Fuel Meter Model FM 200

Transcription

1 Fuel Meter Mdel FM 200 WILLIAM C. KIELING, Assistant Prfessr f Mechanical Engineering, Cllege f Engineering, University f Washingtn The mtr benefits fuel meter is an Accurate, _. wide flw range fuel-measuring device designed, fr use in fuel cnsumptin tests f large gasline- and diesel-pwered highway vehicles. The meter is virtually uneffected by nrmal changes in flw rates, fuel pump pressures, electrical vltage, ambient temperatures, and vehicle ride. VEHICLE STUDIES at the University f Washingtn invlving measurement f fuel have resrted t use f calibrated burettes placed in the cab f the test tractr. This arrai^ement, althugh satisfactry, has the undesirable features f large space requirements, excessive installatin time, and the fire hazard f liquid fuel in the cab. This fuel meter is the utcme f numerus discussins fr a mre simplified methd f measuring the fuel cnsumed by the test vehicles. Cmmercial fuel measuring devices are nt available that have the features f cvering the flw rates encuntered and the accuracy desired, and that can be easily installed and carried in a test truck. THE METER Figure 1. Fuel meter mdel FM 200 with cunter mdel FM 201. The meter (Fig. 1) is a vlumetric fuel-measuring device cnsisting f a slenidactuated, air-perated valve and tw measuring chambers. In peratin, fuel enters a flat-cntrlled vapr separatr where liquid fuel is separated frm vapr r air. The liquid fuel passes thrugh the valve int ne end f a duble cylinder fitted with a hi

2 48 free-ftating pistn. On entering the chamber at ne end f the cylinder, the incming fuel mves the pistn which in turn discharges fuel frm the secnd cylinder int a surge chamber and ut int the fuel line. At the end f the pistn travel, an electrical switch is actuated by the pistn, causing the slenid valve t interchange inlet and utlet prts f the tw chambers. The measuring chambers are alternately filled and exhausted by actuatin f the valve. A magnetic digital cunter in series with the slenids f the valve will recrd each actuatin f the valve. By having a predetermined pistn travel, the cylinder vlume can be established; and hence, the quantity f fuel passing thrugh the meter is knwn frm cylinder vlume and number f times the cylinder is filled. Pistn travel is limited t give a cylinder vlume f apprximately ml which gives apprximately 1,380 cunts per gal. This can be altered t give a greater r lesser number f cunts per galln by changing spacing f the electrical switches. With an increased number f cunts per galln, the peratinal perid f the meter between servicing will becme prprtinally reduced. Because the electrical switches and O-rings are subject t much use, their life will determine the length f peratin between nrmal replacement f these items. The perid between meter servicing shuld be the time required t meter apprximately 500 t 700 gal f fuel. A fuel pressure drp thrugh meter ranges frm 1 t I'A psi at flw rates crrespnding t nrmal truck fuel use. A bster fuel pump is recmmended in additin t the vehicle fuel pump t insure prper engine peratin. Installatin f Meter Reference t Figures 2 and 3 is made when making the meter installatin. Digital Cunter air supply Carburetr. - Bypass valve (pt) 12 vlt d c- fuse Fuel tank Fr diesel applicatins substitute detail n fr I frm meter mjectr return Fuel pump Figure 2. pump return - Day tank Installatin diagram. 0 pump

3 49 RHSOL L.H SOL < 7 ' RHSW COUNTER ASSY FM 201 (REF) OVERRIDE SW. (REF) 6 GND CNTR - BAT FUEL METER ASSY FM 200 Figure 3. Wiring diagram. The meter is installed in an upright psitin in the engine cmpartment f the vehicle being tested. The extreme temperature area f the ediaust manifld shuld be avided. Munting f the meter in ther than an upright psitin will hinder peratin f the flatcntrlled vapr separatr and may permit fuel t pass directly frm the vapr separatr t the surge chamber withut being measured. Inasmuch as installatins will vary s widely, n specific munting directins are given but left t the discretin f the instrumentatin mechanic. Tw hles have been prvided in the bttm f the cver plate fr anchring the meter t a hrizntal shelf; and.tw hles, tapped 1/4-20 UNC, have been prvided in the rear side f the base plate fr attaching the meter t a vertical bracket r bulkhead. The meter may als be suspended by clamps placed arund the slenid cvers. Suspensin by attaching t the Vt-in. cpper air line is nt recmmended. Fuel lines are cnnected as indicated n the installatin drawing. Cpper fuel lines may be used in place f flexible lines if n relative mvement exists between fuel pump, meter, and carburetr. Check t make sure the fuel flw is in the prper directin thrugh the meter. A bypass valve is recmmended t permit fuel t be diverted past the meter if meter failure ccurs. An air siqiply is cnnected t the Vt-in. tube tee n ne slenid. A flexible line shuld be used unless relative mvement is small. On vehicles that nrmally have an air cmpressr (heavy trucks), the air cnnectin is made directlyt a cnstant pressure

4 50 line frm the air tank and reduced t the required pressure. If the vehicle is nt equipped with a cmpressr, a nitrgen r air cylinder (2, 000 t 3,000 psi) can be carried in the vehicle with necessary pressure regulating equipment. Air supply pressure is adjusted t 20 t 25 psi. When new O-rings are installed, the 20 t 25 psi may nt be enugh fr peratin f the valve and a slightly higher pressure may be required. "Pund ut" f the valve may ccur if excessive pressure is used. Electrical cnnectins are made using 18-gage wire r heavier. A small autmtive fuse (9 r 14 SEE) shuld be used t safeguard equipment in case f an electrical shrt circuit. Fr cnvenience the meter and any electrical fuel pumps shuld be cnnected t the ignitin switch. The electrical crd supplied with the magnetic cunter (FM 201) has slderless terminals at ne end fr cnnecting t the meter. Althugh the wires are f different clr, interchanging the leads makes n difference in meter peratin. K the meter is used with a negative grund, the dides shuld be reversed. The meter requires apprximately 1 amp at 12 vlts. Calibratin Labratry calibratin (Figs. 4 and 5) f the flw meter was accmplished by recirculating fuel frm a supply tank and thrugh a series arrangement f an electric fuel pump, the meter, a needle valve, a three-way valve, and back t the supply tank. The needle valve was used in regulating the flw t permit calibratin fr any flw rate that may be encuntered in the field. Fuel was recirculated until a calibratin was t be made, at which time the three-way valve was used t divert fuel int a graduated burette while a predetermined number f cunts were registered n the digital recrder. Fuel quantity, digital cunter recrd, and time t meter the given quantity were all recrded fr use in preparing a calibratin chart. Fuel quantity was usually the quan- Figure li. Labratry c a l i b r a t i n arrangement.

5 ^ I300F U 1_ Q- / ml /C 1380 C> 'gal O ISOOh Cunts Per Minute Figure 5. Calibratin chart Pistn Measuring Chambers Air HI Valve Assembly Air Sl Air Supply. T FueL0ut_4Surge Chmber Vapr Separtr JFjiel In Figure 6. Schematic arrangement.

6 52 tity crrespnding t 100 cunts n the recrder. Fuel inlet and utlet pressures were als recrded every time a significant change was made in the flw rate. Field calibratin was als perfrmed by installing the meter in series with the burette fuel measuring equipment in the test truck. Labratry and field calibratin were In very gd agreement. Trubleshting Erratic peratin f the meter is prbably due t air in the fuel line r a large rati f vapr t fuel. The vapr separatr will functin prperly with lw vlume f vapr in the fuel lines, but the meter will becme erratic when air r vapr is admitted t the measuring chamber. Erratic peratin shuld cease after a few minutes peratin unless there is an air leak r restrictin in the suctin line. A restrictin in the suctin line will cause a prtin f the fuel t vaprize because f the reduced pressure. If meter fails t start, valve spl may nt be psitined prperly. With a screwdriver, ne f the pistn limit switches is actuated (r ne f the tw verride switches depressed). If the meter has nt started, air pressure, fuel pressure, and electrical cnnectins shuld be checked. When actuating the electrical switches, there shuld be an audible exhaust frm the slenids. If air pressure is great enugh, the spl can be heard mving in the valve when the switches are alternately actuated. S the meter stps at lw flw rates, it is prbably because fuel is bypassing the O- rings. Tw f the six O-rings are replaced n the valve spl, the secnd ring frm each end f the spl. The ring and cylinder shuld fit snugly when the ring is prperly installed n the spl. These tw rings are critical items in the meter. Manufacturing tlerances fr the rings are t wide t permit the use f all cmmercial O-rings fr this applicatin. If the meter stps at any flw rate but can be started by actuatin f verride switches, then prbably life expectancy f electrical switches has been shrtened by permitting switch t becme saked in fuel. Bth switches shuld be replaced. If there is visible fuel slenid exhaust, then end O-rings n valve spl shuld be replaced. If the verride switch des nt actuate slenid valve, then prbably there is pr electrical cnnectin, r electrical limit switch is in clsed psitin due either t pistn actuatin r t defective switch. ' If the meter is "dead", but all external electrical cnnectins are gd, pr electrical cnnectin between meter and cunter shuld be checked. This is a series electrical circuit and gd electrical cntinuity must be maintained. If meter calibratin is nnlinear, fit f number 2 and 5 O-rings shuld be checked, and O-rings nt having a sung fit in cylinder replaced. U the meter des nt recalibrate after changing electrical switches, then switches may nt be tight against micarta blck f switch assembly. Applicatins The fuel meter is intended t be used in vehicle testing and can adequately measure fuel at flw rates crrespnding t all highway vehicles using gasline r diesel fuels. The meter is nt suitable fr cnstant use n highway vehicles, because its initial cst and peridic servicing wuld make it impractical. When using the meter t measure fuel cnsumptin f diesel vehicles having a recirculating fuel system, a flat-cntrlled "day tank" must als be used. Using the day tank, an equivalent vlume f fuel is measured instead f the actual quantity entering the vehicles injectrs. Imprvements A direct acting slenid valve replacement fr the air-perated slenid valve wuld permit a better applicatin n test vehicles nt equipped with a cnstant pressure air supply such as fund n large trucks. Slenid life and high current fr the small electrical switches will be prblems faced when redesigning fr the direct acting slenid valve.

7 Future fuel meters using the air-perated slenid valves shuld be redesigned sughtly t incrprate a valve built t tighter valve spl tlerances than the cmmerciauy available valves. This shuld nt change the meter except in appearance. The meter shuld be scaled dwn in future changes t prvide fr better peratin at the extremely lw flw rates. Presently the meter perates best at rates abve idle fuel flw rates. CONCLUSIONS The Mtr Benefits fuel meter will measure mtr vehicle fuel cnsumptin frm idle t wide-pen thrttle peratins with accuracies better than any cmmerciauy available meter. Althugh research persnnel at the University f Washingtn have nt used this meter exclusively fr vehicle fuel cnsumptin tests, they have had gd crrelatin between labratry tests and field tests and have used the meter t measure in excess f 700 gal f fuel between service perids withut majr difficulty r any meter cmpnent replacements. ACKNOWLEDGMENT This meter was develped as part f Research Cntract CPR with the Bureau f PubUc Rads. 53