Water injection in the normally-aspirated piston engine

TFCH^n^CHE HOGESCHOOL

ÜIGEOUWKUI'^DE Kanaalstraat iO - DELFT

31 Mffl[ ^^^-^

THE COLLEGE OF AERONAUTICS

CRANFIELD

WATER INJECTION IN THE NORMALLY-ASPIRATED

PISTON ENGINE

by

NOIE NO .78 March. 1957. T H E C O L L E G E O F A E R O N A U T I C S O R A N F I B L D Water I n j e c t i o n i n t h e N o r m a l l y - A s p i r a t e d P i s t o n Engine b y

-E.M. GOODGER, M . S c . ( E n g . ) , A.M.I.MeGh.E., A . P . R . A e . S . , P . I n s t . P e t ,

STO'WiRY

The i n j e c t i o n of Virater i n t o a s p a r k - i g n i t i o n p i s t o n engine t e n d s t o reduce b o t h t h e po\7er and t h e tendency t o k n o c k . Because of t h e l a t t e r e f f e c t , t h e c o n d i t i o n s of o p e r a t i o n can be made more s e v e r e i n o r d e r t o r e a l i s e o v e r a l l g a i n s i n power and economy.

I n j e c t i o n of w a t e r a t d i f f e r e n t p o i n t s i n a s i n g l e - c y l i n d e r e n g i n e shows t h e most p r a c t i c a b l e method t o bo f i n e a t o m i z a t i o n i n t o t h e i n l e t m a n i f o l d . ITater flow r e q u i r e m e n t s a r e found t o be d i r e c t l y p r o p o r t i o n a l t o t h e manifold a b s o l u t e p r e s s u r e , ejid a commercial t y p e of T/ater i n j e c t i o n u n i t d e s i g n e d on t h i s b a s i s i s d e s c r i b e d and r o a d - t e s t e d .

An attenrpt h a s b e e n made t o e s t i m a t e the d i s t r i b u t i o n of w a t e r t o i n d i v i d u a l c y l i n d e r s of a m u l t i - c y l i n d e r e n g i n e , and t h e e f f e c t of w a t e r up on e n g i n e components i s examined.

H T h i s n o t e i n c l u d e s r e s u l t s from a t h e s i s s u b m i t t e d by

L t , J . H, Dunphy, R . N , , i n J u n e 1955 ( r e f . 7 ) , a s p a r t of t h e r e q u i r e m e n t s f o r t h e award of the Diploma of t h e C o l l e g e of A e r o n a u t i c s . R e s u l t s a r e a l s o i n c l u d e d from a d d i t i o n a l work by J , H i l l s d o n ( r e f . 8 ) , t h e r e s e a r c h b e i n g u n d e r t h e s i i p e r v i s i o n

Introduction.

The use of water injection in internal-combustion engineering dates back to 1913, when Professor Hqpkinson injected water into a gas engine in order to cool the chamber walls (ref.l). A considerable reduction in thermodynamic efficiency was found, which indicated that the water had vaporised before reaching the walls and had reduced the activity of the burning gases. The

object of water injection today is, in fact, to cool the end-gas portion of the charge, rather than the chamber walls, but similar adverse effects upon performance may result unless the system is applied correctly.

The attraction of water injection lies in its suppression of knock. Under normal conditions of combustion, the spark-ignited flame propagates throughout the chamber producing a smooth rise in pressure. Dioring this process, the unbumed portion of the charge experiences the same pressvire rise and, in consequence, an

adiabatic rise in temperature. Under severe conditions of operation, the temperature of the unburned portion reaches the level for

spontaneous ignition, and the end-gases ignite and b u m at a very rapid rate. This phenomenon is termed knock, and its occiorrence depends largely upon the temperature level within the chamber, and the spontaneous-ignition characteristics of the charge at the normal peak chamber pressure. Improved cooling of the end-gas zone of the chamber, either externally or internally, widens the gap between the two temperature levels, and so delays the onset of knock.

A recognised anti-knock practice in spark-ignition piston engines is to use the fuel itself as an internal coolant, by employing an over-rich mixture under extreme power conditions. Water appears more attractive as a knock suppressant in view of

its negligible cost and higher thermal capacity. The reduction in power occasioned by the injection of water must be offset, and

outweighed, by an increase in the severity of operating conditions, so that overall gains in performance result.

An a d d i t i o n a l advantage claimed for vrater i n j e c t i o n i s the more complete combustion of the carbon content of the fu.ol, the r e a c t i o n between hot aarbon. and vra-ter r e s u l t i n g i n gaseous carbon monoxide and hydrogen. This tends to minimise the formation of carbon d e p o s i t s , and extend the periods between top overhauls.

2 . Effects of Tfater Upon Engine Performance. 2,1 . Humidity and Air Temperature.

Some water vapour i s normally present i n atmospheric a i r , and the amount of viratcr capable of existence i n the vapour phase depends upon both temperature and p r e s s u r e . Relative humidity i s expressed on a percentage b a s i s , derived from the mass r a t i o of water vapour a c t u a l l y present i n u n i t volume of moist a i r to t h a t which would be iDret^ent a t f u l l s a t u r a t i o n . In h o t , moist, c l i m a t e s , a maximum r e l a t i v e humidity of about 90^ i s found a t an a i r

temperatiire of about 40 C . , which represents a water vapoior

content of 0.044 I b . / l b . dry a i r . Water vapour displaces dry a i r , so t h a t a given vol-ume of t h i s moist a i r contains only 9 3 . ^ of the mass of dry a i r occupying the same volume. (See r c f s . 2 and 3 ) .

I n g e n e r a l , the po\-vor output of a s p a r k - i g n i t i o n engine i s d i r e c t l y dependent upon the mass throughput of dry a i r . Since the swept voli:une i s f i x e d , operation a t constant temperature and v a r i a b l e humidity can be assumed to incvir a constant volume

throughput of moist a i r . The value 93»^°) t h e r e f o r e , represents the reduced power a y a i l a b l e due to a r e l a t i v e humidity of 90^ a t 40 C . , and f i g . 1 shows hov7 the povrer v a r i e s vnLth v/ater vapoixr mass concentration,

I n a s i m i l a r way, assuming a constant volume throughput, the power v a r i e s i n v e r s e l y with the intake a i r absolute temperature, as shown i n f i g . 2 .

2.2, Induction and Combustion Processes.

The individual effects of water introduced into the induction manifold of a spark-ignition piston engine are illustrated in the following table :-TABLE 1 . Stage Induction Compression 1 Stroke Power Stroke 1 (mean flcone) Pwvur Stroke (end-gas zone) Process

Vaporisation cools mixture u n t i l a i r s a t u r a t e d .

F u r t h e r vaporisation cools charge and reduces work of compression. Vaporisation, and presence

of vapour, both reduce flame speed, and hence r a t e of pressure r i s e . Vaporisation, and vapoiir,

cool end gases and r a i s e s l i g h t l y t h e i r spontan-e o u s - i g n i t i o n tspontan-empspontan-eraturspontan-e. Effect on Performance 1 Pov/er increased by 1 cooling u n t i l s a t u r a t i o n , then 1 decreased by a i r | displa-cement. Pov/er increased. 1

1

Inspection of the above table suggests that, with low rates of water flov/, the twj initial effects would produce a slight overall increment in power output. At higher rates of v/atcr flow, the

reduced flame speed could be expected to reverse the first beneficial effect and outweigh the second, so that a progressive loss of

3.

The introduction of v/ater a t d i f f e r e n t p o i n t s i n the engine airflow system should help to c l a r i f y the r e l a t i v e magnitude of the. e f f e c t s shown i n Table 1 . The Pedden s i n g l e - c y l i n d e r sleeve-valve engine (see Appendix) v\ras t e s t e d a t constant conditions of

2,500 r . p . m . , f u l l t h r o t t l e , 15 i g n i t i o n advance, and maximum power mixture (approx. 12/1 A / P ) , vising an Argus c a r b u r e t t o r . Water was i n j e c t e d using four d i f f e r e n t methods, v i z :

-A, Continuous i n j e c t i o n upstream of c a r b u r e t t o r ) i n l e t B. Timed i n j e c t i o n i n t o i n l e t p o r t J C. I n j e c t i o n during compression stroke"^ Gonbu'^tion •n X • 4.- J • 4. 1 \ Chamber D, I n j e c t i o n during pov/er stroke J

Additional t e s t s v/ere then conducted to determine the e f f e c t of i n j e c t e d v/ater upon kiiock-limited power.

3.1 . Continuous I n j e c t i o n Upstream of Ca.rburettor.

Water from an overhead supply tank v/as passed through an edge f i l t e r i n t o a Siemens gear-type pump running a t 800 r.p.m. I n order t o obtain a f i n e l y - d i v i d e d v/ater spray i n the manifold, the water was fed through an u p r i s e r pipe i n t o a ' scent-spray' atomiser, using an atomising a i r pressure of 10 p . s . i . g . ( P i g s . 3 and 4 ) .

Interchangeable atomiser caps of d i f f e r e n t o r i f i c e diameters v/ere a v a i l a b l e i n order t o obtain a vri.de range of v/ater flow ( i . e . to siiit both a s i n g l e - and a m u l t i - c y l i n d e r engine) for a given range of water pressure from zero to 250 p . s . i . g . A 50 ml. bulb v/as used to determine the water flow r a t e . The v a r i a t i o n s with water flow i n power, specific f u e l consuniption, and s p e c i f i c l i q u i d consumption are shown i n P i g s . 5 , 6 , 7 and 8 .

The shape of the power curve i n P i g . 5 confirms the conclusions i n p a r a . 2,2 regarding the r e l a t i v e significance of the individioal e f f e c t s of v/ater on the processes of induction and combustion,

The lower ovjrve i n P i g . 5 i l l u s t r a t e s the reduction i n power caused by an increase i n humidity, as outlined i n p a r a . 2 , 1 .

3 , 2 . Timed I n j e c t i o n , i n t o I n l e t P o r t .

The Pedden engines v/ere designed to operate with an Excello low-pressiu:^ (30 p . s . i . g . ) timed fuel i n j e c t i o n system, and one of the Excello spring-loaded i n j e c t o r s was used to spray water i n t o the c e n t r a l i n l e t p o r t of the Pedden single-cy].inder engine. An Argus c a r b u r e t t o r was used for the f u e l supply. The v/ater was pxirnped on a timed b a s i s by means of an enginedriven Bryce s i n g l e -element d i e s e l - t y p e fuel pump. I n order to minimise corrosion i n the system due t o the passage of v/ater, an o i l tank and tv/o-way cock were incorporated i n the v/atcr system, and an Ensis type v/ater-repelling o i l was fed i n t o the p-uinp a t the beginning and end of each t e s t . The sleeve i n l e t p o r t opened from 15 before top dead centre to 55 a f t e r bottom dead c e n t r e , and i n j e c t i o n of v/ater v/as timed to commence a t 20 a f t e r top dead centre on the induction s t r o k e . Results are included i n P i g s . 6, 7 and 8,

3'3' Iri^jcction During Compression S t r o k e .

The same Bxyce pump and v/ater system v/ere employed, feeding to a B,M,W, 801 injectoi', operating a t 500 p , s . i , g , , f i t t e d i n t o the cylinder head. I n j e c t i o n commenced a t 55 a f t e r bottom dead c e n t r e , i , e , a t the i n s t a n t of closure of the i n l e t p o r t . Results arc shown i n P i g s . 6, 7 ar.d 8 .

3 . 4 . I n j e c t i o n Drg-'ing Pov/er Stroke .

Using the same equipment, the v/ater i n j e c t i o n timing v/as

r e t a r d e d t o commence a t top dead centi-e on the power s t r o k e . Results are included i n P i g s . 6, 7 and 8 ,

3,5» Comparison o_f R e s u l t s ,

The power curves i n P i g , 6 show c l e a r l y t h a t the most e f f e c t i v e system of water i n j e c t i o n i s method B, i n v/hich the v/ater i s i n j e c t e d through the i n l e t x^ort on a timed b a s i s . Although l e s s time i s

7

-available for a ' supercharging' effect due to vaporisation and charge cooling, the injected v/ater is introduced into the chamber in a

positive manner, and does not displace the manifold air,

Corarespending variations are seen to occur in the specific fuel consumption (Pig. 7 ) . The curves in Pig. 8 indicate the extent of the price to be paid, in terms of the total consumption of liquids, for the advantages gained when using water injection,

Despite these optiinum results for method B, it can be

concluded that the continuous manifold injection system of method A is more suitable, since this does not require the provision of a high-precision timed injection system, nor of oil-addition to prevent corrosion of the pump or injector. The slight increase in pov/er at lew water flcaTS is accexatable, but not of siofficient magnitude in itself to v/arrant the additional complication of a water injection system,

3«6, lüiock-Limited Power Tests.

The real value of water injection lies in its suppression of knock, and in the possibility of opera^ting at severe conditions which otherwise v/ould be prohibited. Increases in severity, in the

form of greater ignition advance or higlier coinprecsion ratio, lead to iirrproved power and economy. Tests were conducted, using the continuous manifold injection system (method A) in the P,K,P,S. single-cylinder variable-compression engine, v/ith the ignition advanced to incipient knock at \'arious rates of water flow. The knock-limited pov/er cixrve is shov/n in Pig, 9A together with various falling pov/cr ciorves obtained at constant values of ignition advance, The figure shows an increase of 10.6^ pov/er to be obtainable by

means of an advance in ignition from 8 to 4'! before top dead centre, v/ith a v/ater/fuel mass ratio of about 1,5, Water/fuel mass ratios in excess of 1,5 led to unstable operation,

Further tests were conducted vdth the compression ratio increased to incipient knock at various rates of ^vater flov/. The results in

F i g , 513 shoT/ an increa^se of 4 . 6 ^ iDOwer obtained from an increase i n coirprcssion r a t i o from 6,4/1 t o 8/I , m t h a v/ater/fuel mass r a t i o of about 1,5, The cruves i n P i g , 9C show s i m i l a r reductions i n sïpecific f u e l consumption (of approx, 1C^) v/hen i g n i t i o n timing and conipression r a t i o are increased sepaxately to maintain an i n c i p i e n t knock condition v/ith the i n j e c t i o n of v/ater. These compare v/ith the increase i n s p e c i f i c fuel consumption of over 4 ( ^ t h a t r e s u l t e d v/hen v/ater v/as i n j e c t e d v/ithout advancing i g n i t i o n to i n c i p i e n t knock. Increases i n s p e c i f i c l i q u i d

consumption of about 10C^ v/cre incurred i n each c a s e , v/hich compare v/ith an increase of about 30C^ when i g n i t i o n advance remained c o n s t a n t , 4 . P r a c t i c a l Systems.

The grea-test tencbncies t o knock are found a t f u l l t h r o t t l e and lew engine speeds, v^ere the chamber pressure i s high, and the tinx3 available for spontaneous i g n i t i o n i s long, A change i n engine speed a t constant t h r o t t l e p o s i t i o n gives r i s e to a change i n the manifold p r e s s u r e , A system of water i n j e c t i o n i n t o the intake manifold, t h e r e f o r e , should be c o n t r o l l e d so t h a t the v/ater flov/ i s d i r e c t l y p r o p o r t i o n a l to the manifold absolute p r e s s u r e , i , e , maximum v/ater supplied a t low ma.nifold dep3ression, I t should a l s o ensure t h a t no v/atcr flOT7 i s p o s s i b l e v/hen the engine i s shut dov/n, i . e , zero water supplied a t zero manifold depression ( P i g , I O ) . These tv/o requirements almost c o n f l i c t , and tv/o c o n t r o l devices may be n e c e s s a i y ,

In one commercially-developed system, ( r e f , 4 ) , the writer i s introduced i n t o the manifold, on the engine side of the t h r o t t l e , under the a c t i o n of the manifold depression ( F i g , 1 1 ) , The inverse r e l a t i o n s h i p betv/een manifold depression and v/ater flew i s obtained

K Interconiparison betv/een the tv/o s e t s of r e s u l t s ( P i g s , 9A and 9 B ) may not be made d i r e c t l y since some engine maintenance v/ork effected betv/een the tvvo t e s t s v/a.s found to have influenced the performance l e v e l ,

9

-by allowing tlie manifold pressure t o a c t upon a spring-loaded diaphragm and j e t d e v i c e . Reduced dejpression allov/s the sioring t o x^ush the j e t away from a fixed "inverse-flov/" n e e d l e , and so increase the flow. The manifold pressure reaches a mxlmum v a l u e , equal t o atmospheric p r e s s u r e , when the engine i s shut down. Since the inverse-flov/ j o t i s then f u l l y oxxsn, a second needle i s inooi.-porated i n order to cut off the suxox^ly of v/ater. The cut-off needle i s a l s o connected t o the diaxohragm, and i s arranged t o close by the action of the diaphragm s p r i n g . Manual c o n t r o l s are f i t t e d so t h a t the water flov/ may be adjusted to s u i t the engine and driving c o n d i t i o n s ,

I n an a l t e r n a t i v e system, developed i n America, (Ref, 3) > the i n j e c t i o n device i s v i r t u a l l y a c a r b u r e t t o r , complete with f l o a t chamber ( P i g , 1 2 ) . The leaded alcohol-v/ater f l u i d i s delivered i n t o the Trenturi of the main carb^arettor, under the

action of the v e n t u r i depression. Since the ventinri pressiire bears an inverse r e l a t i o n s h i p v/ith the manifold p r e s s u r e , changes i n t h r o t t l e p o s i t i o n a t constant engine sjseed cause the f l u i d flow t o vary d i r e c t l y with the venturi dex^ressffion, and no inverse-fl(3v/ needle i s required. However, t h i s gives a l e s s s e n s i t i v e c o n t r o l

of f l u i d for engine sjjeed a t constant t h r o t t l e p o s i t i o n , and a passage (shov/n dotted) i s l e d from the diaphragm chamber to the v e n t u r i tube i n order t o improve t h i s s e n s i t i v i t y ,

4.1 , Water D i s t r i b u t i o n t o Individual Cylinders.

The successful a p p l i c a t i o n of any system i n v/hich f l u i d i s introduced i n t o the manifold of a m u l t i - c y l i n d e r engine dexoends upon the uniformity of d i s t r i b u t i o n of the f l u i d to the i n d i v i d u a l c y l i n d e r s . Performance sioffers markedly i f the fuel i s badly d i s t r i b u t e d , and s i m i l a r probleins a r i s e when water or other manifold-injected f l u i d s are employed.

Since the mean temperature of the chamber gases reduces progressively with increase i n v/ater flov/, t h i s temperature was

i n v e s t i g a t e d v/ith a view to i t s use as a q u a n t i t a t i v e i n d i c a t i o n of water flov/ r a t e t o the c y l i n d e r . The Pedden s i n g l e - c y l i n d e r

engine was \ised i n order t o obtain the tempera.ture-flow r e l a t i o n s h i p , and t h i s curve v/as then employed as a c a l i b r a t i o n of water flow

r a t e t o the i n d i v i d u a l c y l i n d e r s of the Pedden f l a t - s i x engine, The s i x cylinders of the l a t t e r engine are of the same design and dimensions as t h a t f i t t e d to the s i n g l e - c y l i n d e r engine,

A thermocouple i s incorporated i n the head of the Pedden s i n g l e - c y l i n d e r engine as a standard f i t m e n t , and the v a r i a t i o n s i n temperature with water flov/ are shov/n i n P i g , 1 3 , The curves follcw the general trends shov/n by the pov/er curves i n F i g , 6, In order to increase s e n s i t i v i t y , and hence accura.cy, a thermo-couple-type sjjai-king plug v/as f i t t e d and the mean temperature a t the t i p of the c e n t r a l e l e c t r o d e vra.s measured. The temperature-flow c a l i b r a t i o n curve obtained using i n j e c t i o n method A , i s

shown i n P i g , 14. After an i n i t i a l s l i g h t c u r v a t u r e , the r e l a t i o n -shix^ i s almost l i n e a r , and the c a l i b r a t i o n appears t o be s a t i s f a c t o r y for a p p l i c a t i o n to the f l a t - s i x engine,

The ' scent-spray' water atomiser u n i t was f i t t e d onto the i n l e t of the Argus carbui-ettor feeding the manifold of the f l a t - s i x engine, as shov/n i n P i g s , 15A and B, The Argus c a r b u r e t t o r had been f i t t e d f o r eai-lier t e s t s on fuel d i s t r i b u t i o n b u t , for the water d i s t r i b u t i o n t e s t s , the f u e l was sux^plied by means of the standard Excello p o r t - i n j e c t i o n system, and the cajrburettor wa.s not used. The engine was run a t 2500 r . p , m . and 15 i g n i t i o n advance, v/ith a constant f u e l consumption. Individual cylinder temperatures v/erc measured by means of theirmocouple sparking p l u g s , The engine c o n s i s t s e s s e n t i a l l y of tvo t h r e e - c y l i n d e r i m i t s mounted back to back, and the v/ater d i s t r i b u t i o n p a t t e r n s v/ere t o be based

on the two banks s e p a r a t e l y , i , e , cylinders 1 , 3 » and 5» and cylinders 2 , 4 and 6 .

The engine x^rfonnance v/as not quite up to standard v^ien the i n i t i a l water d i s t r i b u t i o n t e s t s vrare conducted, due mainly t o f a u l t s

l i

-on tlae fuel system and i n the thermocouple leads from cylinders 1 and 2 , but the r e s u l t s are presented a.s an i n d i c a t i o n of tlae order of difference between i n d i v i d u a l flows. F i g s , 16 and 17 show the tenTperature v a r i a t i o n and the deduced water flows r e s p e c t i v e l y , f o r cylinders 1 , 3 ajid 5 only. I f cylinder 1 i s disregarded, i n view of the themiocoux^le lead f a u l t s , the v/a.ter appears to have t r a v e r s e d to the end of the s t r a i g h t rake manifold, and t o have supplied cylinder 5 v/ith a g r e a t e r shasre. However, the r e s u l t s are too meagre for d e f i n i t e conclusions to be drav/n,

h-<>2. Effect, of Water on Engine Components,

On completion of the water i n j e c t i o n t e s t s i n the s i n g l e -c y l i n d e r engine, the engine v/as strix^xtied and examined for signs of corrosion and d e p o s i t s . In order t o minimise the p o s s i b i l i t i e s of c o r r o s i o n , the engine had been run f o r five minutes a t the end of each t e s t ai'ter the i n j e c t i o n of v/ater had ceased, during vAaich tiffiC the Bryce pump was fed with Ensis o i l . The t o t a l rxinning time of 400 hours included 20 hoiors with v/ater i n j e c t i o n i n ox^eration. The condition of the engine components shown i n

P i g , 18 was considered to be normal, and no signs of corrosion v/ere apparent. The carbon deposits v/ere as expected, and the i n j e c t e d water did not appear t o have had any great e f f e c t upon the e x i s t i n g

carbon which must have b u i l t up before the t e s t s v/ere commenced, The Bryce pump coiiiponents are shown i n F i g . 19. No evidence of corrosion v/as ajjparent, nor any damage t o the precision-grovtnd plunger and b a r r e l .

4 . 3 . Engine Road T e s t s .

Some preliminary roaxl t e s t s v/ere conducted i n a pre-war car with a four-cylinder 10 h . p . engine f i t t e d with the commercial water i n j e c t i o n u n i t of E i g . 1 1 . An on-off cock v/as incorporated

i n the v/ater d e l i v e r y l i n e so t h a t the system coiold be i s o l a t e d . A vacuoim gauge v/as a,lso f i t t e d , and a maximum manifold depression of 8 p . s , i , g , was noted under i d l i n g c o n d i t i o n s ,

With c u r r e n t (1955/56) motor f u e l s , a range of octane r a t i n g (motor ncthod) of about 72 t o 82 was considered t o be a v a i l a b l e , from r e g u l a r t o premium gra.des. The difference i n s e v e r i t y between optimum conditions for the two fox; I s i s not as v/ide as t h a t

represented i n F i g , 9, and a v/atcr/fuel volvimc r a t i o of about 0,4 was estimated a.3 the probable maximum. Since, i n x^ractice, knocking conditions are encountered f o r a f r a c t i o n only of driving time, and since t h i s v/ould represent no more than about 2C^ of the t o t a l f u e l consiiqption, the o v e r a l l w a t e r / f u e l voliime r a t i o on the road would be expected not t o exceed about 0,08, i , e . approximately 1 gallon of water to 12 gallons of g a s o l i n e , or a consojmption of 1 p i n t of v/ater p e r 50 m i l e s .

The engine was operated i n i t i a l l y v/ith premium-grade gasoline a t optimum i g n i t i o n and mixture. Regular-grade gasoline vTas used. n e x t , a t the same engine c o n d i t i o n s , and knock was experienced under

a c c e l e r a t i o n and h i l l - c l i i o b i n g . Water was introduced, and the flow r a t e adjusted to eliminate knock under the same conditions of

a c c e l e r a t i o n and h i l l - c l i m b i n g , A water consimiption of 1 p i n t p e r 50 miles v/as found to represent a f a i r average a t t h i s s e t t i n g . Increased water flow gave a noticeable power l o s s , and a reduced water flc^w l e d to trace laaock.

The f u e l mixture was not v/eakened when water i n j e c t i o n was i n operation, but some slifiht iiiiprovt3mont i n econowy was noted, Fuel consumption v/as recorded duiung consecutive periods with and vrithout v/atcr, the t o t a l mileage i n each case being about 800 m i l e s . Average values of 25.0 and 23.0 m,p,g, resx^ectively were

obtained, i , e , an improvement i n econoniy of 8,7?5, A top overhaul a t the conclusion of the t e s t s revealed a marked reduction i n the extent of carbon dex^osits. Normal mains water was used throughout the t e s t s , and a tendency t o j e t blockage was noted occasionally,

13

-5 , Alternative I n j e c t i o n Fluid.s,

For operation under cold v/ea.ther conditions, some form of f r o s t p r o t e c t i o n i s required f o r the v/ator i n j e c t i o n system, and

the e f f e c t s on the engine of the a n t i - f r e e z e agents must be

considered. The proxoerties of some p o s s i b l e ajiti-freeze materials are x^resented i n Table 2 , together v/ith the p r o p e r t i e s of water and of a iyx)ioal motor gasolirae. The effectiveness of v/ater as an i n t e r n a l coolant i n comparison with g a s o l i n e , i s brought out by the r e l a t i v e values of l a t e n t h e a t . I n a d d i t i o n , the s p e c i f i c heat of water i s roughly twice t h a t of a l l the other l i q u i d s shovm. The conventional a n t i - f r e e z e m a t e r i a l , ethylene g l y c o l , i s only about one t h i r d as e f f e c t i v e a heat absorber as v/ater, v/hereas methanol i s about one half as e f f e c t i v e as w a t e r . In a d d i t i o n , the methanol contained i n a wa.ter-methanol blend w i l l a c t as a blending agent i n the f u e l , and give a s l i g h t trend tov/ards improved anti-knock q u a l i t y . Alcohols a r e , t h e r e f o r e , the recommended a n t i - f r e e z e agents for v/ater i n j e c t i o n systems, and the freezing p o i n t s of water-alcohol blends are shov/n i n F i g . 20. Domestic methylated s p i r i t s contr^in axoproximately Sjfo of mixed a l c o h o l s .

6. Conclusj.ons.

1, Water vapour displaces dry air v/hen it enters the atmosphere, so that a reduction occurs in the mass flow rate of dry air v/hen an engine operates v/ith humid air. Increased humidity, therefore, leads to a reduction in engine pov/er,

2, Increa-sed air temperature reduces the mass flov/ rate of dry air, and leads to a reduction in engine pov/er,

3, Injection of water into the manifold air of a spark-ignition piston engine leads to an initial slight rise in pov/er due to the cooling effect on the charge resulting from vaporisation, and to the reduction in the work of compression,

4, TiThen the manifold air has become saturated, the engine pov/er drops with increased ra tes of water flow due to displaceiTient of dry

a i r by the water vapour, and to the i n h i b i t i n g e f f e c t of the water upon the speed of flame propagation,

5 . A maximum vKxter/fuel ma.ss r a t i o of about 1 ,5 i s obtainable before the onset of imstable operation due to 'drov/n out' of the

sparking p l u g s . v 6. The reduced power output r e s u l t i n g from extensive v/ater

i n j e c t i o n leads to a lower chamber temperature and a reduced tendency to knock.

7 . The cooling e f f e c t of v/ater i n j e c t i o n upon the end gases, and the s l i g h t increase i n t h e i r spontaneous-ignition temperatiore due t o the pjresence of v/ater vapour, lead t o a reduced tendency t o knock a t more severe conditions of operation, so t h a t an o v e r a l l power improvement can be r e a l i s e d .

8 . By maintaining a condition of i n c i p i e n t knock, an improvement i n pcT.'/er of about 1C^ i s obtainable v/ith i g n i t i o n advanced over a wide range, and of about &fo v/ith compression r a t i o increased from 6.4/1 to 8 / 1 .

9 . By maintaining a condition of i n c i p i e n t laaock, f u e l economy can be inproved by about 1C^.

10. The presence i n the charober of a d d i t i o n a l v/ater vapour tends t o i n h i b i t fiorther carbon deposition, b u t not t o a.ffect e x i s t i n g d e p o s i t s .

1 1 , Alcohols are considered to be s u i t a b l e a n t i - f r e e z e agents for water i n j e c t i o n systems.

15

-^iËSL?,^„^.J£C^Ë£SS_9JLi^i^^^ïSE.

.FLUiig...

mTERIA L T y p i c a l Motor G a s o l i n e Water E t h y l e n e G l y c o l Methanol E t h a n o l

CHi'iRGF; COOLING PROPERTIES

BOILING POINT °C 35 t o f?00 100 197.5 64.5 78.3 LATEl^r fIE/.T C a l . / g m . 70 539.3 191 263 201 AÏITI-JaJOCK PROPERTIES AUTOGENOUS-IGNITION Temp, ° C . (A .S.T.M. D28é-30) 315 "^ -436 * 489 *" 439 * OCTANE NO. MOTOR METHOD 73 -•m 98 99 K Ref. 6

References

1. HOPICENSON, B., Proc, I,Mech.E,, July, 1913, p,679. •

2. SL/iDE, H,Y>r,, "The Effect of Humidity on Piston Engine Performance", Shell Aviation News, September, 1947.

3. BOUCHARD, C.L., "Variables affecting Flame Speed in the Otto Cycle Engine". SoA.E. Journal 1937, p.514.

4. AIJON. "Experiences with the HpO Bomb". The Autocar, 8th October, 1954.

5. COLTfELL, A.T., "Nev/Economy added to Antidetenant" . S.A.E. Journal, Vol.58, March 1950.

6. GOODGER, E,M., "Spontaneous-Ignition Data of Hydrocarbons and Aviation Fluids" , College of Aeronautics Note No, 68, October, 1957.

7. DUNPHY, J,H,, "The Effects of Mixture Distribution and Water Injection upon Piston Engine Performance" .

College of Aeronautics Unpublished Thesis, June, 1955,

8. HITiSDON, J, Unpublished work. College of Aeronautics, October, 1957.

17 -APPENDIX ENGINE DATA ITTO^ Bore m,m. S t r o k e m.m, C R . Swept Volume C . C . I g n i t i o n F u e l M e t e r i n g if'EDDEN SINGLE 101.6 95.3 8/1 773 Magtaeto Two P l u g s Argus C a r b u r e t t o r o r E x c e l l o p o r t i n j e c t i o n

i'EDDEN FLTiT SIX

101,6 95.3 8/1 4638 Magneto Two p l u g s / c y l , A r g u s C a r b u r e t t o r o r E x c e l l o p o r t i n j e c t i o n P . K . F . S . 100 130 4 . 5 / 1 t o 25/1 1020 Magneto One p l u g P o r t I n j e c t i o n

i

o o - 0 2 0 0 4 Ib WATER VAPOUR/Ib DRY AIR

FIG. I. EFFECT OF HUMIDITY ON ENGINE POWER

g I05 100 95 o n \

V

N

WATER TANK I A « SCENT-SPRAY ATOMISER B » B.M.W. INJECTOR E « EXCELIJO INJECTOR P - PRESSURE GAUGE S e SPARKING PLUG C <• ARGUS CARBURETTOR GEAR PUMP

FIG. 3. WATER-INJECTION SYSTEMS USED ON FEDDEN SINGLE-CYLINDER ENGINE

FIG. 4. FINELY- DIVIDED SPRAY PRODUCED BY SCENT-SPRAY ATOMISER AT lOO P s.i.g. WATER PRESSURE

17-4 17-4 16-2 ^ < < " • cd Al. s A2 = '^^ MANIFOLD MANIFOLD INJECTION INJECTION ^ AT 4 2 % AT 6 3 % RELATIVE RELATIVE ' ^ - - , HUMIDITY ^ ^ HUMIDITY ^ ^ ^ - ^ ^ - . , 6 8 WATER FLOW 10 LB/HR

FEDDEN StNGLE-CYLINDER ENGINE, FULL THROTTLE, 2 5 0 0 R . P . M . , MAXIMUM POWER MIXTURE, I S ' IGNITION ADVANCE, 7 3 AVGAS. ( R E F . 7 . )

FIG. 5. EFFECT OF MANIFOLD WATER INJECTION AND HUMIDITY ON ENGINE POWER.

o

A - MANIFOLD INJECTION B ' PORT INJECTION

C = CHAMBER INJECTION ^COMPRESSION) O » CHAMBER INJECTION ( P O W E R )

O S I O WATER / F U E L M A S S RATIO

FEDOEN SINGLE-CYLINDER ENGINE CONDITIONS AS IN FIG.S (REF. 7)

FIG. 6 . EFFECT OF WATER INJECTION METHOD ON ENGINE POWER

0 - 6 8

WATER/FUEL MASS RATIO

FEDOEN SINGLE CYLINDER ENGINE CONDITIONS AS IN F I G . S . ( R E F . 7.)

FIG. 7. EFFECT OF WATER INJECTION METHOD ON SPECIFIC FUEL CONSUMPTION

I - 6 1 - 4 5 | . 2 a'

I

'" V^

w

FEDDEN S I N G L E - C Y L I N D E R ENGINE CONDITIONS AS IN F I G . S

l - S

(REF. 7 ) FIG. 8 . EFFECT OF WATER INJECTION METHOD ON

WATER/FUEL MASS RATK3

F.K.F.S. ENGINE, FULL TMfiOTTUE, HOO R. P.M., MAXIMUM POWER MIXTURE, 73 WGA5, WATER INJECTION METHOD A. ( R E F , B )

FIG. 9c ECONOMY CURVES

FIG. 9 . EFFECT OF WATER INJECTION ON POWER > ECONOMY WITH VARIABLE IGNITION TIMING AND COMPRESSION R A T I O .

MANIFOLD PRESURE > ATMOSPHERK

•^ MANIFOLD DEPRESSION

THROTTLE THROTTLE

OPEN CLOSED

F I G . I O . WATER FLOW REQUIREMENTS

AIR MANUAL CONTROL MANIFOLD DEPRESSION INVERSE FLOW NEEDLE

FIG. I I . DIAGRAMMATIC REPRESENTATION OF A COMMERCIAL WATER INJECTION UNIT

AIR

MANIFOLD DEPRESSION

FIG. 12. DIAGRAMMATIC REPRESENTATION OF AN AMERICAN FLUID INJECTION UNIT.

140 I 3 0 c I20 too 9 0 ^ ^ ^ \ \ \ \ \ \ y . B s > \ \ \ - ^

r^

V

FEDDEN SINGLE CYLINDER ENGINE CONDITIONS AS IN FIG. 5. ( R E F . 7.)

FIG. 13. VARIATION OF CYLINDER HEAD TEMPERATURE WITH WATER FLOW

5 2 0 50 O •c 4 8 0 4 » 0 4 4 0 4 2 0 MANIFOL \

X

1

FEDOEN SINGLE CYLINDER ENGINE CONDITIONS AS IN FIG.S. ( R E F . 7^

FIG. 14. VARIATION OF THERMOCOUPLE SPARKING-PLUG MEAN TEMPERATURE WITH WATER FLOW

FUEL FUEL CARBURETTOR (NOT IN USE)

_J^j>^-AIR

FIG. I 5 a DIAGRAMMATIC LAYOUT OF FEDDEN FLAT- SIX MANIFOLD

FIG. 15b. THE FEDDEN FLAT-SIX ENGINE EQUIPPED FOR WATER DISTRIBUTION TESTS

4 0 0 3SO "c 3 0 0 2SO 2 0 O

t

OVERALL WATER FLOW Ib/hr

FEDDEN FLAT-SIX ENGINE CONDITIONS AS IN F I G . S . ( R E F . 7 )

FIG. 16. VARIATION OF INDIVIDUAL CYLINDER TEMPERATURE WITH OVERALL WATER FLOW

1-3

UNIFORM WATER FLOW Ib/hr

4 I 6 I 8 10

I t I ; I

OVERALL WCTER FLOW Ib/hr.

FEDOEN FLAT-SIX ENGINE CONDITIONS AS IN FIG. 5 . ( R E F . 7 . )

FIG. 17. VARIATION OF WATER DISTRIBUTION WITH OVERALL WATER FLOW

FEDDEN SINGLE CYLINDER ENGINE

FIG. 18. ENGINE COMPONENTS AT CONCLUSION OF WATER - INJECTION TESTS.

FIG, 19. F U E L - PUMP COMPONENTS AT CONCLUSION OF WATER INJECTION T E S T S .

- I O ff

it!

\ ^ 1

s

V

M^

5 0 60