Combustion Noise Level

Hi

I have 2 questions about Comustion Plugin to ask as follows

1.What is difference between Knocking and Knocking(transient) and how to determine which one is more suitable in engine testing?

2.How to get more suitable noise threshold in place of defaul value in Knocking and Knocking(transient) setup?

Hi Jim,

The Knocking is the latest knocking algorithm which is much more advanced than the Knocking (transient). We would recommend you to use the new algorithm for better and more precise outputs and results. The main difference is in user inputs and based on the inputs the outputs can be more specific and precise.

Noise threshold is the value that defines the lower limit for the calculation of values. It's defined in Bar.

Best regards
Matjaž

@Matjaž Strniša

Thanks for your reply！but there are some questions to ask as follows

1. I still dont know how to calculate out noise threshold，for example I d like to know why you set 0.05bar as noise threshold in Knocking Transient and seprately set 0.3bar and 0.4bar as noise threshod in Knocking ？why you dont choose other value as default noise threshld.

2.what does mean "decision window" ? in knocking setup. I have learned AVL indicom software, even detection decision window are 20 cycles which is same with dewesoft. I guess Decision window means current cycle pressure should compare with average pressure of 20 cycles before current cycle ,if current cycle pressure "knocing pressure" is larger ,then knocking happened. but this condition need pre-20 cycles does not happen knocking. so I think knocking transient plugin could be more suitable for "dense knocking" engine. is that right?

@Matjaž StrnišaH

Hi，Recntly I take transient knocking plugin to test engine， I found knocing event density is much less than the result of knoing plugin i choose，so i hope you could tell me some details which writened in last question.Any help would be appreciated.

Dear Jim,

I must apologize for such a late reply. I was out of the office due to sickness.

There are two differences between Knocking and Knocking Transient: Filter settings are different and the definition if a cycle is knocking. Knocking is comparing many cycles with each other and defines with this if a cycle is knocking (statistical approach). Knocking transient is deciding if a cycle is knocking within the cycles (comparison of compression with expansion stroke).

Thresholds depend on the engine. Based on experience you can drive in different operating points to the knocking border and calculate the results (knock peak and knock integral or knock ratio). Comparing knocking cycles with non-knocking cycles gives you an idea of which limits are okay.

Threshold values are based on experience and they will not fit each engine. The best approach is to drive a map at the knocking border and compare knocking with non-knocking cycles. Based on your experience you can set possible limits. The difference in your example is depending on the calculation approach. Knocking algorithm has thresholds to block the standard noise of an engine which would be interpreted as knock (absolute adjustment). The threshold in knocking transient gives you an offset for the calculation of the ratio which is more relative (and with this smaller).

The "decision window" is based on the statistical approach of this algorithm. The algorithm estimates that not all cycles are knocking and defines a “minimum base level” of knock peak and knock integral. This base level leads together with the corresponding ratio to the knock limit for the decision. The algorithm never works with mean values. It calculates knock results (knock peak and knock integral) for each cylinder and cycle. Based on this not all 20 cycles aren’t allowed to knock. One non-knocking cycle is enough for the algorithm. But what is correct: The calculation doesn’t work if all cycles (in your case 20) are knocking. This is why knocking transient is available as well (typically used if every cycle is knocking or the operation mode is too dynamic for a statistic). Does dense knocking in your case mean 100% knocking?

About comparing the results between both knocking algorithms, they can be different depending on how many cycles are knocking and the threshold you have chosen.
Please let us know if additional information is needed.

Best regards,
Matjaž

@Matjaž Strniša

Hi Strnisa

Thanks for your so detailed reply and I m so sorry for late reply due to long time bussiness journey.

Dense knocking does not mean 100% knocking, just only very frequent.

I will share your suggestions with my other colleagues, and any question I must tell you.

Warm Regards