As far as I know in a car engine the ECU can adjust fuel mass flow through every injector. I don't know the exact algorithm but probably engine roughness is monitored. Of course this is not possible in a jet engine. What will happen if an injector starts to malfunction? I assume it will be quite difficult to detect and a slight decrease in maximum power will appear. But engines usually are not run at full power? Can this be dangerous when maximum performance is needed (like engine failure at V1)? How are injectors tested in engines with mechanical fuel control? Can FADEC monitor fuel injectors?

  • $\begingroup$ Car engine ECU's use a few sensors to adjust fuel flow. One is the MAF (Mass Air Flow) or MAP (Manifold Air Pressure) and the other is the Oxygen sensor in the exhaust stream. Combined with other engine data (RPM and throttle) an injector timing (opening time of the orifice) is calculated from a 3-D lookup table programmed into the ECU. This is significantly different from how jet engine fuel injection systems work. Jet engines don't have cycles, so its a continuous flow system. $\endgroup$
    – Ron Beyer
    Feb 11 '16 at 22:22
  • $\begingroup$ I know that but I was talking about different think. Car ECU can try compensate for individual injector wear or different calibration and try to compensate accordingly. $\endgroup$
    – Andrius
    Feb 12 '16 at 6:28
  • 2
    $\begingroup$ According to the AgentJayZ YouTube channel, which has videos of fuel nozzle testing, the injectors are not the same as those in a car. A car's injectors open and close in response to an electrical signal. The fuel nozzles in a jet engine are just nozzles, with no moving parts. The fuel flow to the engine is regulated by adjusting the fuel pressure. $\endgroup$
    – Steve
    Feb 12 '16 at 13:09
  • 3
    $\begingroup$ "Car ECU can try compensate for individual injector wear or different calibration and try to compensate accordingly" No, it really doesn't, there is no "injector wear compensation" in an ECU (I've written ECU software). It works on timing tables. The injectors are opened for some period of time using a PWM signal based on the sensors I mentioned. It can't compensate for wear or even knock (which is why a knock sensor produces a check-engine light). There is no way for the ECU to measure how much fuel each injector is providing, its based off of factory calibration. $\endgroup$
    – Ron Beyer
    Feb 12 '16 at 14:17
  • $\begingroup$ I've never worked on a turbine that had any sort of monitoring of injector/atomizer performance. I suppose that in theory it could be possible to do so by monitoring fluctuations in fuel flow, but the aircraft I worked on never had anything like that. $\endgroup$ Oct 1 '16 at 21:01

Fuel nozzles are overhauled and bench tested to meet the manufacture's operational limits. They are controlled for both flow (back pressure) and also flow pattern. The FADAC monitors fuel flow, this along with the compressor vane position are the main input controls for thrust generation.

The fuel nozzles do degrade during engine's operation. This contributes to the engine running hotter as it ages. Other contributors are the erosion of the compressor hardware and the burning/oxidation of the combustion chamber and turbine hardware. In fact a defective fuel nozzles may lead to a "hot spot" that accelerates the burning/oxidation of the combustion chamber. The FADAC and flight crew will monitor the throttle response and also the Exhaust Gas Temperature (EGT) as the controls to understand the relative health of the fuel nozzles. If the engine exceeds the EGT limit a mandatory boroscope inspection is required to keep the Aircraft in service, this inspection will visually verify the condition of the fuel nozzles and combustion chamber.


Yes a FADEC can monitor fuel flow.

Let's assume you are operating a simple turbine. Normally you will have fuel flow, turbine speed and if a turboprop a torque monitor. The pilot monitors each of the steam gauges. The fuel control unit will normally limit max fuel flow.

An ECU is more akin to a FADEC, and the range of programmatic control in a FADEC is diverse, so a generalization is not as easy as in a simple turbine.

So to summarize, Yes, a FADEC can monitor fuel flow (and everyone I am familiar with does). And in the case of a more simple turbine application, the pilot, and the fuel controller (which will vary in implementation) can also provide limits.

  • $\begingroup$ The question is asking about individual injectors, not total fuel flow. $\endgroup$
    – Ralph J
    Apr 2 '17 at 20:37
  • 2
    $\begingroup$ @RalphJ … and since the injectors are just fixed nozzles, total flow and pressure is all you really need to know. $\endgroup$
    – Jan Hudec
    Apr 2 '17 at 20:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.