Fuel injection timing of Common rail engines 1

[valgaroc]

I know how to adjust fuel injection timings of MC engines.
But, In CR(Common rail engine) I don't know how to adjust it.
The only thing that I know is it is controlled by solenoid valve.

and, It is possible to control fuel injection timing on engine side? Is there any cam shaft or fuel rack in high pressure pump?

 

[BrianPetersen]

The high-pressure pump on a common-rail system does only one thing ... pressurize the fuel in the fuel rail. It has nothing to do with injection timing, it just pressurizes the rail and holds the pressure at a regulated setting.

Injection timing on a common-rail engine is done purely by controlling the timing of the pulses to the injectors, and therefore, the only way to "adjust" it is to change the mapping in the computer. It is otherwise non-adjustable. Same situation as ignition timing in newer gasoline engines with no distributors.

 

[patprimmer]

This is not my area, but logic says it must be timed by an electronic sensor. This may be a crank or cam shaft position sensor. Moving the sensor will change timing, however it is most likely not designed to be adjustable.

Regards
Pat
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[thruthefence]

I'm pretty sure, at least on the Bosch system, the injectors pretty much hose down the intake port/valve all the time. I know the injectors operate by a common ground thru the ECU. The duration of this grounding is determined by the various engine sensors, providing proper fuel metering. As noted, the fuel pressure at the injectors comes from a common fuel rail. A fuel pressure regulator, referenced to manifold pressure, keeps the drop across the injectors pretty much constant at various power settings, by by-passing fuel back to the fuel tank.

 

[ivymike]

had assumed this was a diesel discussion...

 

[thruthefence]

I assumed gasoline. Disregard Bosch ramblings above if diesel.

 

[patprimmer]

Despite the OP failing to disclose details such as ignition type, I presumed diesel as fuel timing was involved.

Regards
Pat
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[dicer]

I guess I'm just slow today. What is an MC engine?
Common rail exsisted, long before electronics controlling engines. The timing was accomplished on a cummins by varing the relationship of the follower to the cam, as the injectors were actuated by cam action similar to the valves. And yes anything newer and controlled by a computer, with either solenoid or piezo injectors, the timing is constantly adjusted by the computer, as it reads information from the various sensors. Its trying to maintain the most power with the best exhaust emissions.
So your outa the loop, unless you can reprogram it like the one guy says.

 

[SomptingGuy]

Mechanical fuel pumps, beautiful though they were, are largely extinct in the automotive world. It's all done with electronics now. A shame really, because the systems they had to control injection timing and quantity (not to mention the governors) were probably more interesting than the engine they were attached to.

There was a cross-over period (e.g. the Lucas EPIC pump). Does any OEM still use unit injectors?

- Steve

 

[BrianPetersen]

Volkswagen "pumpe-duse" unit injector engines are still in production for areas in the world not subject to US EPA Tier 2 or Euro 5 emission standards. But, even in those, they are electronically-controlled unit injectors, and the injection timing is regulated by the solenoid pulse from the computer.

I don't think there are any production automotive or light truck diesel engines that use anything but some variation of common-rail any more, for any place subject to the more stringent emission standards (Tier 2 or Euro 5). They are generally using multiple injections per stroke to control noise and emissions, and they generally have an alternate operating mode with late injection to initiate a regeneration of the particulate filter. It's too hard (I reckon impossible) to do this with anything other than electronic control.

 

[bigpaul]

injector timing on petrol engine overall is altered buy changing the opening (MSPB) Micro second per bit, or injector offset as it is sometimes referded too it, will vary from engine to engine and injector types and makes.
Base fuel pulse width = raw (map) value x microsec/bit(mspb)
Fuel sync is the overall injection start point delay measured in internal units. the numbers can be changed for best emissions or power.

 

[WGJ]

Confusion reigns

Bill

 

[SomptingGuy]

Exactly Bill. Fuel injection has been normal for "real" engines for donkeys' years. It became fashionable for the petrol heads in the eighties, to the point where your car needed an "i" in its tag to be cool. Why they still keep the "i", I'll never know, all cars are.

- Steve

 

[BrianPetersen]

"People not reading" reign.

 

[WGJ]

Reindeers reign.

Cariboo GTi

Bill

 

[tbuelna]

The original poster's question was a valid one. And since he mentioned "fuel rack", it's safe to assume he's talking about a diesel CR high-pressure injection pump.

Controlling rail pressures and flows in a mass-produced 180 bar fuel injection system is actually quite complex. The rail pressures are very high, the flow volumes are very low, the working fluid is incompressible, and the pump output flows must be continuously varied and corrected at a very high frequency rate.

High pressure CR diesel pumps are mostly variable displacement piston pumps. With the displaced volume (per cycle) being controlled by a PW modulated, high-frequency solenoid inlet valve, and a check valve on the discharge side.

Rail pressure control is critical with these very high pressure injection systems, since a small change in relative rail pressures (ie. 26KSI versus 28KSI) can have a huge impact in injector nozzle mass flows. Rail pressures, nozzle orifice diameters and edge geometries, all can have a big impact on fuel mass flows when the injection pressures are 28KSI.

Diesel engines don't require the stringent A/F ratios that a gasoline engine needs. But they still have very sophisticated ECU's and software control laws. A modern piezo-actuated diesel automotive injector is capable of producing up to five separate injection events per cycle, at over 180 bar. Thus each injection event must occur in less than 0.20 milliseconds and is sequential. Pretty impressive.

The typical diesel DI injector control basically has two parameters: Beginning of Injection (BOI) and injection duration (PW). These parameters are controlled by the ECU which uses sensor inputs such as engine temps, air temps, engine speeds, engine loads, manifold pressures, rail pressures, etc., and calculates the correct injector driver values based on mapped software tables, algorithms, and control laws. Some of the more sophisticated ECU's are even capable of modifying these values based on data acquired over the life of the engine.

High pressure CR pumps are basically operating with the same controls as the injectors. The main difference between diesel injection controls and gasoline injection controls, is that gasoline injection systems really require a closed loop type system. Where there is instrumentation feedback from devices like O2 sensors in the exhaust, and air mass flow sensors in the intake, to correct the A/F ratios.

Hope that helps.
Terry

 

[70btdc]

Pat,

Are you suggesting that I can change the start of injection in my common-rail diesel by altering the cam or crank timing signal???? Is this really a sensible suggestion?

 

[patprimmer]

This is not really my area of expertise but I have a general knowledge of EFI systems and diesel engines. To time injection accurately, the computer has to have a reference point. In EFI petrol engines, this is normally supplied by a crank or cam position sensor.

The computer reacts to input from the sensor. Moving the sensor or trigger will tell the computer the crank is in a different position so the injector timing will still be correctly timed relative to the sensor, but at a different crank position. That is if a crank or cam position sensor is used

Regards
Pat
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[BrianPetersen]

Relocating the crank position sensor will of course phase-shift the timing of everything controlled by the ECU (primarily injection timing in an engine like this) by a fixed amount throughout the entire range of RPM and load.

This will probably do something bad ...

One thing that has not been asked: What is the motivation for tinkering with the injection timing? If there is some sort of fault with the engine, perhaps that would be better addressed by fixing the underlying problem rather than attempting to cover it up.

 

[vagman2]

IMHO at least in most modern CR European diesels if you alter the sensor position you'll lose the synchronisation between the crank and cam shafts. That will create faults in the engine's ecu and probably not starting condition.