GRV-2 Jet Bike Project 1/17/10

Posted on January 17, 2010

       Hello again everyone!!! The GRV-2 project has come a long way in the last few months. Countless hours of preparation have lead me up to this point and I couldn’t be any happier with the results. However I still have a few details to sort out before the big speed run day. I still need to test out the ACM and fine tune the AB fuel pressure settings as well as the activation points.

       In the last article I had just installed the ACM (Afterburner Control Module) into the bike and was preparing for a test firing at my local “test facility”. During the time I was waiting for a good day to test I decided to add a few items to the bike (out of boredom mostly). One of these items was to add a dust cover for the underside of the control panel. The cover will help keep dirt out of the gauges and switches during future lake bed runs.
       I fabricated the cover out of aluminum sheeting and fastened it to the frame of the bike as seen below. The red button at the front of the cover is the fuel tank breather filter.

       Another little detail that I wanted to add was a set of “tail lights”. I had seen these 12 volt LED side marker lights at my local Lowe’s and just had to buy a set for the bike ;0)

       I drilled out the rear frame to accommodate the LED side markers and installed them with 8-32 stainless hardware.

       And voila!!! I now have a full LED lighting system :0)

       After some minor planning I was prepared enough to trailer the bike out to the testing grounds for an afterburner test. My plan was to check the ACM for proper operation as well as set up the activation points for the two stage fuel delivery system.

       I packed up the GRV-2 and trailered it out to the test site for another go around. Once there I set up shop with the assistance of my good friend Adam Hicks who had helped me with the first test of the afterburner. We fueled up the bike and warmed up the GR-7 to full operating temperature before arming the ACM for an automatic burn cycle.
       I used the manual mode button to test the fuel flow through the injector nozzles. Once the fuel system was purged of air I switched to automatic mode for an ACM test. The bike was throttled up several times to set the low speed activation point for the fuel system. After several attempts the low speed combustor pressure switch was dialed in to about 10 PSI (43,000 engine RPM). This is the speed at which the burner will ignite reliably without issue.

       Once the burner was warmed up I was able to set the high speed combustor pressure switch to activate at 20 PSI (61K RPM). This is the speed at which the burner will go into full power mode and deliver about 26 GPH of diesel to the fuel injectors. The afterburner was really rocking now!!!

       I spent some time studying engine temps and pressures to fine tune how much fuel would be needed for an optimal burn rate. Too much fuel started to cause excessive back pressure for the engine and raised the turbine temperature to above normal limits. After several tanks of fuel I was able to set the fuel flow to about 24 gallons per hour (50 PSI) which was in perfect harmony with the GR-7’s temps and pressures.
       The GR-7 was also tuned to max out at 66,000 RPM without the burner running as to not allow the engine to overspeed should the burner flame out during a run. This was done by setting the GR-7’s existing “top end” fuel flow valve to limit the overall fuel flow from the fuel pump. I ran the engine to full power several times without the burner being activated to assure the engine would not overspeed (due to the loss in back pressure that would normally be created by combustion in the burner duct).

       The ACM was working flawlessly at this point allowing me to stress test the engine for extended periods of time. I wanted to make sure that the burner duct could handle the 2400° F exhaust gasses without warping or worse yet, melting!!! The burner was run at full power for a two minute period during which the burner duct was completely glowing yellow. Fortunately the 304 stainless pipe I used for the burner held up really well considering how brightly the metal glowed.
       Oddly enough, the video camera used to tape the test was especially sensitive to the infrared light produced by the glowing metal. We had noticed that the camera really accentuated the light produced by the infrared radiation at night. The glow of the metal as well as the bluish flame in the jet exhaust was far less noticeable during the day.

See the ACM test video here!!!

       The infrared radiation form the burner duct was quite noticeable. The heat could be felt from several feet away. Luckily the heat shield I had installed earlier over the tire was working like a champ. The fender and tire remained cool to the touch which is better than I could of asked for.

       The sound of the burner was thunderous!!! I was really impressed at how much energy was being converted in such a small space :oP

       Once I was satisfied with the operation of the burner I packed up the bike and headed home. I carefully inspected the burner duct for erosion or warping due to the intense heat it was subjected to. Luckily there was no damage to the metal whatsoever, only discoloration caused by oxidization. 

       The heat shield worked incredibly well at protecting the rear tire and fender. Only a slight discoloration of the shield was noticeable.

       The infrared heat was evident by the charred paint on the duct support frame seen below.

       The stock automotive plug wire did not fare so well on the super hot spark plug. The wire boot was effectively turned to mush as the plug was probably heated up to 1800° F or so!!! A proper boot was needed as a replacement.

       I fabricated a new plug wire boot out of some high temp rigid silicone tubing. This time the boot only covers the very end of the plug which should help the boot survive a bit longer than the old one did :oP

       After further inspection I had noticed that the burner duct was expanding quite a bit more than I had anticipated. In fact the duct was expanding as much as 10 mm end to end!!! Even though the duct cradle was designed to allow the duct to slide back and forth it was proving too much for the constant tension hose clamp used with the cradle. The clamp was becoming warped and stretched out, more than I wanted to see. This would need to be fixed before the next speed run.
       I decided to add a set of “linear slides” to the duct cradle to allow it to expand freely without binding on the hose clamp. I used a set of 5/16”-24 shouldered bolts and welded in slide bushings to create the slide as seen below. It was a relatively easy fix and worked like a charm!!!

       I replaced the old 6” constant tension hose clamp with a new one and then tested the slide with the engine running. The cradle moved back about 4 mm when the engine was at running temperature justifying my decision to modify the cradle (not shown).

       Now that I was satisfied with the overall operation of the burner I felt confident enough to test the bike again for an official static thrust rating (what we have all been waiting for). I had yet to do this mostly because I was more concerned with the engine running properly. Now that my concerns were at rest it was time to break out the scale and fire up the bike!!!
       Once again the bike was brought out to the testing grounds and set up on a level concrete pad. I hooked up my dynamometer scale to the bike via a set of tie downs and fired up the bike with great anticipation. After several warm up burns I removed the parking brake and kick stand for a full scale pull test. I carefully balanced the bike with the handlebar and throttled up the GR-7 to full power.
       I was unable to see the swing of the scale needle so I had my buddy Adam film the scale as I went through the throttle range. After the engine was shut down we reviewed the tape and I was happy to see the scale needle stabilize at 67 pounds at full power!!! That means that my original estimate of 30% increase was almost spot on.

See the thrust test video here!!!

       After running the engine a few more times I became aware that the afterburners duct temperature had a direct effect on the thrust produced. Seems that the hotter the duct became the more thrust the engine would produce. On initial fire up the burner would peak as high as 75 pounds and then stabilize at 60-68 pounds depending at how hot the burner duct was. it is possible that the hot duct is more conducive to the combustion process over a cooler duct.
       I am quite positive that I could achieve 75+ pounds of thrust if I were to push the GR-7 to it’s limits. However I want the engine to last me a while and also reduce the risk of a failure when I am riding it at high speed. Fuel consumption is also something to consider as the bike will now drink up 3 gallons of fuel in just 4.5 minutes of running at full power!!!

       Now that the numbers are in I can finally say that all of my goals for the GR-7 have been met in full. Not only did the GR-7 meet my goals it exceeded them. The GRV-2 as well as the GR-1, GRV-5A, GR-7 and the GRV-1 has proven to be quite an educational tool that I probably could not have received at any school. I value this experience as one of my most memorable technical projects to date and I am super happy I was able to share it with my readers.
       I can’t get all sentimental just yet! I still have the speed runs to conduct. I am fairly sure I will beat my 52.1 MPH mark but by how much? We will have to wait and see.....................

       For now the GRV-2 Turbochopper is ready for the next speed run. I am now in the process of organizing the next trip to the dry lake bed which will hopefully happen within the next few months. Until then be safe with your projects and thanks for spending some time on my humble little site!!!

Don R. Giandomenico - DRG Engineering


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