The fuel system installation for the ULPower engine differs from carburettor engines. Whereas a carburettor engine will usually have only one, small diameter fuel line from the fuel tank(s) to the carburettor, the ULPower engine has a closed loop fuel circuit. This means that the fuel line departs from a fuel reservoir to the electric fuel pump which then sends fuel to each fuel injector block on the engine, and the excess fuel is then returned from the engine to the same reservoir where the fuel is drawn from. This is the same setup as in any fuel injected automotive engine.
We highly recommend using fuel lines of sufficient internal diameter to reduce pressure losses to the minimum. See the installation manual.
It is absolutely essential to have a fuel pressure sender connected to the outlet of the fine mesh fuel filter (downstream of the fuel pump) and make sure that the pilot can see the clearly visible and correctly calibrated fuel pressure gauge at all times, showing the (automatically regulated fuel pressure) to be very close to 3bar (43 PSI) under all engine rpm and power conditions.
A full power test lasting at least five (5) seconds should be performed on the ground before each flight to check that fuel pressure remains constant.
In aircraft with one or more wing tanks, it is not always feasible or easily achieved to have a return fuel line to the same tank the fuel has been drawn from. In this case a small "header" tank can offer a solution. A single small diameter fuel line can be used from the fuel tank(s) to supply fuel via gravity to the header tank. (This implies that the fuel inlet at the top of the header tank is lower than the outlet and empty level of the supplying fuel tank(s). The internal diameter and configuration of this fuel line must be sufficient to guarantee sufficient fuel flow to keep the header tank full when the engine is operating continually at full power. It is highly advisable to have a header tank of 3 - 4 liters (+/-1 US gal) so that the fuel temperature in this tank does not rise too much if it happens to be well insulated because the electric fuel pump relies on fuel flow to keep cool. If the header tank is made of metal and can dissipate any heat build up easily, it may be a little smaller in volume.
The electric fuel pump can be switched on or off through a relay (optional extra) which is connected to the ECU and the fuel pump. As a safety feature, and if desired, the ECU can control the fuel pump to stop operating automatically when the engine is not turning. When the ECU is initially switched on, it will turn on the electric fuel pump for +/- 1.5 secs. to build up sufficient fuel pressure and then turn it off if the engine is not being turned over in the meantime. In the case of a crash landing or incident where the engine suddenly stops, the ECU will automatically switch off the fuel pump without any intervention necessary on behalf of the pilot.
On some aircraft the header tank is also the reserve tank. A large diameter fuel line only has to be used from this header tank, onto the pre-filter and then to the electric fuel pump. The large diameter will guarantee minimal pressure losses and sufficient, low velocity, low turbulence fuel flow. We highly recommend employing 10mm (3/8") internal diameter for this section of the fuel line, and 8mm (5/16") internal diameter for the section between the fuel pump, the engine and the return fuel line to the header tank. The standard engine warranty does not cover any damage caused to an engine by insufficient fuel flow/pressure.
Even though electrical fuel pumps are very reliable, many pilots prefer the security of a back-up fuel pump. In this case a second pump, with its own pre-filter,is added in parallel. It is generally commanded manually by a separate switch on the dashboard. (make sure there is a led light indication showing whether it is switched on or off) . Before switching on the ECU , start the back-up pump to check that sufficient fuel pressure can be built up. If ok, switch off the back-up pump. By switching on the ECU, the primary pump is tested.
It is not recommended to run both electric fuel pumps continually. In almost all circumstances only the first pump which is switched on, will actually have fuel flowing through its rotor(regardless whether the engine is operating or not) . As our pumps have a non-return valve on the pressure side of the pump, fuel will not flow through the second pump because their outlets are connected to the same pressurised fuel line. So it will probably not be able to produce more pressure than the pump already operating. This means that the second pump will run with stationary fuel and will overheat because of non-existent or insufficient fuel flow through its internal parts.
For this reason, we recomend to limit the time running on both pumps to critical stages of flight, such as take-off, climb and landing sequences.
(max. 5 minutes)
For a fuel flow of 100l/hr (26.4 USgal/hr) through the closed circuit fuel system.
Fuel lines of:
Internal diameter of 4mm (5/32") result in fuel flow of 2.2 m/sec (7.2ft/sec)
Internal diameter of 6mm (1/4") result in 0.98 m/sec (3.2ft/sec) fuel flow
Internal diameter of 8mm (5/16") result in 0.55 m/sec (1.8ft/sec) fuel flow
Internal diameter of 10mm (3/8") result in 0.35 m/sec (1.14ft/sec) fuel flow