GR-7 Turbojet Engine Project 8/14/09

Posted on August 14, 2009

       Hello folks!!! I have finally got back my turbo parts from the balancer and I am anxious to get the GR-7 back into running condition. I had recently modified the main evaporator nozzle and it was time to install it into the combustor end plate. The nozzle position was moved toward the bottom end of the evap tube assembly to increase evaporation efficiency. Hopefully the shorter tubes and improved nozzle location will keep the new tube assembly cooler.

       The next step was to install the evap tubes onto the new injector nozzle as seen below.

       When I originally built the evaporator assembly I had incorporated hardware with safety wire holes. It was now time to use the holes to secure the cap screws with safety wire. I used a .032” stainless steel safety wire to tie the cap screws into place as seen below.

       The flame tube was the next part to install onto the assembly. Once again I used safety wire to secure the 1/4-20 cap screws into place.

       It is very important to use an anti-sieze agent on all stainless screws and bolts, especially 18-8 stainless. This will help prevent the threads from sticking to each other and ruining your day. This comes from experience :0/

       The combustor end plate was bolted onto the combustor and re-plumbed into the fuel solenoid manifold.

       I unpacked the turbine wheel assembly as it was sent to me from the balancing facility in preparation for reassembly. I had noticed the orientation marks left by the balancing tech on the backs of the turbine and compressor wheels. These marks will need to be aligned to each other in order to preserve the dynamic balance of the wheels.

       A very small amount of metal was removed from the wheels to improve balance. This is a good sign as the wheels were already very close to perfect when they were run in the engine before. Having them tuned up is just good insurance.

       The oil seals were reinstalled onto the shaft and thrust washer. This is done very carefully as to not scratch the thrust surfaces with the sharp ring edges. A coat of motor oil was applied to the shaft before installing it back into the center housing. The oil seals were placed at 10:00 and 2:00 o’clock on the hot end and 12:00 o’clock on the thrust washer in relation to the oil drain hole. This will help keep oil from leaking out of the housing later on.

       I reinstalled the compressor nut onto the turbine shaft and tightened the assembly to 30 ft/lbs. I used “blue” locktite on the threads for insurance. I double checked that the turbine and compressor wheels had kept their orientation to each other insuring proper balance. You will notice that the compressor nut looks a little different than before. This is because I had chosen to sand blast and repaint the nut to work more efficiently with the tach photo sensor. The “gun blue” treatment I had applied to the nut earlier did not work as well as planned. A flat black and white lacquer paint was used to paint the nut with clear topcoat of polyurethane to ward off any rust.  

       The turbine “stack” was assembled and refitted with the starter assembly. I carefully realigned the starter shaft to the compressor nut to eliminate binding. This is an important step and must be done right to prevent a starter malfunction later on.

       The VT-50 was reattached to the combustor and rewired to the ECU box. The oil pump was run and oil flow was checked at the turbo drain for proper volume.

       I used the starter system to spool up the turbine to check for any binding before attempting a start. Everything checked out fine so I attached the jet nozzle pipe to the turbo in preparation for a test run.

       I charged the battery for a few minutes and then switched on the ECU for a test run. I was getting proper fuel and oil pressure as well as a green light on starter engagement so I flipped the start switch. Just like clockwork the engine spooled up to ignition speed and that slight grumble of burning fuel was present once more. After the minimum burn timer switched off the engine spooled up to full starting speed singing it’s beautiful turbine whine :o)
       The engine was running silky smooth thanks in part to the balance tune-up. I put the engine through it’s paces once again to see how the rebuilt evaporator tubes were doing. There was no noticeable change in performance from the old tubes to the new ones which is a good indicator that the new evap tubes were doing their job. The EGT levels remained the same throughout the power “band” suggesting that the new evap tubes were able to “process” the high flow of fuel passing through them.
       The modified Hago evap nozzle was working correctly as well allowing me to reduce the fuel pressure back to 95 PSI. At full throttle I was able to record an RPM of 66,200 RPM @ 85* F ambient air temperature. This pretty much fixes my fuel delivery problems and will help conserve battery power due to the lower fuel pressure demand.
       I can finally call the GR-7 turbojet engine a completed project!!!!! It only took 4 years and two months to finish :0P

       Now that the engine is complete I can publish some final specifications. Note: These specifications are generalized and for reference only..........

GR-7 Turbojet Engine Specifications

Turbo make: Cummins VT-50 Turbo AR#10076 (From 14 liter 6-cyl. diesel engine)

Turbo inducer diameter: 75 mm

Turbo exducer diameter: 90 mm

Weight of rotating assembly: 3 pounds - 10.5 ounces

Combustor type: Side entry single can evaporative combustor

Combustor metal type: Stainless steel - SAE grade 304

Combustor length - combustor end plate to outside of elbow: 55.88 cm

Combustor elbow inside/outside radius: 52 mm/127 mm

Flame tube ID: 97.3 mm actual (97.5 mm calculated from GR-1 formula)

Flame tube length from evaporator base: 292 mm actual (288.75 mm calculated value from GR-1 formula)

Combustion chamber ID: 147 mm actual (157.5 mm calculated / 7% difference)

Flame tube bypass area: 17.75 sq cm actual (27 sq cm calculated - GR-1 formula not applicable due to evap system modification)

Flame tube hole area: 29.282 sq cm actual (30 sq cm calculated from the GR-1 formula)

Flame tube holes: 112 holes actual (90 holes calculated / 20% difference):

Primary holes: 84 holes @ 7/32” (0.556 cm dia & 0.243 sq cm area for a total of 20.412 sq cm)

Secondary holes: 28 holes @ 1/4” (0.635 cm dia & 0.317 sq cm area for a total of 8.87 sq cm)

Evaporator air induction area: 12.8 sq cm (on injector base’s side)

Evaporator tube inside diameters: 1” x .065” (large tube - 22.1 mm ID) and 5/8” x .065” (small tubes – 12.55 mm ID)

Evaporator tube dimensions: The “trunk” is 11.45 cm long and the “legs” are 7.95 cm long. The outermost part of the legs are 3.8 cm from center of the trunk (radius).

Evaporator tube end-gap to top of injector base: 2.85 cm.

Evaporator tube combined outlet area: 3.71 sq cm

Evaporator base orifice diameter: 19.2 mm

Evaporator orifice pass through area (with nozzle inside): 1.76 sq cm

Oil type: 5-30 synthetic motor oil

Oil pressure: 35 PSI regulated

Hydrostatic oil circulation: 1.1 gallon per minute cold and 1.6 gallons when hot.

Oil tank: 1.6 liters in volume (1.7 quarts)

Total system oil volume: 3.3 liters (3.5 quarts)

Starting system: Twin 400 watt 3-phase starter motors (2 x 1/2 HP)

Starter motor speed: 30,000 unloaded (24,000 under load)

Starter gear ratio: (36 main/26 spur) 1.38:1

System current draw at starting: +/- 85 amps @ 13 volts DC

System current draw while running: 17.5 amps @ 13 volts DC

Fuel type: #2 diesel, kerosene or Jet-A

Fuel pressure: 95 PSI

Fuel consumption: 4 GPH at idle and 13 GPH at full power

Max engine RPM: 66,500 RPM (1450 FPS tip speed)

Idle thrust: 10 pounds static at 31,000 RPM

Full thrust: 51 pounds static at 66,000 RPM

Idle combustor pressure (P2): 6 PSI

Full combustor pressure (P2): 24 PSI

Idle EGT (TOT): 950* F

Full power EGT (TOT): 1200* F

Compression ratio: 2.7:1

Jet nozzle diameter: 72 mm

Gas velocity out of nozzle at full throttle: 1300 FPS

Mass flow at full throttle: 1.33 Lbs/Sec

Engine dry weight: 156 pounds

Engine dimensions (without jet nozzle): 26” long x 18” wide x 20.57” high


Additional Info:

Torque setting of comp. wheel Allen nut: 30 Foot-pounds (24 ft/lbs for stock nut)

Mellet part number for turbine wheel: 1200-050-436

Mellet part number for compressor wheel: 1200-050-428

Possible “bolt-on” sub for VT-50 is Holset HT3B

       I would really like to thank everybody for their support during the construction this project, especially my lovely wife Stacy ;0) I am very lucky to have such a supportive wife that allows me to spend countless hours in the garage without complaint. For that I am one lucky dude :0)
       Thanks as well to all of those who have e-mailed me with encouraging words. You guys have helped remotivate me to get the project finished! For that I am really thankful as I am so glad that the engine is complete. This means that I can move on to the next phase of the project:
The GRV-2 Jet Bike Project!!!!!!

       Please join me again when I start the GRV-2 project for which the GR-7 was intended for. Till then be safe and keep experimenting my friends!!!!!!

Don R. Giandomenico


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