Lycoming IO360 - relationship between throttle position and fuel flow?

[Contacttower]

Can someone give me some detail on the fuel flow system on the Lycoming IO360 and how throttle position controls fuel flow?

My understanding is that since it is a fuel injected engine the throttle valve is just controlling air flow into the engine and the fuel is added by the injectors after the air has gone through the valve. What controls fuel flow though? Is it an air mass sensor that detects the amount of air let in by the throttle valve and adjusts fuel flow or is the throttle position just mechanically linked to the injectors?

For example when priming before start up the throttle needs to be open in order to let fuel flow in...how is the throttle linked to the fuel control though?

[riverrock83]

From the manual (http://www.7ts0.com/manuals/lycoming/360/O-360-HO-360-IO-360-AIO-360-HIO-360-TIO-360_OM.pdf):

The Bendix RSA type fuel injection system is based on the principle of measuring air flow and using the air flow signal in a stem type regulator to convert the air force into a fuel force. This fuel force (fuel pressure differential) when applied across the fuel metering section (jetting system) makes fuel flow proportional to air flow.

There are other options, but most use the system above.

[phiggsbroadband]

So if you pull into a climb, leaving the throttle fixed, the revs will drop from say 2500 to 2200. This means less air sucked in, and so less fuel used.

Hence the fixed throttle is not controlling a fixed rate of fuel used.

I think the same would happen in a carburettor engine as the fuel is sucked through the main jet by venturii action. (again proportional to air flow.)

[Pilot DAR]

So if you pull into a climb, leaving the throttle fixed, the revs will drop from say 2500 to 2200

I cannot think of any application of an IO-360 with a fixed pitch prop, so no, the RPM will not reduce, The prop will reduce pitch to maintain RPM

[flyinkiwi]

I cannot think of any application of an IO-360 with a fixed pitch prop,

Erm, 172R?? :p

[Contacttower]

OK so it is controlled by air mass flow.

The gap in my understanding though comes when considering priming the engine - if it is just air flow that controls fuel flow, how come when you prime the engine the throttle needs to be open? Just opening the throttle surely isn't going to create an airflow into the engine because when it is shut down there is nothing to draw the air through. How does the fuel system 'know' that the throttle is open and therefore allows fuel to flow when you turn on the electric aux/priming pump when priming?

[It flies]

I cannot think of any application of an IO-360 with a fixed pitch prop
Erm, Pitts S-1S? :p

[mmgreve]

I happen to fly two different planes both equipted with a IO360. In one application the throttle should be open during priming, but in the other it should be closed.

When I at times have confused the two, it has made absolutely no difference if the throttle was open or not.

[srayne]

Can someone give me some detail on the fuel flow system on the Lycoming IO360 and how throttle position controls fuel flow?


Here's how it works (http://www.precisionairmotive.com/Publications/15-812_b.pdf)