CONVOCATORIA DE AMNISTÍAS TRIBUTARIAS

The conventional w ay of supplying fuel under pressure to the injectors is by using an electric fuel p u m p and pressure regulator (figure 4.9). W ith this type of system excess fuel is continuously spilled back to the fuel tank and consequently the m inim um quantity of fuel in the system is of the order of several litres. W hen the choice of hydrocarbons to be used as test fuels w as u n der consideration it became clear that their cost w as going to be very high in some cases. This provided motivation to arrange an alternative fuel system w hich could reduce the quantity of fuel involved in a given test, and m ake change over betw een fuel blends relatively stra ig h tfo rw a rd .

The solution was the conception, design and adoption of an air-pressurized fuel system. This system used com pressed air to displace the fuel from a sealed cylinder into the fuel rail. A part from providing compression of the fuel, the air played no other role in the atom ization process. H enceforth this supply method will be referred to in this w ork as the 'air-fed' fuel system . This sh o u ld not be confused w ith a ir-assiste d injection w h e re th e fuel is conventionally pressurized and air is provided at the injector tip to im prove atom ization. A general arrangem ent of the system is given in figure 4.11.

The design of the containm ent vessels utilised a sim ple arrangem ent of m achined alum inium tube w ith base and top flanges, held together w ith four studs. The tube w as sized to allow insertion of a 250 ml pyrex cylinder in which the fuel w as contained. The top flange had a union for connection to the compressed air supply, and one for connection to the fuel line. The fuel line union included a dip tube', such th at w h en the top flange w as fitted and the air supply turned on the fuel was taken from the bottom of the pyrex cylinder and forced u p the tube. The advantage of this system was that there w as no pressure loading on the pyrex cylinder itself; this w as taken by the alum inium vessel, w hilst the fuel w as easily changed by sim ply changing the pyrex cylinder. A photograph of the pyrex cylinder and containm ent

vessel is given in figure 4.10, with figure 4.12 show ing an early draw ing of the containm ent vessel construction. Design drawings are given in appendix C.3.

The air-fed system w as used extensively for the M alvern tests, alth o u g h it w as still necessary to use the conventional pum p system during the m easurem ent of fuel flow rates.

4.4 PHOTOGRAHIC SYSTEM

The operation and arrangem ent of the M alvern particle sizer w as discussed a t some length in previous chapters. However, so far little has been said about the p h o t^ a p h ic system. The system used w as one w hich was m arketed by a com pany called Pulse Photonics. The arrangem ent can be seen in figure 4.13 and was as follows:

Illum ination w as provided by a 6 Joule argon-shielded spark-flash unit. This gave an exposure tim e of around 500 ns and was used to back-light the spray via a diffuse screen. Still images w ere captured on video using a m onochrom e CCD camera w ith telescope lens. Events w ere synchronised using a frame store a n d tim ed trigger unit. The video 'stills' w ere converted to hardcopy as required. W hilst sim ultaneous photographic and LD m easurem ents w ere not possible, m easurem ents were m ade at the sam e position in the spray, both in space and time.

4.5 INJECTOR AND MEASURING SYSTEM TRIGGER ARRANGEMENTS

Injector drive circuitry was provided by a Bosch m anual control unit, w ith control stage Y280 V400 01050 and drive stage Y280 V400 01055. This provided variable pulsew idth control via a g rad u a ted potentiom eter dial. A trigger signal for this u n it was provided by the M alvern spray synchroniser, via the low tension term inals of an ignition coil. The latter ensured a trigger pulse of the form required by the Bosch unit.

There w ere two m ethods adopted for providing tim ed injection events, one for using the M alvern particle sizer, and the other for using spark-flash photography. For M alvern drop- sizing the spray synchroniser produced the initial tim ed trigger, either using its internal tim er, w hich produced repetitive triggering at a user defined repeat rate (frequency), or using its single-shot button w hich provided a single trigger only. This un it also provided a user defined delay betw een injection trigger and M alvern m easurem ent trigger, in order to allow for the electrical and fuel transport delays betw een injection trigger and the spray reaching the m easurem ent zone.

For spark-flash photography the initial trigger w as produced by the Pulse Photonics tim ed trigger unit. This w as a single shot device w hich provided an external trigger in p u t to the M alvern spray synchroniser, which in turn triggered the Bosch unit. The tim ed trigger unit

also provided trigger signals for the spark-flash and fram e-grabber, at a user defined delay after injector trigger (again allowing for electrical delay and fuel tran sp o rt time).

The arrangem ent of and connection betw een the various com ponents of the triggering and m easuring system is given in figure 4.13.

4.6 MALVERN LENS EXTENSION

W hen attem pting to solve the problem caused by evaporating fuel in the m easurem ent zone, discussed in chapter 3, it became necessary to extend the range of the M alvern particle sizer. This involved increasing the focal length of the u n it to 600 m m by fitting a n ew lens. U nfortunately this could not be fitted to the standard M alvern receiver un it w ith o u t some m odification. In ord er to fit the 600 m m lens it w as necessary to construct and fit a lens extension tube. The tube and clam ping arrangem ents w ere designed to fit the p u rpose built vertical bed on which the M alvern was m ounted. Design draw ings are given in appendix C.4.

4.7 INJECTOR TEST BOOTH

For the fuel flow m easurem ents the steady air flow rig w as not used, b u t instead the decision w as taken to spray the fuel into the am bient atm osphere (free-air) a t the req u ired fuel pressure.

O bviously this required some form of containm ent and extraction. The m ethod th at was adopted w as to m ount the injector on a retort stand above a funnel. The funnel w as connected by pipe to the vacuum pum p via the d a m p in g /d ilu tio n cham ber. A test booth w as then constructed w hich could be p u t over the injector/funnel arrangem ent. The booth w as fitted w ith electrical connections and fuel line unions to allow the injector d rive circuit and fuel supply to pass through its walls. A door was fitted to enable access to the injector, and a vent w as fitted to enable atm ospheric air to be draw n into the booth.

The vacuum pum p was used to draw the air and fuel from the booth, w hilst the vent in the booth w all allow ed fresh air to enter, ensuring the fuel v a p o u r d id n o t escape. A useful feature of the booth was that it w as fitted w ithout a floor so th at it could be m ounted over any arrangem ent of injector which was set u p on the m ain bench of the test facility. Thus the bench provided the floor of the booth.

4.8 REFERENCES

[1] M iller, M.J. M ixture Preparation in A utom otive Spark-Ignition Engines - with

particular reference to m ultipoint fu e l system s. PhD thesis. D e p a rtm e n t of

Mechanical Engineering, University College London, 1992.

[2] M iller, M.J., N ightingale, C.J.E. M easurem ent of the changes in m ixture preparation that occur during flow past the inlet valve of an si engine. Paper C394/004,1.M ech.E. In te rn atio n a l C onference on A u to m o tiv e P o w er System s, C h ester, UK, 10-12 September, 1990.

[3] M iller, M.J., N ig h tin g ale, C.J.E., W illiam s, P.A. M easurem ent of sp ark ignition engine m ixture preparation and assessm ent of its effects on engine perform ance. Paper C433/022,1.Mech.E. International Conference on Internal Com bustion Engine Research in Universities, Polytechnics and Colleges, I.Mech.E, HQ, London, UK, 30-31 January 1991.

[4] R okita, R., Bandel, W., Herzog, P. M ixture p rep a ra tio n optim ization for gasoline engines on a dynam ic flow test rig. Paper C 465/032/93, I.Mech.E. International C onference on E xperim ental and P redictive M ethods in Engine R esearch and Development, NEC Birmingham, UK, 17-18 N ovem ber, 1993.

4.1 Cross-section through a Zeta 2B inlet tract

g

cokse

NATL:

DIMENSIONS In mm UNLESS STATED QTY: SCALE:

Ford Zeto 20 Series Intake