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050 | Staged Injection - MoTeC M1

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One aspect I overlooked mentioning in this webinar was how to calculate what numbers to put in the secondary contribution table if you want to match IDC or in other words achieve the highest fuel delivery possible from your injectors. If your primary and secondary injectors are the same size then a value of 50% will achieve this. If the injectors are different sizes you can use the following calculation:

Secondary Contribution % = Secondary Flow / (Primary Flow + Secondary Flow) * 100

For simplicity this calculation is included in the help file that you can access by pressing F1 in M1 Tune if you are on the secondary contribution table so you don't need to remember it.

Andre can you please explain the reason why injector pw over 7ms at high rpm on a direct port injection motor would damage the injectors. To my understanding during the intake cycle is when the injector fires the cylinder head pressure should be lower than in the other strokes can it be due to possible Valve overlap on these modern engines with variable valve timing? Im just trying to understand why this would damage the injector if the duty cycle at 7500rpm at 7ms is only close to 50%.

This is due to the injector being open during the combustion process, leading to the fuel burning in the injector and creating a carbon build up that can lead to blocked/damaged injectors, as well as excessive heat into the injector.

With DI engines, you want the fuel to be injected on the fill stroke, but not to early that the fuel is injected directly on to the piston crown, (as this causes all sorts of other issues) but you can continue into the compression stroke. All fuel needs to be injected before the spark is fired, and the ECU will change the end point of injection to ensure that the injectors are closed around 10 degrees before the spark event. As the location of the spark event will almost always be changing, then the available pulse width will also be changing. This is why the injection timing is Start of Injection in the DI ECU's, as this allows for the ECU to open the injectors earlier to enable the full fuel delivery to be made.

At 7500 rpm the cycle time is 16 ms however unlike a port injector that can happily inject throughout the entire engine cycle, with a DI injector our window is limited to the intake stroke and part of the compression stroke. This significantly reduces our available injection time when compared to a port injector.

Interestingly BlackRex the stock DI timing map from the factory ECU has SOI @ 375 deg BTDC at high rpm and load (approximately 320 deg BTDC at low load/rpm). This seemed counter intuitive to me as it would be injecting directly onto the top of the piston crown and I too was led to believe that this can be detrimental to piston life. In our FA20 I've seen no ill effect from replicating the OE timing map and if I recall correctly there was an improvement in torque.

I'm unsure if this is a peculiarity of the FA20 piston/DI design and I wouldn't recommend applying that sort of timing across the board to any DI engine. It's always useful if you can view the OE calibration and see what they were doing though as a guide to what could be accepted safe and reliable.

It depends a lot on the location that the injector is in, and it's spray pattern. Compared to port injectors there is a lot of variety in the spray patterns available to suit different designs. With a side mounted injector like the FA20, then there is the possibility that the spray pattern used is a flat fan that sprays across the top of the piston and may interact with the inlet valves when they open as well, without ever touching the piston crown and breaching the boundary layer that protects the piston crown. I haven't pulled a set of injectors out of the FA20 to see what they have as a pattern.

A head with a centrally mounted injector that sprays directly down into the bore onto the top of the piston will have to be treated differently as that can easily be sprayed in a manner that will breach the boundary layer and potentially damage the piston crown.

So this is interesting and brings up a question on the Motec M1 ECU the duty cycle reading is that on a full engine cycle or does it consider that it is DI and calculates based on the injector timing?

Thanks for the info makes more sense now

I was going to write a whole spiel on the calculation of DI Duty Cycle in the M1, but I think that the help probably does it just as well.

TL:DR Essentially the DC on a DI engine being run by an M1 changes based on available injection time, and the Actual Pulse Width at one load site will not relate to the Actual Pulse Width at another load site, even if they have the same DC.

Current fuel injector duty cycle as the ratio of the injection angle related to the maximum available injection angle.

The injection angle is calculated from:

•The maximum of Fuel Cylinder N Primary Output Pulse Width 1

•Engine Speed

The maximum available angle for an injection ensues as the difference between Fuel Timing Primary and Fuel Timing Primary Limit.

If the duty cycle comes near 100% this means the whole span between Fuel Timing Primary and Fuel Timing Primary Limit is needed to deliver the fuel. To avoid truncation of the injection, either Fuel Timing Primary or Fuel Timing Primary Limit can be extended to allow for a longer injection, however this must be done with care to not exceed physical limitations of the engine. Apart from using injectors with a higher flow rate also a higher fuel pressure can shorten the injection itself.

In transient conditions this value can be significantly higher than in constant conditions due to temporary compensation of fuel film effects.

I haven't has an FA20 apart myself but yes BlackRex I'd also assume the injector location/spray pattern avoids the piston crown.

I feel it's always valuable where possible to check the factory calibration as a guide line on what the OE DI timing is doing. I've seen quite a big difference in torque/power based on DI injection timing in the FA20 and basing your timing table off an OE calibration is probably going to get you in the ballpark a lot quicker.

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