The Rotec TBI Fuel System, is the most compact and simple throttle body injector on the market. Its unique fuel distribution system makes it easy to setup and operate. With excellent power per volumetric flow, smooth mixture control, and a variety of models to suit any engine, the system is a must for any serious experimental pilot.
Fuel delivery and pressure are controlled by the “on demand” fuel pressure regulator, supplying the precise amount of fuel needed to the engine. This system is truly self regulating, and is not effected by fluctuating fuel levels or pressures.
Greater performance and economy is a result of the ultra fine fuel atomisation when compared with regular carburettors. The superior air fuel mixture and reduction of mixture temperature results in a more efficient fuel combustion.
With the TBI’s use of a slide throttle, as opposed to a butterfly valve, the total wetted area and drag is reduced, resulting in a greater throat area for the same size bore.
Another advantage of a slide throttle is that unlike the butterfly valve, the fuel mixture is not deflected into the side walls of the inlet track where the mixture tends to accumulate and the benefit of fuel atomisation is lost.
The TBI can run a wide range of fuel pressures, from 0.5 to 6.0 psi, even be gravity fed. The TBI is not attitude sensitive as it has no float chamber and so consequently is fully aerobatic. Starting the engine from cold is simply a matter of pressing the diaphragm override button on the TBI regulator while cranking, which gives the engine a squirt of fuel to start.
Idle speed is set via typical throttle aperture stop and bypass mixture screw which sets the idle fuel mixture. The slide throttle and mixture levers are controlled via typical Bowden push pull cables. The air cleaner side of the TBI is of the standard aviation four bolt flange, designed to fit the standard range of aviation air intake ducting & filters.
How the Rotec TBI Works
The Rotec TBI Fuel System uses a spray bar positioned in the intake air-stream. The venturi effect is utilized to draw fuel out of the spray bar as required.
The simple, yet incredibly effective fuel regulator (see Figure 2) is connected to the fuel inlet of the TBI. Fuel pump pressure on the inlet side of the regulator is blocked by a flow valve. This valve can only allow fuel to flow when the diaphragm experiences a drop in atmospheric pressure at the spray bar. The degree to which the valve opens depends on how much air passes the spray bar.
The clever part is that the incoming fuel pressure at the regulator aids in the closure of the fuel flow valve. Consequently fuel pressure and the negative pressure created at the spray bar are always balanced. Altering the fuel pressure will have no effect as the balance will adjust automatically to match the exact fuel demand the engine requires for any given power setting. It is effectively a negative pressure regulator.
This principle is also used in scuba diving equipment. When a diver draws a breath, the respirator creates a small negative pressure on the diaphragm and the flow valve opens; but, on the other side of the flow valve is an oxygen tank with very high pressure. Why does this pressurized air not blow up the diver’s lungs? Because as soon as the diver draws breath the diaphragm opens the flow valve. This in turn exposes the tank pressures to the diaphragm and instantly tries to close the flow valve. Therefore as the diver draws a breath, the diaphragm allows only the air required.