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Disel Injection Timing

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how does Motec ECU know when diesel injection timing is vs when it finishes?

It knows where the engine is in its cycle, and it is controlling the injector?

The ECU knows based on the engine speed what the time taken per revolution is. It also knows at which point in the engine cycle it opens the injector, it knows based on the injector characterisation how long the injector needs to be held open to deliver the correct amount of fuel, and therfore when it will close.

Now in the case of a petrol engine, where you have large pulsewidths, you often need to look at the cycle time (2 engine revolutions on a 4 stroke engine) as the injector is often held open for for than an engine revolution. In diesel applications this is not the case.

For example, on a 4 stroke diesel engine with a 1.1ms pulse-width with a start of injection 12 degrees BTDC at a 2000rpm engine speed:

engine revolutions per sec = 2000rpm / 60 (to change from per minute to per second) = 33.333rev/s

revolution time = 1000 (ms in a sec) / 33 = 30ms per revolution

degrees per millisecond = 12 degrees per millisecond.

We have a 1.1ms pulse. so 1.1*12 = 13.2 degrees of injection.

We started injection fuel at 12 degrees BTDC

So the injection will end 1.2 degrees ATDC

Only a petrol head uses millisecond. Lol we use micro seconds.

(360*enginespeed)/(60*1000)*INJ in microsenconds/1000

Start of injection minus injection angle makes end of injection electrical not real time as there is an opening and close time by the injector but if the fuel flow map is accurate you get correct fuel metering within limits.

With a bit decent data acquisition software your able to make custom channels and you can calculate all of this by using a data log from the ECU. We even go as far as we calculate theoretical power output and compare to real time power calculation based on acceleration and a load more data as well. Interesting what comes out of this from fuel model to real time.