fuel pressure control?

[ElectronSpeed]

I have a customer that intends to run his four cylinder in a formula car (i.e. compact battery) with a M800 and no alternator. I am wiring it up for him. Therefore, I am looking for ways to extend his battery life (and simplify things?).

Does anyone have any comments on using the Motec fuel pressure control to reduce the power sent to the fuel pump?

Fuel pump life impact?

Can I get rid of the regulator?

Tricky bits?

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thanks,

Eric Schieb
Electron Speed

[MarkMc]

Hello Eric,
That's quite an interesting question and I am not sure of any investigation into how much power could be saved by doing this.

One thing you would have to take into consideration would be the need for a fuel pump controler, obviously you could not PWM the pump directly from the ECU. The controller could be as simple as a solid state relay with a recirculation diode to protect it.

There should not really be any problems with pump life as long as the pump is always running slightly and you are not trying to stop/start it all the time. Maybe a regulator just to keep the system at least flowwing a little bit of fuel all the time.

[Martin]

On some PDM logging you can also see that the lower you run the fuelpressure, less current is drawn by the pump.

[SportsCarRacer]

Hi, you're idea has some strong merit for the application of reduced battery current draw. I work for an OEM in Powertrain, and have looked in the past at similar means of reducing alternator load, and using the energy more efficiently. Not really justified on OEM scale when piece price cost of more complex components offsets the small gains achieved, but in your specific application, measurable benefit would be quite achievable, on the proviso of several points:
1) Return flow in your fuel system now....OEM's mainly use electronic returnless-fuel systems (ERFS), ie: pump pressure control via speed) as a means of reducing the work done (hence heat added) on the fuel to reduce HC emissions from higher fuel temps. If your pump is sized "just right" (prob not the case with small engine/ bosch pump), your return flow at higher speeds and loads is a small proportion of the total pump flow, thus the energy saved is much less of the total energy to pressureise and moved the volume of fuel.

From this, power used is directly proportional to (mass flow * pressure rise (Pout-Pin))....so, for lower pump power, you have to lower rail pressure or reduce the amount of fuel THE PUMP has to flow. With a reg-bypass type system (and the Poverty version Mechanical returnless system MRFS, with the reg located in the tank, al Mazda/Ford), the volume of fuel flowed is really set by the characteristics of the pump for a given voltage & rail pressure. At lower "engine demand" flows, the balnce of "wasted" vs "engine used" flow changes, low demand = high wastage, pumping up a volume of fuel to rail pressure (heating it!!), then blowing it off to atmos pressure again obver the regulator orifice....the net power wasted = flow rate * (Prail-Patm).....take your return line off the tank during a dyno run, and measuere the amount of returned fuel....all this has consumed wasted elec power!!!! As racers, we tend to FAR oversize the pump syetm to GUARNTEE it will always flow more than what we need, but in turn the pump can be very inefficient pushing over the reg at low flows, and be operating in a VERY inefficent area of the pump curve, and working FAR harder than it needs to!!! In MOST cases, pump pressure control (ERFS) will actually greatly BENEFIT the pump life, albeit with increased complexity.

2) The saving will only be realised with an efficient pump driver device (ie: IGBT, low-on R Mosfet).....ANY resistance in the switching element will cause signifivant losses, as power loss is proportional to current^2*resistance.....we are dealing with relatively high currents. Resistive banks or elements would completely defeat the purpose (ie: element from cooling fan or blower fan controller)....don't laugh, i've seen it done!

3) You would map the engine on the dyno with the return line disconnected and monitor it so a very small amount of return flow is returned...this offers best of both worlds for great trnasient response (the hardest part to get right), but low consumption.

4) Optimise the dwell on the ignition coils...mosy modern pencil COP coils and low-inductance coils can take a fair reduction in dwell (hence current*time=power!!) without a great drop in output......this is a bit harder to optimise, but well worth the effort!!

5) Optimise injector selection....for a given flow range of engien demand, the lowest duty cycle possible can save significant power with 4 injectors running nearly flat out....ie: elec power4x1amp of injectors at 100% duty can be reduced by 40% if you use injectors flowing 40% more for the same duty (60% duty in this case)...subject to having enough low flow to get good idle (same as any BIG injector problem!!)...Peak & hold injectors a bit worse in this regard for time-integral of current (~power used) than saturation (14-16ohm) for the same injector size, due to their turn-on characteristics.

6) Cooling fan optimistion........larger rad, better ducting, etc. to minimise on time of cooling fan...also, run cooling fan PWM to minimise current draw, without big drop in output (once again resistive voltage droppping does nothing, doh!!)

7)Run elec system at highest voltage possible (ie:14.4v instead of 12V)...this reduces the effect of I^2R losses in the distribution cables, but gains are not as big as the above

If it's an FSAE type car, the potential gains are VERY high, as average engine speed is in the lower range of speed/load. If true circuit car, runs at WOT & high speed, gains are still there, but harder to achieve.

Why not go all out, fit small auto alternator onto propshaft, and use Motec to control field current, such that field current is zero whilst throttle depressed (no alernator excitation), but goes to high load excitiation upon throttle closed (overun), utilising the braking energy from regen braking with alternator to assist slowing the vechilce, and charge the batt too!! Truly ingeniuous & efficient, but easy to implement solution, for small weight / rotating inertia penality!

Hope this helps, and i reallly hope you pursue it....racing is losing too many opportunities for novel but simple & effective solutions!

[Allan]

Are there any guides, webinars, sketches on napkins relating to setting up fuel pressure control?

[bing]

Hello Eric,
That's quite an interesting question and I am not sure of any investigation into how much power could be saved by doing this.

One thing you would have to take into consideration would be the need for a fuel pump controler, obviously you could not PWM the pump directly from the ECU. The controller could be as simple as a solid state relay with a recirculation diode to protect it.

There should not really be any problems with pump life as long as the pump is always running slightly and you are not trying to stop/start it all the time. Maybe a regulator just to keep the system at least flowwing a little bit of fuel all the time.

Can you use M DHB to PWM control fuel pump speed?

I have a customer that intends to run his four cylinder in a formula car (i.e. compact battery) with a M800 and no alternator. I am wiring it up for him. Therefore, I am looking for ways to extend his battery life (and simplify things?).

Does anyone have any comments on using the Motec fuel pressure control to reduce the power sent to the fuel pump?

Fuel pump life impact?

Can I get rid of the regulator?

Tricky bits?

.
.
.

thanks,

Eric Schieb
Electron Speed

If M DHB willing to control fuel pump speed/pressure than no return, single line, no regulator is possible.
Of course controlling strategy won't be easy.

Brian.

[ElectronSpeed]

[quote="SportsCarRacer"]
7)Run elec system at highest voltage possible (ie:14.4v instead of 12V)...this reduces the effect of I^2R losses in the distribution cables, but gains are not as big as the above

The battery voltage is lowest during and after starting. If battery voltage rises to a high level, coil dwell, LED headlamp drivers, etc. all adjust to reduce current and the alternator can maintain the voltage. Therefore, we installed a PDM and do a few things like
don't run the fuel tank lift pump until we need it, and
don't run the intercooler pump until we need it.

We also make sure the battery has a good state of charge before the event.

Thanks everyone for the tips. PWMing the fuel pump is still an intriguing option but via (more) careful selection of the pump and the PDM programming have now worked reliably.