Effect of Cetane Number on Diesel Knock and Injection Calibration

In our region, Euro 4 diesel fuel is available but difficult to find consistently, and most of the time we are using Euro 2 diesel with lower cetane number.

My vehicle is a Toyota Hilux with the 2KD-FTV Euro 4 diesel engine.

Since lower cetane fuel results in longer ignition delay, the combustion behavior is clearly affected (more premixed fuel before ignition and higher tendency for diesel knock).

My question is:

If we want to calibrate or tune the engine to run optimally on low cetane fuel, is advancing SOI (Start of Injection) the correct primary strategy?

And besides SOI adjustment, what other calibration changes should be considered to maintain smooth combustion and avoid knock?

For example:

Rail pressure adjustment

Injection split / pilot strategy changes

Injection timing / rate shaping at higher RPM

Would appreciate insights from anyone experienced with diesel calibration on varying cetane quality fuels.

Farhad,

I'll preface this by saying I do not have direct experience tuning high and low cetane fuel on an experimental platform. My advice is purely theoretical.

Typically when NVH (knock, noise vibration harshness) of the engine is to be reduced, that is achieved via moving SOI closer to TDC, lowering rail pressure, etc.. This advice runs counter to your suggestion. If you advance timing you'll end up injecting more fuel in a cooler chamber further away from TDC and likely exacerbate your problem. The same goes for raising fuel pressure while keeping timing constant, although I might suggest raising fuel pressure under heavy load to counteract the shrinking injection window associated with low timing.

Let us know what you're experiencing and we'll try to help,

Nick