[RLWP]

(Professor Powell mounts the rostrum. An awed hush falls)

Ahem. Consider the modern fuel injection system as used in an automobile. It has several components. An injector that squirts the fuel into the inlet manifold. A fuel feed to the injector. An electrical harness to trigger the injector. A throttle to control the airflow to the engine (and vary the compression ratio(see previous lecture notes)). A mass flow meter to measure the air delivered to the engine. An electronic control box.

The air entering the engine is controlled by the throttle and measured by the mass flow meter (usually by a volume flow meter and a temperature sensor). The throttle position and the mass flow rate is fed to the control box together with an indication of the crankshaft position. The control box uses an electronic "map" to decide how long each injector should stay open to deliver the correct quantity of fuel for the air being used. It the fires each injector in turn at the correct time relative to the crank position. When the injector opens it allows fuel from the feed line to pass into the inlet manifold. The fuel is maintained at pressure by a fuel pump and a regulating valve that spills fuel back to the tank. In addition more modern control boxes will control the ignition system as well.

Let us consider which of these components we would like to fit to the moving part of our rotary and which to the stationary.
The injector. This could easily be fitted to the moving part.
The fuel feed. Apart from making the two connections between the moving and stationary parts this could be fitted to the moving part.
The trigger harness. We need at least one wire to fire each injector. This means several wires. If the control box is on the moving part, we have no problem. If the control box is on the stationary we have to make a multi way connection between the stationary and fixed parts of the engine. Difficult!
The throttle. Ideally we would like only one of these. If this is on the stationary part it could be controlled by a simple cable. However air leaks in the air circuit between the throttle and the inlet valves must be minimised. If it is on the moving part we need a means of varying its opening to control the engine.
The mass flow meter and control box. If mounted on the stationary part we must pass a multi wire harness across to the moving part. If mounted on the moving part we must pass a multi wire harness across to power them.

The simplest conceivable method of using fuel injection is to have a single injector on the staionary part of the engine. This would be on a manifold that feeds across to the inlet manifold on the moving part. Any other configuration means multiple moving connections of wires and fuel pipes. And if we only have a single injector you might just as well use a carburettor mounted on the crankshaft feeding into the crankcase. Now where have I seen that before?

( Professor Powell turns an leaves the stage, to the accompaniment of a bemused silence...)

Richard

Don't forget that one of the main drawbacks of a rotary is that most of the engine is spinning round. Go and open the bonnet (hood) of your car and see how many wires pass from the bodywork onto the engine!