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ULPower, FADEC Design

Formed in 2006, ULPOWER Aero Engines is a small Belgian company which started as a joint venture by a number of individuals and companies. Their intention is to develop and manufacture a light weight aero engine where power and reliability is priority number one.

FADEC stands for Full Authority Digital Engine Control. In the case of ULPower it means that the ECU (Engine Control Unit - digital computer) controls all aspects of engine operation and decides on the timing and amount of fuel it injects into the inlet ports as well as the exact timing of the spark advance.

A very important advantage of computerized fuel injection is that it fully eliminates the risk of carburetor icing, as there is none! According to the General Aviation Safety Council in the UK, carburetor icing causes on a yearly average 6 to 10 accidents with serious injuries or fatalities (in the UK alone!).

FADEC design decisions

The FADEC system automatically sets the fuel mixture and ignition timing for optimum performance at any given operating condition.

Unlike a carburetor, which is tuned/set for just one condition, fuel injection controlled by FADEC adapts the fuel mixture to every different operating condition. Because the amount of fuel that is injected into the inlet ports is electronically controlled, the fuel/air ratio will be much more appropriate at any given time and the overall fuel consumption will be less (anywhere up to 15 - 20 % depending on how 'bad' your carburetor is set).

ECU Operation

The ECU has a complete 3D map programmed into it so it can decide on how long each injector needs to be open to get the correct amount of fuel through in all different circumstances. Looking at RPM and throttle position the ECU calculates (multiple times per second!) the amount of air going into the engine and sets the injector timing accordingly (depending on the programmed figures). Our FADEC unit will even fine tune the fuel flow to compensate for changes in barometric pressure as well as inlet air temperature in the inlet collector!

The higher the aircraft goes, the more the barometric pressure drops so less fuel will need to be injected. When the inlet air changes (not only differences in hot or cold days, but also as the aircraft climbs) the amount of fuel will be adapted. The hotter the air, the less dense the air is and so less fuel is needed to retain the same fuel/air mixture and run in optimal conditions.

ULPower Spare PartsULPower Spare Parts

Completely variable ignition timing sets the spark advance at the ideal point in every situation. Needless to say this will be better for engine operation as opposed to a fixed (magneto or even CDI) advance that has been set to an average figure of eg. 22° (a tradeoff between low advance for starting and more advance at higher RPM and power levels).

Another advantage of a fuel injection system is that each cylinder has its own fuel injector, making sure the amount of fuel is equally distributed over all cylinders. This results in equal power production in all cylinders and as such a smoother running engine. In a carburetor engine there is the chance of having one cylinder running too rich and the other too lean because there is little way of controlling how the fuel gets mixed with the air and which way this mixture prefers to go due to variations in the airflow pattern inside the inlet manifold. A cylinder running too lean (high exhaust temperatures) can cause severe damage to an engine (and even bring it to an immediate standstill) if it starts to "knock".

Since the ECU is completely (factory) programmable they can for example, make the engine run cooler on idle by making the mixture richer because vaporization of the excess fuel in the cylinders takes away a lot of the heat. Since the engine isn't using much fuel on idle anyway, the slightly increased fuel consumption at idle will not hurt your wallet but will be better for your engines overall life time.

Easy starting

As in any modern automobile today, just press the start button and it goes! There is no need for priming or manually applying choke for startup and during warmup of the engine. A dedicated oil temperature sensor will 'sense' if the engine is cold and will automatically enrich the mixture accordingly for easy starting. The choke function will gradually fade out as the engine warms up. The variable ignition timing will also aid starting in cold conditions. The engine is set to a 10° starting advance after which it will advance more and change continuously depending on the operating conditions.

Vapor Lock

The design of the fuel system eliminates the chance of vapour lock at startup. Because it is under pressure, vapour lock will not easily occur and if it does, it will be 'flushed' through the system as fuel is pumped through the engine before startup, when the pump switches on. As the injectors are right near the 'loop' of fresh fuel circulation the whole system is flushed, unlike many other fuel injection systems that have 'dead end' lines to the injector nozzle. This practically guarantees the engine will start and restart at every attempt (hot or cold).

Text and images used with permission of ULpower.

Written by EAI.

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