Lader kommt im kalten Zustand härter wie im warmen! | Posts 16+

It seems like the 'bump' or vibration in my 96kW PD engine is also more noticeable when it's cold.

This could also be related to the fact that, for example, in my engine control unit (ECU), there is a separate injection start map specifically for the "engine cold" condition.
The injection start is regulated to earlier values compared to the warm state, which results in a slightly improved "injection feel," among other things.

Regards,
Ronny.

ronny252 wrote:

This could also be related to the fact that, for example, in my AAT, there is an additional injection start map specifically for the condition "engine cold." There, the start of injection is regulated to earlier values than in the warm state, which results in, among other things, a slightly better "injection quality."

Hi Ronny,

The idea is tempting, but early ignition timing is supposed to only compensate for the longer ignition delay in a cold engine.

The intention is not to increase performance, but it's possible that this could happen if the sensor provides normal readings when the engine is warm, but incorrectly reports lower temperatures, thereby overcompensating for the actual ignition delay.

This can be checked by comparing the water temperature, diesel temperature, and charge air temperature using a VAGCOM diagnostic tool when the engine is cold.

Well, it sounds illogical and crazy, but I only noticed it recently, when we were having almost summery temperatures:

My AGR engine definitely pulls itself out of the low RPM range more easily when it's cold compared to when it's warm.
Although the theory actually suggests otherwise, the engine has more power available from idle speed onwards.

Perhaps the wastegate valves on older turbochargers tend to stick slightly in the end-position range when operating at temperature, preventing them from closing completely. This can lead to a slower pressure build-up and therefore reduced power output at low engine speeds.
It's just a guess.

Ronny252's explanation also sounds reasonable. It might actually be related to the advanced injection timing when the engine is cold, as the EDC compensates for the increased ignition delay. However, it's true that the actual combustion process then proceeds faster, which is very noticeable acoustically through the characteristic "knocking" sound during cold starts.
This could result in improved engine responsiveness, which would be absent when the engine is warm. However, this also increases the peak pressures significantly when the engine is cold, which is why it's best to avoid revving a cold TDI engine excessively.

I can't think of any explanation from the turbocharger side, because a higher exhaust gas temperature would actually be beneficial for increasing the enthalpy difference.
Cold engine oil also tends to impede the turbocharger's spool-up more than warm oil, due to its higher viscous friction.

So, it remains a phenomenon that is not easily explained, or is it?

Regards,
Alex.

The "rumble" settings of the EDC can be easily disabled.

All temperature sensors are given resistors that simulate a fixed temperature (a realistic one).

Then, for the EDC system, the engine would always need to be at the same temperature, and we could only observe real thermal differences in its behavior: thick oil, sticking wastegates, etc.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

donalexo wrote:

It's quite possible that it's actually related to the advanced injection timing when the engine is cold, as the larger ignition delay is compensated for by the EDC. However, it is indeed true that the actual combustion then proceeds faster, which is also very noticeable acoustically due to the knocking during cold start.

Hi Alex,

As far as I understand the process of diesel injection, combustion doesn't start immediately after the injection begins, but with a slight delay.
But once it starts, all the diesel that has been injected up to that point ignites instantly, instead of at a "federal rate."
And this instantaneous combustion creates the cracking sound.

The pressure increase, and therefore the piston force, is not actually higher than normal, but rather increases more rapidly, which quickly compensates for the initial delay.

However, I cannot identify any improved energy efficiency (or effectiveness) that would explain the perceived increase in performance.

Okay, now I've stuck my neck out again as someone who isn't an expert -> Corrections are welcome!

hi,
My Lupo 3L engine actually performs better when it's cold compared to when it's warm.

I can still detect it when the engine is warmed up.

If I let the engine stand for a few minutes until the coolant temperature drops to 60°C, and then start driving, it performs better than when the water temperature is 80°C or 85°C.

greetings

Hi.

@Ulf: That's mostly correct. I just want to add that the fuel during the delay period isn't inert; it already undergoes chemical reactions. The reaction products of these processes burn much more explosively than the injected diesel droplets. This is what gives the knocking sound its metallic quality.

@Dieselmartin: Cold does have an effect. It reduces the amount of work required for compression.

@Powersound3l

'Why does the temperature on your gauge go up to 60°C after a while? Shouldn't it stay constant once the operating temperature is reached, or is that different with the 3L Lupo?'

@Powersound3l

Why does the temperature on your device go up to 60°C after a while? After reaching the operating temperature, it should remain constant, or is this different with the 3L Lupo?

hi,
This is a custom-built device that reads data via OBD, specifically the exact value of the coolant temperature. That's why I don't have a 'plateau' function .
greetings

I meant, of course, when I'm standing still for a few minutes with the engine running.

Oh.

My mistake, I completely forgot that the engine of the 3L Lupo turns off when it's stopped.