The ULPower engine designers have given a lot of thought to the question of where and if, to build in redundancy. In general, it is either impossible or impractical to duplicate the functions of most of a piston engine's mechanical or electric components. Since reliability carries such importance in aircraft engines, components which are specifically designed for the engine are given large factors of safety whenever possible to reduce the risk of failure to the minimum.
UL Power engines have incorporated dual spark plugs on each cylinderhead.
The ULPower engine needs to have four separately controlled ignition coils, each of which has an output to two different cylinders. This are the so-called "Distributorless Simultaneous Ignition Systems" which have one ignition coil with two spark plugs wires for two cylinders. This means that each coil will need to fire simultaneously to two separate cylinders.
On cylinder nr. 1 the spark will be generated by coil nr. 1 to spark plug nr. 1 to ignite the compressed fuel/air mixture. Coil nr. 1 will also generate a spark to spark plug nr. 5 on cylinder nr. 3 but the spark will be "lost" (waste spark) because cylinder nr. 3 is at the top of the exhaust stroke.
Coil nr. 2 will generate the spark to spark plug nr. 2 of cylinder nr. 1 to ensure ignition if spark plug nr.1 and/or coil nr. 1 fails, and also to spark plug nr. 6 of cylinder nr. 3 during the exhaust stroke. The logic is the same for the remaining ignition configuration. If the "waste spark" method is not used, then eight separately controlled ignition coils would be needed to ensure redundancy, at considerably higher weight and expense.
As the ULPower engine uses a multipoint fuel injection system, we could argue that fuel injection has some form of redundancy. Each injector provides fuel to one cylinder. So if, for any reason a fuel injector would fail, the engine would continue to run on the remaining three cylinders. Although the engine would have a significant power loss, the aircraft will still be able to continue flying while in search of an airport for a precautionary landing.
Although the ECU has never been the direct cause for the engine failure of any of DR Tuning's auto sport clients in more than 15 years of operating in tough conditions, a short circuit in a fuel injector has once caused a steering fuel injection relay to fail. Since only one steering relay was used for the simultaneous pulse to all fuel injectors, the short circuit of one fuel injector caused the stoppage of the other three. The end stage for the electronic steering of the fuel injectors in the ECU has now been increased from one in the auto version to four for the aeronautical version so that each fuel injector has its own dedicated steering circuit.
Optionally we will also offer engines which can accommodate two fully redundant ECU units and their respective pulse pickup sensors. Both units will have simultaneous control over all four injectors, and each unit will steer two ignition coils. In the highly unlikely event of a failure of one ECU unit, the other still has full authority over the engine.
We offer 3 possibilities of redundancy, see here.