gruntguru wrote: ↑
Fri Mar 31, 2017 4:24 am
Probably a more interesting question is "what role does air flow play in regulating the output of these engines?
Driver's foot demands a change in torque output. Butterfly valve(s) adjsut to change airflow to engine. ECU senses any change in airflow and/or MAP and/or Throttle position and adjusts fuel quantity to maintain best-power AFR.
Driver's foot demands a change in torque output. ECU immediately adjust fuel quantity to match the torque demanded. (This is possible under most conditions because the engine is running in a highly-excess-air state and more fuel will produce more power - instantly). At the same time the ECU will adjust butterfly valves and/or MGUH output to bring the MAP and exhaust-backpressure (and therefore air flow) to the most efficient levels for the new fuel rate.
So airflow plays a slightly less critical role in the current lean-burn ICE.
BTW. Sensing exhaust-backpressure would also be essential.
I would expect the control strategy to be similar to what is normally used with diesel engines these days. Pedal position is translated to a torque request using pedal maps and engine speed and from this torque request the fuel mass that needs to be injected can be calculated. Fuel limits based on how much air the engine currently consume prevent the engine from going too rich. Airmass can be calculated using either speed-density or alpha-n with density correction, and given that F1 engines favour individual throttles I would expect alpha-n to be used; that is throttle position and engine speed as the main inputs to the airmass flow calculation model and using the density of the air in the plenum as the main correction. An airmass meter isn't required, and not really desirable either as they have a sluggish response during transients, restricts the airflow to the engine and can be fooled by pressure pulsations (caused by for instance compressor surge).
Once the injected fuel mass have been calculated, it is possible to calculate how much air the engine need to burn that fuel optimally, which is then achived by adjusting throttle position and boost pressure until m_air_actual = m_air_req. This is basically how any modern diesel engine works except for the use of airmass meters as the main input for airmass flow (usually using speed density as backup in case of MAF malfunction or during transients to improve response).