Turbitrac
Designed and built by Gary Packham
Turbitrac started life as a propane burning engine when I built it in 2005, and had the addition of a diesel after burner shortly before I converted the engine to run on diesel also. The engine still starts on propane and this is achieved by supplying propane direct from the bottle without a regulator. The gas (bottle need not be inverted) enters the Combustion Chamber (CC) via the evaporator system. The gas enters and mixes with the air stream to the evaporator, from an open pipe (no jet). A portion of the air being supplied from the compressor is ducted around to the end cap of the (CC). This is where the gas enters and is taken by the air flow through a set of six swirl vanes and into the evaporator cup, this inverted cup has a back plate that will be heated by the burning gas once it is ignited. The cup is sealed to the end cap except for a series of small holes around its outer sides. As the gas exits the small cap holes it is ignited by a spark, you hear a loud pop as this happens. You now have a spinning compressor supplying air that is also being mixed with gas making its way through the evaporator system and being ignited when it exits the evaporator cup. This burning gas is heating the back plate of the evaporator cup but is also expanding the air in the (CC) by heating it. This hot expanded air forces its way through the turbine causing it to spin faster. As the turbine picks up speed so to will the compressor wheel as they are on a common shaft. As the compressor wheel gets driven faster more air is compressed into the (CC), more air and fuel means more heat and more RPM on the common shaft. Idle speed on the Turbitrac is about 30,000 RPM and after running for just a few minuets the evaporator cup back plate will be glowing. Now the fuel pump can be switched on and the needle valve opened slightly. Fuel is delivered through a stainless steel thin wall pipe just in front of the six swirl vanes where it is mixed with the turbulent air exiting the vanes. The volume of fuel being delivered is controlled by squashing the end of the pipe in a drill so it ends up with three flat segments. This "jet" is further fine tuned so that fuel delivery is in the region of 5 gallons per hour. This crude spray pattern allows partial mixing of the fuel with the air until it all hits the hot glowing back plate. At this point the fuel is evaporated and exits with the air through the small holes in the cup. As the evaporated fuel is ignited by the burning gas you notice an increase in speed of the turbine. Careful control, reducing the gas and increasing the fuel will keep the engine RPM stable until the gas is turned off. At this point the gas can be taken away and the spark turned off. The temp of the gas exiting the turbine changes as the speed of the engine changes. As the revs pick up the TOT's will become lower and then will start to increase again as you approach your max RPM. This can be used to help you light the after burner which can sometimes be difficult to get alight. You need the AB for max thrust but trying lighting it half way through your rev range may not be hot enough. I use 30-40% petrol in my AB fuel to ease lighting but I also drop the revs for an instant and then quickly increase them as I switch on the AB pump. This slower speed hotter gas exiting the turbine ignites the AB fuel with a real big bang but may have to be repeated a couple of times until the AB is hot enough to sustain the flame. This is demonstrated on the Turbitrac night video.
I am currently making changes to the oil pump system and will be testing a new design soon. I have built new steel fuel tanks, the engine fuel tank is 300 X 300 X 200 with a submersible high pressure pump and the AB tank is 300 X 300 X 300 with two external high pressure pumps. When run, both tanks should empty at the same time. I also have a hand held tachometer so that I can match max revs to a pressure reading on my P2 gauge. This means I can run the engine to max RPM and then take a P2 reading which will be my max pressure for that day, and run without a tachometer for the rest of the day. This is only a cost issue, the hand held tachometer cost me £20 and a fixed system is in the region of £200.