Posted on December 16, 2009

       Hello again folks! This week I decided to work on the fuel pump manifold for the GR-7’s afterburner system. The new manifold will help regulate fuel flow to the mixing chamber nozzles as well as provide back flow protection and duel filtration for the fuel system. The manifold will consist of a pressure bypass valve, one way check valve, 10 micron sump filter, 90 micron nozzle filter and a fuel pressure gauge. On top of that somewhere I plan to fit a set of pneumatic pressure switches which will help control fuel flow later on.
       To control the overall fuel pressure from the fuel pump I will use a pressure bypass valve. The hydraulic needle valve seen below will bleed off excess fuel pressure generated by the fuel pump back to the fuel pump’s intake or sump. The bypassing of the fuel pressure from the injector nozzles will essentially allow me to manually adjust fuel pressure at the nozzles.

       My overall plan is to build a two stage fuel flow system for the burner. This system will be controlled by two pneumatic pressure switches that will tell the future Afterburner Control Module or ACM when and how to activate the fuel pump. The pressure switches will be plumbed into the engine’s combustor pressure line which will tell the controller how fast the engine is spooling. The first pressure switch will monitor the low speed burner activation point and the second one will monitor the high speed full-afterburn activation point.
       The high speed full-afterburn setting will require about 50 PSI of fuel at 26 gallons per hour. This fuel flow rate will be adjusted with the pressure bypass needle valve (with the fuel pump running at full speed). At low speed burn I will reduce the actual speed of the pump motor to slow down the fuel flow to about half that of the full burn rate. This will be done with a set of power resistors in series with the pump motor (later on).
       The hydraulic needle valve I am using here is the same type unit I used in the GR-7’s fuel delivery system back in ‘06. The valve is used on the engine as a high speed fuel flow restrictor which will ironically be used later on to fine tune the GR-7 to the afterburner. In this case the new bypass needle valve will be set to relieve afterburner fuel pressure to about 50 PSI and then locked into position (You will notice that I removed the “T” handle from the valve so that a flat bladed screwdriver can be used to adjust the valve when it is installed into the bike frame).

       I gathered up the pile of brass fittings which will make up the body of the manifold. It is now just a matter of threading them together correctly :0)

       I started out by building the pressure bypass circuit first. Permatex thread sealant was used on all of the threaded joints to insure no leaks in the future.

       The next step was to install the check valve and 90 micron injector filter in line with the “high side” of the pressure manifold. The check valve (seen below/top) will be used to insure that fuel from the injector manifold will not be pushed back into the fuel tank when the pump is not running. The pressure differential between the outside air and the mixing chamber at full power could be as high as 10 PSI which is plenty of pressure to send fuel or exhaust gas rushing back to the tank.
       The 90 micron inline filter (seen below/bottom) will keep any metal flakes generated by the mechanics (pump and valves) from entering and clogging the fuel injectors. The 90 micron particle rejection rating will adequately protect the nozzles and still allow proper fuel flow without restriction.

       The next system to assemble is the pressure switch manifold. This manifold will hold two Nason SQ-2 adjustable pressure switches (McMaster-Carr Cat #3460K41). These compact switches (below) will eventually be responsible for activating the two fuel pump rates.

       The black thumbwheel adjuster on these switches will make for easy adjustment in the field without any tools.

       I now needed a good mounting location for the manifolds and fuel pump. Luckily I had already planned for this by leaving a little room just in front of the fuel cell ;0) I prepared a mounting bracket for the manifold “tree” and pre drilled it for hardware as seen below.

       The next step was to build the manifold tree. I used some 1/2” square tubing to build the trunk and miscellaneous pieces to build the branches.

       I used a set of hose clamps to secure the pressure manifold to the tree. Simple yet effective.....

       The pressure switch manifold was attached to the tree in the same manner. You can see that I tried to compact the assembly as much as possible to save space :0P

       The next item I installed was the Summit Racing fuel pump.

       A paper element fuel filter was added to the tree. This filter will scrub the fuel that enters the system from the tank sump.

       And now for the rubber fuel hose. I used some 5/16” Goodyear rubber fuel hose to connect the manifold to the filter and pump. The hose is good for up to 50 PSI which should be perfect for my application.

       Once completed I bench tested the manifold/pump with diesel fuel to see how well the bypass needle valve worked. I used a smaller needle valve to act as a substitute for the flow restriction that would normally be created by the injectors (not shown). The pump worked exceedingly well to keep up with the 26 GPH demand at 50 PSI (pump draw was 6.5 amps @ 12.5 volts). The bypass valve worked very well in controlling the overall pressure allowing for very precise adjustment :0)
       I varied the voltage delivered to the pump to see if I could controllably reduce the fuel pressure with pump speed. I found that by reducing the pump voltage to 8 volts (4 amp draw) will cause the fuel pressure to drop to about 25 PSI @ 18 GPH. This flow rate will work perfectly for for my proposed “low speed” burn rate. I will just have to add a resistor bank to the pump driver circuit to control this lower pressure mode.

       I moved the whole assembly over to the bike to attach it to the frame. Two 1/4”-20 stainless bolts were used to hold the manifold tree to the frame as seen below. Just enough room!!!

       I used the spare 1/8” NPT fuel sump port on the fuel cell to tap the new pump manifold into the system. Hopefully the fuel cell sump tube will be able to deliver the 1.3 fl ounce per second fuel demand from the engine in full afterburner mode :oP

       I now needed to plumb the injector manifold to the new pump manifold. I used some 1/4” OD soft-drawn copper tubing to make a rear fuel line for the burner assembly. Using a flare tool and a tubing bender I created a custom line for the injector manifold.

       I transitioned the copper line to a high pressure nylon tubing at about the middle of the engine (see below). The nylon tubing will make for a better disconnect point than rigid tubing and is much easier to weave through the existing engine parts. I would of used nylon tubing for the whole length of line but I had to consider the radiant heat produced by the rear of the engine. Last thing I would need would be raw fuel spraying on a red hot engine!!!

       I attached the nylon tubing to the fuel pump manifold which completed the fuel delivery system.

       One last thing I needed to do was tap into the combustor pressure line for the pressure manifold. I used some 1/8” high pressure nylon tubing to tap out of the existing combustor pressure line that feeds the “boost” gauge in the instrument cluster.

       A “tee” compression fitting was used to tap into the existing pressure line as seen below.

       I can now concentrate on how I am going to build the afterburner control module. Hopefully I will have time this week to get some ideas on paper for the control logic of the ACM. Once on paper I should be able to build it fairly quickly which is good considering I really want to ride the bike again. I can’t wait to see how fast this thing will go now that it has some real firepower!!!! :0)))

       Please join me for the next chapter in the GRV-2 Turbochopper build!!!

Don R. Giandomenico

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