Branching from the Ultimate Diesel thread, can the Fabia vRS adjust it's ignition timing (or equivalent diesely terminology) to produce more power from a higher cetane fuel?

I'd appreciate factual replies rather than opinions here.

Thanks.

Branching from the Ultimate Diesel thread, can the Fabia vRS adjust it's ignition timing (or equivalent diesely terminology) to produce more power from a higher cetane fuel?

I'd appreciate factual replies rather than opinions here.

Thanks.

Hence, the silence has taken you......

Lummox or VRStu may (probably will) know.

J.

nope i dont think so as the diesel only ignites on heat so does not need spark it may adjust the temperature of the glowplugs

im not too sure

There isn't really any "Ignition" as such to be timed as it's all compression based and the glowplugs generally do nothing once running. Timing in a diesel engine is all about when the injection occours.

Cetane is an alkane molecule that ignites very easily under compression, so it was assigned a cetane number of 100. All other hydrocarbons in diesel fuel are indexed to cetane as to how well they ignite under compression. The cetane number therefore measures how quickly the fuel starts to burn (auto-ignites) under diesel engine conditions. Since there are hundreds of components in diesel fuel, with each having a different cetane quality, the overall cetane number of the diesel is the average cetane quality of all the components. There is very little actual cetane in diesel fuel and as mentioned in an earlier thread normal diesel is about 51 and Ultimate is about 55.

A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists auto-ignition and has a longer ignition delay period. How the car works it out if it does at all is unfortunately beyond myself.

To quote the Ross-Tech (Vag-Com) website:

"Note to 1.9 PD (pumpe duse aka unit injectors) owners: You cannot nor do not need to set your timing electronically. There are no graphs published for the simple reason that the timing is set using a dedicated VAG locking tool when changing the timing belt :-)"

HTH.

To quote the Ross-Tech (Vag-Com) website:

"Note to 1.9 PD (pumpe duse aka unit injectors) owners: You cannot nor do not need to set your timing electronically. There are no graphs published for the simple reason that the timing is set using a dedicated VAG locking tool when changing the timing belt :-)"

HTH.

i think that is refering to the valve timing, and the timing of the camshaft driven pump only!

but the answer to the quetion is yes, on the bosch edc15 diesel ecu's it will adjust the timing of the injection cycles to suit the load and rpm of the engine

interestingly, the same ecu is used on many other diesel and turbo diesel engines from other manufacturers also

A fuel with a high cetane number starts to burn shortly after it is injected into the cylinder; it has a short ignition delay period. Conversely, a fuel with a low cetane number resists auto-ignition and has a longer ignition delay period. How the car works it out if it does at all is unfortunately beyond myself.

So does that mean that running a fuel with a higher cetane value could cause the fuel to ignite prematurely and lead to pinking?

I'm not sure how the ECU can adapt to higher cetane fuel - maybe trying various injection timings/durations with the fuel and then trimming the settings, but I would guess that would lead to rough running while it tries?

Chris

So does that mean that running a fuel with a higher cetane value could cause the fuel to ignite prematurely and lead to pinking?

I'm not sure how the ECU can adapt to higher cetane fuel - maybe trying various injection timings/durations with the fuel and then trimming the settings, but I would guess that would lead to rough running while it tries?

Chris

no it wouldn't start pinking, it's not even possible on a diesel engine.

the ecu doesn't adjust anything for fuels with a higher cetane level, the engine just revs up to the same speed more quickly (kind of) it calculates the amount of diesel to to inject based on airflow/rpm/load..... i cant think of a good way of explaining this really!!

So does that mean that running a fuel with a higher cetane value could cause the fuel to ignite prematurely and lead to pinking?

I'm not sure how the ECU can adapt to higher cetane fuel - maybe trying various injection timings/durations with the fuel and then trimming the settings, but I would guess that would lead to rough running while it tries?

Chris

Yeah I suppose it could. I know the theory is sound but there must be some control system in place. From a bit of research I know that the running tolerance of a modern diesel engine is around a rating 46-58. In an older engine it it can cause knocking as these would have to have their timing altered manually but what control system is employed to deal with this I am not sure. I reckon what you have mentioned there has a high amount of merit though

Injection timing is altered by the ECU and there has to be a control system to take into account the air temp/density and a few other things that will make sure the Air/fuel mix ignite at the right time as well as the "burnabillity" of the fuel.

Anyone tech enough on here to help out with this?

is there an echo in here or am i imagineing it??

there is no way of regulating when the fuel will burn, this is solely controlled by the heat created by the compression stroke of the rising piston!

there is no way of regulating when the fuel will burn, this is solely controlled by the heat created by the compression stroke of the rising piston!

So assuming a compression stroke generates heat x, then diesel which will more readily burn can ignite at a lower heat and before the compression stroke is complete? Or have I missed something?

Chris

So assuming a compression stroke generates heat x, then diesel which will more readily burn can ignite at a lower heat and before the compression stroke is complete? Or have I missed something?

Chris

i think it depends a lot on how much cetane you are talking about, in the uk all pump diesel in between about 40-50 iirc?? and there's basically pi$$ all difference between them.... anyway it cant ignite before the end of the compression stroke because the fuel wont have been injected yet. the fuel is injected at the end of the compression stroke, it isn't like a petrol where the fuel is put in on the induction stroke.

is there an echo in here or am i imagineing it??

there is no way of regulating when the fuel will burn, this is solely controlled by the heat created by the compression stroke of the rising piston!

Yes! Heat! Thats it!

Thanks for clearing that up, Tom. Yeah the cetane rating for BS EN590 is 51 min and BP Ultimate claims to be a minimum of 55 so I'm guessing there shouldn't be a whole lot of difference between the two?

Chris