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https://ntrs.nasa.gov/search.jsp?R=19930081220 2020-03-03T00:24:33+00:00Z

NATICNAL ADVISORY COIMITTEE YOR AERONAUTICS——

TECHNICAL NOTE NO. 382

——

BASIC REQUIREMENTS OY 17UEL-INJECTION NOZZLES

FOR QUIESCENT. COMBUSTIOI? CHAMBERS

.

By J. A.. Spanogle and Ii.”H..Foster.

Summary

This report presents test results obtained at the LangleyMemorial Aeronautical Laboratory of the Natiorial Advisory Com-mittee for Aeronautics during an investigation of the performa-nce of a single-cylinder’, high-speed, compression-ignitiontest engine wheti using multiple-orifice fuel-injection valvenozzles in which the nufiber and the direction of the orificeswere varied independently. The orifice sizes generally con-formed to the principle that the orifice area should be pro-portional to the volume of air served by the orifice.

The test results indicate that it is unnecessary to followthe proportional principlq to’ extremes and that complication ofnozzle design does not give a commensurate increase in perform-ance. The optimum angle between orifice axes was jtidged to be25° for the conditions i.n this quiescent combustion chamber, butthis value “is not c“ritical.

.,

Introduction

In the course of the general program for the investigationand development of the high-speed, compression-ignition, fuel-injection engine as a power plant for aircrafts the staff ‘f . ~the Langley Memorial Aeronautical Laboratory has been &eter-mining the performance of a single-cylinder test engine with a

. vertiical disk-shaped combustion chamber in a cylinder head,desi nated in the test series N.A.C.A. cylinder head Nom 4.

“c

The combustion chamber ‘in this cylinder head is consideredquiescent because there is no evidence that the movement of theair in the combustion chamber has”’any effect on the distributionof fuel. Various multiple-orifice injection-valve nozzles havebeen use for introducing the fuel into the combustion chamber,and former- tssts as repor”ted- in”N.A;C.A”. Technical Note No, 344

R (Reference 1) indicated that for this type of combustion-chamberthe area of each orifice in a nultiple-ori.fice nozzle should be-proportional to the volume of air it served.#

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2 N.A. C.A. Technical Note No. 382

The forced air flow in this quiescent combustion chamberduring injection of the fuel is of such a low velocity that ithas a negligible effect on the distribution of the fuel andthere is no evidence of residual air flow. Therefore, to ob-tain as nearly a homogeneous mixture of fuel and air as possible,it is necessary to meter the fuel to the air in the combustionchamber by using the proper arrangement of the discharge orificeor orifices. The assumptions necessary for a practical basisfor these tests are that in carefully manufactured nozzles withround-holo orifices the coefficient of discharge will be thesame for all orifices, and that the same discharge pressure willbe acting on each orifice. These assumptions seem reasonable,and therefore all factors in the formula for quantities dis-charged becme identical, except for the areas, and it followsthat the amount of fuel discharged by each individual orificewill he proportional to the area of the orifice. If, then, eachorifice area is in the same ratio to the total discharge area asthe volume of air it serves is to the total volume of air served,the effectiveness of distribution will be dependent upon thedispersion of the fuel in the spray and the shape of the volumeserved.

To determine just how far it was advisable to follow thisprinciple comparative performance tests .were conducted with aseries of nozzles extending this idea beyond limits practicablein the construction of nozzles for commercial engines. ‘

To determine the optimum angle between sprays anotherseries of comparative performance tests was run with nozzles inwhich the orifice areas were held constant aad the angle varied.

Apparatus and Methods

The test equipment and general test methods used for thetests hereii~ reported are the same as in Reference 1, except asspecifically noted.

The co’mlmstion chamber was made as nearly quiescent aspossible by using a new throat orifice (Fig. 1) that had alarger opening than used in former te”sts and was so shaped asto disturb the orderly forced flow of the air as little aspossible and to”prevent residual flow and formation of smallvortices. The larger opening increased the clearance volume sothat the compression ratio was 12.6:1 instead of 13!6:1, as informer tests.

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IT,A.C.A. Technical Note No. 382 3< ..

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Compression pressures and maximum-cylinder pressures wereindicated by means of the balanced diaphragm type of maximum- ,.cylinder-pressure indicator (Reference 2) in place of thetrapped-pressure apparatus used in the former tests. Insteadof recording a double reading for maximum-cylinder pressuresas described in Reference 2, the operator recorded what heconsidered a fair average. No attempt was made to operate theengine at a particular “valu& of maximum-cylinder pressure;instead, the pump was adjusted to give the desired fuel quantityand then the timing was advanced until a faint knock was heara,i --

W1l-load fuel quantity 0.000325 pound per cycle is that”quantity of fuel which w-ill be completely burned, “assuming ~ei-fect comlnzstion, with the amount of air i“nducted per cycle at82,5 per cen”t volumetric efficiency. The test results are notcorrected $or either .%arometric presstire or humidity. The in-jection period as observed with an oscilloscope (Reference 3)was about 35 to 37 crank degrees. The standard test speed was1500 r.p.m,

S-cries E nozzles.- In the designing of nozzles for this ..——--———-—series of performance tests it was decided to abandon the

&8

angular syacing used in the former tests and to standardizepn an angl”e that would remain constant for all orifices. From

● data obtained from spray photographs by the Fuel Injection Sec-tion (Reference 4) on comparable orifices tested untier condi-tions comparable except for temperature, it was found that theaverage value for spray-cone angle was 20°. Twenty degreeswas t~erefore adopted as a staridard spray-cone angle for the

1 Serie~ E nozzles, and al~ air,-volune calculations were basedon this value.

To continue with a design of nozzle” that could be comparedwith those used in the former tests, the diameters of the 2central’ ma”in orifices were maintained at 0.018 inch and thevolume of air in the mechanical clearance space between theptston crown and the cylin’der head was divided equally betweenthese :orifices for purposes of proportioning the other orifices.A total of 16 orifices was used with 6 in one plane and 5 inea~h of 2 planes which were on either side of the first plane,as. shown in Figure 2. The orifices “were drilled 2 at a time inthe order itidicated by the numbering in Figure 2. The designa-tion of these nozzles is ,bj the use of the- letter E with anqmber derioting the number of orifices in the nozzle at ~h.etime of test.

There is a slight deviation from the proportional-areapriaciple i.~ the E-series nozzles after E12, because it wasconsidered impracticable to use orifices smaller than 0.005-”imch diameter. This aev$ation is not serious because the per-

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. . . .

N.A. C,A. Technical Not& No. 382

centage of the total orifice area involved is smaller than theexperimental error.

T%e performance test results sho~n in Figures 3 and 4indicate that no justifiable gain would be obtained by usingmore than 6 orifices for this cylinder head. This conclusionsimplifies further work with this cylinder head.

Series F nozzlos.- Thore were a number of indications——.——-—-—during these tests that the 20° angle between sprays was notthe optimum, and the decision to continue with the 6-orificenozzles made it comparatively easy to invosti.gate the effectOD engine performance of varying the augle between the axesof the individual sprays.

About this time the results of the work on dispersion atthe Pennsylvania .State College were published (Reference ~),and following the method outlined by Doctor Schweitzer theboundaries of combustion wore laid out for the EG nozzle asshown in Yigure 5. If the volume within this ~oundary is as-

. sumed to be a minimum space requirement. for combustion, it maybe SOEIII that the boundaries overlap and that the spr~~s prob-ably interfere with each other during combustion.

When the series 0$ nczzles for the investigation of theeffect of angular spacing was designed, it was again necessaryto deviate from the proportional-area principlo for the volumeof air to be served by each orifice chanced with the angle.However, as the orifice sizes were maintained the same for allangles, the departure from the proportional-area principleaveraged about 1 per cent, and this was neglected as it wasless than the error in the determination of performance values,Accordingly, the different nozzles were made with correspondingorifices of the same size.

The nozzles in this series are designated by the letter Fwith a number denoting the angle in degrees between the axes ofthe orifices. Thus , ~he EG ‘and the -1’~o arc identical nozzles.

The performance tests of these nozzles showed very littledifference between t“hem, so far as the curves in l?igure 6 areconcerned, but observation of the, exhaust gases and the sensi-

i

tiveness to controls led to the decision to standardize on anangle of 25° for future work with this cylinder head.

As a further check, to indicate whether the 29° spacirig was ,beyond the useful -limit, two 0.005-inch orifices were added,tothe l?~~ nozzle in the center to see if any unused air remained

—

between the 2 main sprays. The resulting increase in perform-●

N,A.C,A. Technical Note No. 382 5

ante, as shown in the curves of Figure 7, indicates that smallfiller sprays are effective when the angle between the sprayson either side is too great.

It is believed that a nozzle which would ‘be designatedF25 would give sufficiently good performance and that any in-crease which could be secured by further refinements in nozzledesign would hardly be commensurate with the complication in-volved in the construction of such a nozzle. However, the per-formance data do not show that angular spacing is at allcritical within the range covered in these tests. The reasonfor this lack of criticalness is suggested by the small per-centages of fuel in the outer part of the spray as shown %ythe dispersion data in Reference 5.

These tests do not complete the work to be done in in-vestigating the quiescent combustion chamber. In all teststhus far the total discharge area has been disregarded and con-sidered as a function of the injection system rather than of

. the combustion chamber. As it seems logical to investigatevariation in total discharge area along with variation in total “air available, additional data concerning this variation will

● be obtained in forthcoming supercharging tests.

..;

“ Conclusions.’

.

Although the tests ‘reported herein and in Reference 1were conducted on a particular cylinder head, they indicatethat there are de,finit.e basic. requirements which must besatisfied in the design of multiple-orifice fuel-injectionvalve nozzles for “u’se.in combustion with a quiescent combus-tion chamber to insure the necessary mixture of fuel and air.

The fuel-injection system should be so designed that thesame pressure is effective in causing the discharge througheach orifice. The orifices themselves should be of the samegeometric shape so that they all have the same coefficient ofdischarge. If these two conditions are satisfied, the nozzlewill be a%le to meter the fuel to the combustion air by havingthe area of the individual orifices proportional to the volume

. of air served by each orifice.

These engine performance tests show that, in a multiple-orifice fuel-injection valve nozzle for a quiescent combustion

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6 N.A.C.A. Technical Mote Ho. 382

chamber, there is no sharply defined optimun value for thenumber or direction of the orifices.

Langley Memorial Aeronautical Laboratory,National Advisory Committee for ACTOnaUti,CS,

Langley i?iold, Vs., Lfay x5, 1.931.

Reforoncos

1. Spanogle, J;”A,and

??oster, E. H.

2. Sparioglo, J. A.and

Collins, J. H.

3. Hicks, Chester ‘W.and

liooro, Charles”S.

4. Gelalles, A. (1.

.

5, Schweitzer, P. H.

a Porformancc of a High-Speed.Compr6ssi,on-Ignition Engin6”Using Multiple-Orifice TuelInjection Nozzles. N,A,C.A.Technical Note No, 344, June,1930.

.

: A Balanced Diaphragm Typo of.

Maximum Cylinder PressureIndicator. I?.A.C.A. TechnicallTote Ho, 359, Dec., 1930.

4

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: The Determination of SovcralSpray Characteristics of aHigh-Speed oil Engino Injec-tion Syst~m with an Oscillo-scope. N,A,C.A. TechnicalNote No. 298, Sept. , 1928.

: Effect of Orifico Longth-Dianf3tcr Ratio on SprayCharacteristics. IT,A.C,A.Technical lroto No. 352, Oct.,1930.

: Factors in Hozzle Design inthe Light of Recent Oil SprayRosoarch. No. OGP-52-15.page 121, Yransactionn ofA.S.M.E. , 1930.

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