Before gasoline can burn in a piston engine it needs to be vaporized and mixed with oxygen in the right quantities. This process is done by either a carburetor or by an high pressure injection system. For this process to be as perfect as it can be the system needs to take into account, power setting, mixture control and such.
Piston powered aircraft engines can use either a carburetor or a modern injection system, our previous page talked about the basic float carburetor, here we will dive into the fuel injection system used on high performance aircraft engines, both gas and diesels; although these system are not alike.
These injection system do not suffer from ice formation on the throttle valve and have a number of other advantages warranting their higher cost of installation.
With an injection system fuel is pressurized and introduced just ahead of the inlet ports, directly in to the combustion chamber (GDI, gasoline direct injection) or at the super/turbocharger impeller. Normal carburetion uses a pressure differential to vaporize the fuel before it enters the cylinders.
There are two types of fuel injection systems in use, these are continuous flow and direct injection. We will describe both of them here.
This system provides a continuous flow of pressurized fuel at each inlet port of the cylinders and basically it uses the following parts:
Super- and turbocharged engines can also use a fuel injection system but they will need modifications to adjust the fuel flow with rapid throttle openings combined with air pressure sensors in the manifold. Introducing more air should mean more fuel (and power) if the engine is to run smoothly without faltering when opening the throttle.
With this system fuel is pressurized and injected directly into the combustion chamber bypassing the inlet valve, much like a diesel engine but with the two spark plugs. It is used on higher powered engines mainly.
This system uses almost the same parts as described above with the continuous flow fuel system with the only difference the point where the fuel is being injected.
As with any system there are always two sides to the picture. Fuel injection can provide each cylinder with the correct fuel air mixture for the operating conditions at that particular time where carburetors supply the same fuel/air mixture to all cylinders at once. This could mean that one cylinder could run cool where others run possibly hot. Which is why you need CHT sensors on all cylinders.
Summarizing the advantages:
Some disadvantages are:
To conclude: fuel injection systems maybe more expensive initially but they will save fuel and prolong engine life thus saving on maintenance cost and increase engine reliability and safety for those involved in the flight. As such the advantages are something to think about!