Originally Posted by mm_flynn
For an injected road vehicle, (electronic fuel injection) typically fuel is injected into a point in the intake manifold (or sometimes into the cylinders like aero engines). The amount of fuel injected is set based on the oxygen level in the exhaust to maintain a target mixture. As far as I can tell, this target is a rich of peak target in auto's. The power is regulated by throttling the intake airflow.
Most aircraft piston engines, except new turbodiesel engines use indirect fuel injections into the intake port by means of a continuous fuel flow through the injector. If it would be injected directly into the cylinder, it would require precise timing and amount of the fuel injected, which would almost in all cases require electronically controlled fuel injection - not something you'de see in a 1960 aircraft piston engine design
Rich of peak target in automotive engines is changing nowadays, so in latest VW FSI engines, which use stratified fuel injection, target is quite well lean of peak EGT - comparable with those of diesel engines. But the piston design, valve design and timing (variable) are
much more advanced than your usual Lycontinenal.
Originally Posted by mm_flynn
My understanding of a road diesel is that they always run LOP (except when their airfilter is clogged and they are belching out black smoke)
Modern turbo diesel engines run quite deep LOP at low to medium loads (e.g. while cruising), but if you put the "pedal to the metal", ECU recognises throttle position via the potenciometer as 100% demanded load and adjust mixture to correspond to rich of stoichiometric to achieve maximum available power. You can see that the mixture is indeed rich in the color of exhaust gases, which is almost pure black (unless the car is equipped with diesel particulate filter - I think it's required from Euro IV on) - indication of partially burn fuel in the exhaust - something that wouldn't happen if running LOP.
The simplest explanation for fuel injection in aircraft engine works goes like this. You have an engine without carburettor, but you retain the throttle valve, which allows you to control the mass air intake flow to the engine (of course, you only see the "pressure", not the actual mass flow). The fuel goes from the fuel tanks via the fuel selector to the fuel pump (usually backed up with an electric fuel pump, which can be low-speed or combined low and high-speed). From fuel pump, fuel goes to the fuel manifold (usually on the top of the engine), which then splits the fuel line into smaller lines, one of which goes to each cylinder (4-cylinder engine has 4 outlet ports in the fuel manifold + 1 for controlling fuel pressure). The lines that go from the fuel manifold end up in a fuel injector, which is inserted into the intake port of each cylinder and provides continuous fuel flow when the engine is running. Each injector is supposed to be (at least TCM and Lycoming say so) tuned so the fuel flow from the injector matches the air intake flow through each intake port, but in reality they are usually quite far off (unless you have GAMI injectors). The fuel flow through the fuel injector depends on the throttle and mixture position if you have TCM engine, which basically means: full throttle and full rich mixture (takeoff power) = maximum fuel flow. If you use Lycoming engine, the thing gets a bit more complicated, since the injectors try to adjust for increasing altitude and thus reduced air pressure and density by "comparing" air and fuel pressure, but it's far from what one would consider optimum - if you climb with all three levers forward, the Lycoming engine would still run richer and richer and the TCM engine would be just a bit worse.