ULPower engines: Advantages of fuel injection and FADEC

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

Eliminating the disadvantages of a carburettor

A very important advantage of fuel injection is that it eliminates the risk of carburettor icing, as there is no carburettor! According to the General Aviation Safety Council in the UK, carburettor icing causes on a yearly average 6 to 10 accidents with serious injuries or fatalities (in the UK alone!).

Carburettor ice occurs due to the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburettor. If water vapor in the air condenses when the carburettor temperature is at or below freezing, ice may form on internal surfaces of the carburettor, including the throttle valve. The reduced air pressure, as well as the vaporization of fuel, contributes to the temperature decrease in the carburettor. Ice generally forms in the vicinity of the throttle valve and in the venturi throat. This restricts the flow of the fuel/air mixture and reduces power. If enough ice builds up, the engine will suddenly stop with little or no warning! Carburettor ice is most likely to occur when temperatures are below 20°C (70°F) and the relative humidity is above 80 percent. However, due to the sudden cooling that takes place in the carburettor, icing can occur even with temperatures as high as 38°C (100°F) and humidity as low as 50 percent. This temperature drop can be as much as 20°C (70°F)!

As a preventive measure against carburettor icing, one can apply carburettor heat. It is an anti-icing system that preheats the incoming air before it reaches the carburettor. Carburettor heat is intended to keep the fuel/air mixture well above its freezing temperature to prevent the formation of carburettor ice. However, there is a disadvantage to its use: the use of carburettor heat causes a decrease in engine power (sometimes up to 15 percent!), because the heated air is less dense than the outside air that had been entering the engine. This also enriches the mixture as the carburettor does not compensate for air temperature.

In most carburettored engines, the air/fuel mixture going through the inlet system is also heated again to aid the vaporisation of the fuel droplets 'sucked' out of the nozzle in the carburettor. As a cold engine reaches normal operating temperatures, it looses horsepower due to the difference in air density. A fuel injected engine has its fuel injected in the inlet manifold under pressure. This causes a very fine mist of fuel that doesn't need heating to evaporate. As there is also no need to heat the air against possible icing, the fuel injected engine will keep it's horsepower so it can be used efficiently!

An other disadvantage of most carburettors is that the fuel bowl can flood. As a result fuel can overflow outside of the carburettor body into the engine compartment! This is a significant hazard as there is a danger of petrol leaking onto a hot engine or exhaust and potentially start a fire or cause an explosion! Often a drip tray is used to collect the spilt fuel and eventually route it outside of the aircraft. Needless to say that modern technology fuel injected engines do not have this problem and will be safer and cleaner as a result...

Running in optimal conditions is better for fuel consumption and your wallet

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

Unlike a carburettor, that is tuned/set for just one condition, a 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% depending on how 'bad' your carburettor is set).

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 right 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.

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 trade-off between low advance for starting and more advance at higher rpm and power levels).

Another advantage of the UL260i 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 a smoother running engine. In a carburettored engine there is a risk 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 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 we can for example, make the engine run cooler on idle by making the mixture richer because vaporisation 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 won't hurt your wallet but will be better for your engines life.

Easy starting makes life easier

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 start-up and during warm-up of a UL260i engine. A dedicated oil temperature sensor will 'sense' if the engine is cold and will automatically enrichen the mixture accordingly for easy starting. The choke will gradually fade out as the engine warms up. The variable ignition timing will also aid starting in cold conditions. Our engine is set to a 10° starting advance after which it will advance more and change continuously depending on the operating conditions.

The design of our fuel system eliminates the chance of vapour-lock at start-up. Because the fuel system 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 start-up, when the pump switches on. As our injectors are right near the 'loop' of fresh fuel circulation the whole system is flushed, unlike many other fuel injection systems (as shown on the right) that have 'dead end' lines to the injector nozzle. This practically guarantees the UL260i engine will start and restart at every attempt (hot or cold).

Single lever control - less pilot workload and more comfortable/enjoyable flying

FADEC reduces a pilot's engine management tasks to simply selecting the desired power setting through a single control. You can now forget about managing the engine and focus on flying. You must admit that the recreational pilot doesn't really want all the hassle, but just wants to enjoy flying. With just the throttle to adjust, there is certainly less risk for the pilot (and certainly less experienced ones) to forget something (for example applying carburettor heat) or do something wrong such as flooding the carburettor on start-up or leaning it too much and possibly damaging the engine.

The precise and immediate reaction of the FADEC to any change in engine operation results in better throttle response, stable rpm and lower fuel consumption; a feature all pilots will appreciate.

Easier and cleaner installation

As the ECU is factory programmed, the whole installation is just a matter of plug and play. Forget about fiddling around with the carburettor needle to try and get the jetting and idle rpm right. You can certainly eliminate all the hassle of synchronizing carburettors (and keeping them in sync) if you have 2 carburettors installed on an engine such as on the Rotax 9-series.

Since the UL260i is single lever controlled, there are less cables to install and the usual heat box for the carburettor heat can also be eliminated. Less knobs/handles also give a cleaner dashboard as a result.

Extra safety features

Something that can't be achieved with a carburettor is that the UL260i engine controlled by its ECU has a built-in electronic rpm limiter that protects the engine from over revving. People experimenting with the pitch on a (ground adjustable) variable pitch propeller, accidental engine starts without a propeller, or even propellers disintegrating in flight can all be reasons why an engine could unintentionally over rev and cause severe internal engine damage.

Another safety feature built into our ECU is that it controls the electric fuel pump. If the engine stops, it will shut-off the fuel pump automatically. This is not only done so the pilot can't forget to switch it on/off, but primarily to reduce the risk of fire in the event of a crash. If the fuel would not be shut-off immediately, fuel leaks and continuing fuel circulation under pressure could cause fire and the hazard of explosion.

With single lever control and FADEC taking care of all of the engine management tasks, the risk of pilot error is much reduced. As human error is still large factor in many accidents we believe the UL260i FADEC controlled engine will increase safety in general in any powered aircraft.