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Direct injection tune

Practical Standalone Tuning

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what is the tuning of direct injection in this example?

The car being tuned in this example is direct injection i believe, there is not actually a lot of f difference in how they are tuned,

In this course, Andre himself said that he will ignore the fact that it is direct fuel injection, I would like to know how to tune such direct injection if, for example, he will install larger injectors. Direct Injection has soi and eoi maps and many more that don't have port injection, and I'd like to know how to tune these maps.

Hi Olaf, at this stage we don't have a specific worked example on a DI engine however as Ross mentioned, the tuning predominantly is no different than a PI engine with the exception of sensitivity to injection time and the reduced injection window. There currently is little aftermarket support for DI engines in terms of larger injectors so this really isn't a common tuning change you'll need to deal with (there are some exceptions for example in the VAG world of swapping injectors between engine families). For the most part significant power increases on a DI engine are dealt with by adding a port injection system to compliment the DI. For a better understanding of the DI injector timing and sensitivity to it I'd suggest checking out this webinar: https://www.hpacademy.com/previous-webinars/157-understanding-direct-injector-di-timing/

thanks for the answer, do you have any information about the fuel injection angle?

Hi Olaf,

Direct injection has some very specific requirements, and depending on the ECU strategy (if known can greatly influence the tuning)

In regards to injection timing, you only theoretically have a 360 degree window that fuel can be injected, which is during the intake and compression strokes for the engine.

End of injection considerations:

The effective window is less than that (depending on ECU) as injection taking place after ignition is not recommended. Your 360 degree window has been shortened by up to say 40 degrees now.

Start of injection considerations:

Depending on piston and combustion chamber design, injector spray pattern, injection angle and placement the start of injection can be an important consideration. You are at the end of the exhaust stroke, so the piston is quite hot, as it has been through the combustion process, and pushed the exhaust gases out. The intake air charge is only just beginning to be introduced. The piston also right near the injector nozzle. What can happen when SOI begins too early is that the fuel can breach the gas layer that protects the piston, and gouge and in extreme cases crack the piston.

A less detrimental effect from overly advanced SOI timing is that the fuel has little to no inlet charge to homogenize with, often pooling on cylinder walls causing cylinder wall washing and soot deposits. You also have an increased chance with low speed pre ignition as the cycle time is higher, so the highly atomised fuel has more time to transfer heat.

Generally in the case of reflashing, moving the SOI and EOI limits around too much is ill advised. In the case of fitting a stand alone ECU in place of an OE ECU, good practice is to reverse engineer the injection timing of the OE, and replicate it where possible.

Changing injectors for a DI is a bit of a messy process. For solenoid injectors the inductance of an injector needs to be taken into account due to the voltages and currents involved in driving injectors, as depending on the size of the capacitors inside the ECU that generate the boost voltage, the required charge times may need to be accounted for. Like a port injector, there is an inherent latency of the injector opening before any fuel is delivered. The only issue is measuring the latency and flow rate of an injector is very difficult, as the equipment involved to complete the task is very expensive. Most 'consumer' grade direct injector units can only generate 10 bar of fuel pressure, which means any data is irrelevant to normal operation (40-200 bar in most cases).

For piezo injectors, it is critical that the injector is driven correctly, as incorrectly driving the injector will shatter the piezo crystal.

In both cases, injector spray pattern variances can greatly effect performance, which is why the OE's go to great lengths to ensure injectors can only be installed in one orientation, with locking tabs, locating pins etc.

Regardless, because it requires fairly specialised knowledge, tooling to reverse engineer (a 2 channel scope and amp clamp at a minimum) it isn't really in the scope of the HPA courses. Also if it isn't approached with the correct respect and care, damage to injectors, ECUs or even engines can occur.

Changing injectors and even messing with injection

Very good post, Nathan.

In practice, I'd suggest starting the fuel flow 10-20 degrees before the ignition, I believe (I may be wrong, though) one of the advantages of DI is if the injector is spraying around the spark event there will be a richer fuel density there, so it will be easier to ignite, and that in turn improves the lean burn in the rest of the chamber?

Its a bit of a balancing act, and every engine behaves differently. Also at higher engine speed the cycle time dictates you need to push the SOI closer and closer to the start of the intake stroke.

Having the SOI at 240-350 degrees before tdc allows the fuel a good chance for charge cooling and to mix with the air for even combustion.

If you complete EOI to early pre ignition can become an issue .

Also fuel behaviour changes a bit the further into the compression stroke you get.

Ideally you want to work out the best fuel timing on the dyno where you can accurately measure any gains.

In a lot of turbo applications where you have no secondary injection you find your pushing the timing right out and using almost all of the available injection window, so end of injection is at the exact moment of firing the spark plug, and you start injection earliest safe point.

Sometimes when your on the dyno, and stop to read a plug, you can tell the spray pattern of the injector as it have cleaned the carbon off the piston, as your right on the limit for SOI...

Ah, cool, thanks Nathan. One can always learn - even this old dog.

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