecomandata, nei riguardi della detonazione, " Quadernidell'Istituto di Macchine , Università degli Studi di Catania,Marzo 1996.

8. R.Lanzafame, S.Mancò, "Effetto dell'iniezione d'acqua sulfunzionamento di un MCI ad accensione comandata, " 48°Congresso Nazionale ATI, Taormina 28 Settembre, 1Ottobre 1993.

9. F.Bassi, R.Lanzafame, A.Risitano, "Acetylene and water asfuels for spark ignition engine, " 26th Intersociety EnergyConversion Engineering Conference IECEC '91 - BostonMassachusetts, August 4-9-1991.

10. J.B.Heywood, "Internal Combustion Engine Fundamentals," MC Graw - Hill International Editions.

11. C.F. Taylor, " The Internal Combustion Engine in Theoryand Practice," vol.1,2.

12. A.Beccari - C.Caputo, " Motori Termici Volumetrici", Ediz-ioni UTET.

13. J.I.Ramos, "Internal Combustion Engine Modelling, " Hemi-sphere Publishing Corporation.

14. Livengood and Wu, "Correlation of auto-ignition phenom-ena in Internal Combustion Engines and Rapid Compres-sion Machine".

10

CONTACT

Prof. Ing. R. Lanzafame

University of Catania – Engineering Faculty - MachineryInstitute

Viale A. Doria 6 95125 Catania

Tel. +39 95 7382414

Fax +39 95 330258

e-mail: rlanzafa@im.ing.unict.it

NOMENCLATURE

s: water to fuel mass ratiom: total gas massmu: unburned gas massmb: burned gas massθ: crank angleV: total gas volumeVu: unburned gas volumeVb: burned gas volumeRu: unburned gas constantRb: burned gas constant

v: gas specific volumevu: unburned gas specific volumevb: burnedgas specific volumexb: gas mass burnt fractionhu: unburned gas specific enthalpyhb: burned gas specific enthalpyeu: unburned specific internal energyeb: burned specific internal energy

eu0: unburned specific internal energy of formation at the

reference temperature

eb0: burned specific internal energy of formation at the

reference temperaturep: cylinder pressureT: absolute temperaturet: time

: time delayn: engine speedIdet: detonation index

subscripts

u: unburnedb: burnedR: reactionCR: crevices

τ