Hello
It's understandable that you can "tune" a starter by reconnecting internal connections, cleaning, and lubricating.
It's also clear that the willingness to start decreases rapidly with the starting speed due to increased leakage, lower injection pressure, and increasing compression loss.
However, I still don't understand why the TDI engine often hesitates to start after a warm-up, even though it starts well when cold:
Shouldn't everything be lost in a diesel engine if it doesn't start immediately?
IMO, the optimal ignition conditions should be around the 2nd compression, when the starter has just fully brought the engine to speed. After that, the starting speed should gradually decrease as the starter winding continues to heat up and the battery also starts to fail.
Therefore, the conditions are actually getting worse the longer the engine is "geholt". Nevertheless, the engine usually starts eventually - and I'm wondering:
[b]why bother at all[/b]
Initially, I thought that the accumulation of unburned diesel in the cylinder heads with each unsuccessful injection would increase the compression ratio, allowing the engine to start even with a low RPM.
However, rough calculations suggest otherwise:
A generous estimate of 20 mm³ per stroke would fill the approximately 24 cm³ combustion chamber of a 1.9 engine by 0.08% per injection. Before a truly start-improving compression increase could be achieved (at approximately 4 injections per second and cylinder), the starter and/or battery would likely have given up long ago.
Or should the EDC gradually increase the injection amount during the starting process until the engine eventually starts? Then, it should happen much faster, instead of stressing the driver, battery, and starter for up to 10 seconds or more??
Or does the compression heat only initially dissipate significantly into the surrounding material (as mentioned above), and while the upper layer of material heats up further with each compression, the peak temperature can increase accordingly, effectively "overcompensating" for the declining RPM?
In my tractor, the problem definitely lies in the late injection timing. While the fuel injector is slightly opened during warm-up, interrupting its electrical connection (earliest possible injection start) did not significantly improve the warm-start.
Perhaps I am simply missing something. It would be great if someone could help me . . .
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