Gill fuel flow sensor failure modes

[autogyro]

Looks to me that RB has used the unreliability of the fuel flow sensor to gain a power increase in an attempt to address their problems of having less power and less control over that power than other teams and power unit suppliers.

This is false. FIA mandated the use of the original 'unreliability of the fuel flow sensor' before the race.

Brian

False?
RB refused to abide by the FIA ruling.
By using a different source of data for their fuel flow, RB ensured the lowest possible fuel flow reading.
Readings at the injectors will give a totally different and lower fuel flow, allowing more fuel into the engine.
That is an absolute power benefit.

[Jef Patat]

Readings at the injectors will give a totally different and lower fuel flow, allowing more fuel into the engine.
That is an absolute power benefit.

Did you read the last couple of pages? Several members have stated that an ECU can make a quite accurate estimation, with several arguments to back that up. Why do you say the readings will give a lower consumption?

That is not to say RB might have played a bit with those estimations to better fit their reality and might give a lower consumption.

[alexx_88]

I'd love to see evidence of an ECU calculating the fuel flow over a short enough period of time to be considered instantaneous with an accuracy of 1% as is the one stated by Gill and without any correction factor programmed into it. It boils down to the question: if you put a 1ms pulse over a 10cc/second injector, do you get exactly 0.01cc of fuel each time?

What I bet is that, all the engine manufacturers have correction factors on the simple math that is SUM(injector_pulse_width * injector_size) which yield, for that engine a more accurate fuel rate value. The FIA needed the same measure tool for all, thus the the flow sensor. If every team gets 10 of them, tests them and uses the one which they like most (reads the lowest) then it's a level playing field.

[hardingfv32]

Why the concern about ' instantaneous' fuel flow readings? There is nothing in the rules specifying the time period that applies to the measurement of the specified fuel flow. Seems like a very simply written rule which I assume was drawn up by the manufactures. Is there a reason for such a simple fuel flow rate rule?

Brian

[Physicist2]

It was just brought to my attention that the FIA specified the low-pass filter to be implemented in the flow sensor to be a 4th order Butterworth. The Butteworth would be a very poor choice for this application, as it suffers from serious overshoot and ringing in its time domain response to a step function input (A Bessel filter would be a much better choice.) If that is indeed the filter they are using, filter ringing may well be contributing to the reported problem of "spikes" or "noise" -- and reducing the corner frequency from 10Hz to 5Hz would make that problem worse rather than better. I find it hard to believe sharp-eyed engineers from the teams have not flagged that problem. Does anyone have information on whether the low pass filter being used is in fact a Butterworth?

http://www.fia.com/sites/default/files/ ... eter_0.pdf

[langwadt]

I'd love to see evidence of an ECU calculating the fuel flow over a short enough period of time to be considered instantaneous with an accuracy of 1% as is the one stated by Gill and without any correction factor programmed into it. It boils down to the question: if you put a 1ms pulse over a 10cc/second injector, do you get exactly 0.01cc of fuel each time?

What I bet is that, all the engine manufacturers have correction factors on the simple math that is SUM(injector_pulse_width * injector_size) which yield, for that engine a more accurate fuel rate value. The FIA needed the same measure tool for all, thus the the flow sensor. If every team gets 10 of them, tests them and uses the one which they like most (reads the lowest) then it's a level playing field.

It is direct injection so 1 ms is a long time, the whole compression stroke at 10krpm is 12ms
the flow through the injector will depend on the differential pressure, so will opening and closing times and it direct
injection so it isn't just fuel pressure vs. ~1bar like manifold injection it is fuel pressure vs. cylinder pressure
opening time will also depends on the voltage driving the injectors.

And I don't see why the teams, other than for the flow restriction, need an absolute flow flow number, they need
injections to be consistent so the engine can be tuned to the correct mixture

[DaveW]

It was just brought to my attention that the FIA specified the low-pass filter to be implemented in the flow sensor to be a 4th order Butterworth.

A good find, & your argument is correct. The difficulty is, the precise details of the device are not disclosed. Perhaps we will find out more when RB's defense is published.

In the mean time two other extracts from your reference bother me:

The device shall be able to recover automatically and without action from an incorrect fluid composition (Air bubles for example). I guess they mean "bubbles", that are likely to be found in any agitated fluid system..

When unable to read flow the device must store the last correct data and count no flow until it is able to measure flow again. That statement raises all sorts of (potential) issues. (I don't have a failure mode... I just output junk data).

The mind boggles....

[Physicist2]

It was just brought to my attention that the FIA specified the low-pass filter to be implemented in the flow sensor to be a 4th order Butterworth.

A good find, & your argument is correct. The difficulty is, the precise details of the device are not disclosed. Perhaps we will find out more when RB's defense is published.

In the mean time two other extracts from your reference bother me:

The device shall be able to recover automatically and without action from an incorrect fluid composition (Air bubles for example). I guess they mean "bubbles", that are likely to be found in any agitated fluid system..

When unable to read flow the device must store the last correct data and count no flow until it is able to measure flow again. That statement raises all sorts of (potential) issues. (I don't have a failure mode... I just output junk data).

The mind boggles....

The requirement that the filter be a 4th order Butterworth filter is specific enough to know that it will cause transient overshoot and ringing, irrespective of other details of implementation. Unless that specification has been changed or over-ridden, the filter is almost certainly contributing to "spikes" that have forced teams to dial down their max. fuel flow. Other things could cause a problem, this likely is contribution to a reported problem. And I don't think this really has an bearing on the DSQ or appeal.

[Boomer]

If it were up to me, I would run two like Gill Fuel Flow sensors in line simultaneously and compare the result.

Gill's FIA homologated Fuel Flow meter spec sheet states 52% of meters are within +/_ 0.1% accuracy, and 92% of meters are within +/_ 0.25% accuracy.

so fuel could be flowing at (52% of meters) 99.9 l/hr or 100.1 l/hr difference of 0.2%

or fuel could be flowing at (92% of meters) 99.75 l/hr or 100.25 l/hr difference of 0.5%

Rosberg's race time was 5578.710 seconds, Magnussen's race time was 5605.487, the difference is 0.479% with Ricciardo's time in between. Technically, physically, I think Red Bull have a case.

it is not clear if Red Bull installed their own model of the Gill sensor or something else?

But it looks like they did not follow the FIA reporting procedure, and did not do as they were told to do and use the FIA calibrated sensor, so isn't that is really the issue?

[langwadt]

If it were up to me, I would run two like Gill Fuel Flow sensors in line simultaneously and compare the result.

Gill's FIA homologated Fuel Flow meter spec sheet states 52% of meters are within +/_ 0.1% accuracy, and 92% of meters are within +/_ 0.25% accuracy.

so fuel could be flowing at (52% of meters) 99.9 l/hr or 100.1 l/hr difference of 0.2%

or fuel could be flowing at (92% of meters) 99.75 l/hr or 100.25 l/hr difference of 0.5%

Rosberg's race time was 5578.710 seconds, Magnussen's race time was 5605.487, the difference is 0.479% with Ricciardo's time in between. Technically, physically, I think Red Bull have a case.

it is not clear if Red Bull installed their own model of the Gill sensor or something else?

But it looks like they did not follow the FIA reporting procedure, and did not do as they were told to do and use the FIA calibrated sensor, so isn't that is really the issue?

RB didn't follow there rules that say you have to stay below 100kg/h as measured by the FIA meter

And you'll have to take into account how much of the time they are actually at the flow limit, which to last the race on 100kg can't possibly be more the 2/3 of the time

[DaveW]

In the mean time two other extracts from your reference bother me:

The device shall be able to recover automatically and without action from an incorrect fluid composition (Air bubles for example). I guess they mean "bubbles", that are likely to be found in any agitated fluid system.

I suppose that entrained air bubbles can be thought of as a continuum, ranging from no bubbles to no fluid, and the device would work correctly at one extreme and not at all at the other extreme. The level of entrained bubbles in any circumstance is very likely to be design (hence Team) dependent.

I guess a decision has to be made at what point the device has to register a problem. Does anybody have an idea what flow rate errors are likely to be just before a problem is registered (i.e. will it under-read, or over-read)?

[hardingfv32]

If 'bubbles' were to be used to modify the reading, wouldn't the engine's injectors have to use this 'bubble' fuel supply? Are you thinking that the 'bubbles' can be removed before getting to the engine?

Brian

[DaveW]

If 'bubbles' were to be used to modify the reading, wouldn't the engine's injectors have to use this 'bubble' fuel supply? Are you thinking that the 'bubbles' can be removed before getting to the engine?

I hadn't got that far, Brian. The specification appears to admit that the flow meter will be affected by entrained air. If so, it would be interesting to know if the affected readings would cause the device to over, or under, read.

Actually, I suppose that the device would pass fluid at roughly atmospheric pressure, but the fluid would be compressed before injection, but your guess would be a good as mine.

[Tim.Wright]

maybe I'm showing my igorance about F1 injection systems here but how is this thing plumbed in? I know it's in the fuel tank, but the injection systems I've worked with had a send and receive line to/from the fuel rail. So putting a flow sensor in one of these lines will give you an abnormally high flow rate because most of what is measured is dumped back in the tank.

So to measure the flow rate, you would need to find the difference in flow to the rail compared to back from the rail. But on the Gill sensor there is only one input/output pair.

What gives?

[jz11]

mount the pump with the overflow inside the fuel tank before the flow meter, so all the fuel, that goes through the meter will eventually end up in the engine, if there is a need - put a hydraulic accumulator on your fuel rail to even out pulses, or if you want to - fudge around with the flow meter to get "interesting" readings from it, or have that fuel resonate to your desired frequency and have pressure waves push higher than normal fuel amounts through your injectors - just my theory, but works with the air that goes into N/A IC engines, doesn't it?