[Aroy]

Originally Posted by Sutripta

^^^
Hi,
1. Understanding from this and your previous posts, it seems that
a) a 'weaker' spark will result in retarded ignition.
b) the quality of combustion is 'poorer' if started by a 'weak' spark.
Have I understood correctly?

2. Could we have some ballpark figures for designed current.

3. Once again, could we have some quantitative values? In terms of time, from which we can work out the phase angle.

4. I think our understanding of the combustion process has progressed a bit since then! (How did you even find this article!)

5.Nothing really relevant to our discussion here. Essentially some observation on (really) small engines.


6.Talks of a DIY method of checking for a spark. Once again, fail to see the relevance to our discussion.

Regards
Sutripta

1. Yes

2. No idea, will try to get it

3. Will take some time, but the theory is simple - Maximum force of combustion should be just after the piston crosses TDC, so that the piston is pushed in the correct direction. Too early and it will tend to oppose the travel of the piston, too late and the piston will reach the BDC and the force will again be in the wrong direction

4. The great savior of our time - GOOGLE

5. Partially relevant because small single cylinder engines are sensitive to the spark quality. This is the case where any deviation from designed quality will reflect on the starting/running. In a large multicylinder engine the detrimental effects will show up in performance and FE and not necessarily in starting.

6. The idea was to give readers (who are interested) a tip on checking, else it really is OT.

During my college days I experimented a lot with large coils, spark timings and boosted capacitors on my "Jawa". All the points I have given were directly tested and validated in this case. Later on better spark plugs as well as hot/cold combination for city/highway travel was validated on my Fiat 1100. After switching over to MPFI engines I have stopped experimenting, but found that after 1000km of B2B city traffic, a 200+km ride at 100km/h does wonders to FE and performance for the next 1000km of B2B traffic.

[Sutripta]

Originally Posted by Aroy

3. Will take some time, but the theory is simple - Maximum force of combustion should be just after the piston crosses TDC, so that the piston is pushed in the correct direction. Too early and it will tend to oppose the travel of the piston, too late and the piston will reach the BDC and the force will again be in the wrong direction

Was not asking about importance of ignition timing (there is more to it than the simple explanation above), but about quantifying 'weak spark -> retarted timing'

4. The great savior of our time - GOOGLE

You did notice the date of the article?

5. Partially relevant because small single cylinder engines are sensitive to the spark quality. This is the case where any deviation from designed quality will reflect on the starting/running. In a large multicylinder engine the detrimental effects will show up in performance and FE and not necessarily in starting.

Let us leave the starting characteristics of small hand (or kick) started two strokes out for the time being.

6. The idea was to give readers (who are interested) a tip on checking, else it really is OT.

There also used to be available a tong like device in which one could adjust the spark gap and see the spark. Equally irrelevant and OT.

During my college days I experimented a lot with large coils, spark timings and boosted capacitors on my "Jawa". All the points I have given were directly tested and validated in this case.

You actually measured the two points which intrigue me, namely
'weak spark -> retarded ignition timing'
and
'weak spark -> incomplete combustion (but combustion nonetheless)' ?
I mean actually measured and validated. As opposed to 'has to be', 'stands to reason', 'commonsense dictates', 'obviously' etc?

Regards
Sutripta

[SS-Traveller]

Originally Posted by Aroy

A weak spark will have less current, hence may ignite later resulting in both incomplete combustion as well as a retarded timing...

Ajoy-da, I am afraid this statement is something I cannot agree with at all.

Whether the spark is 'weak' or 'strong', if it manages to reach the flash point of the fuel-air charge, combustion/ignition timing cannot change.

It is another matter that a weak spark/grounded spark may not ignite the charge on every cycle.

[Sutripta]

^^^
Thanks SS.
You and I seem to think alike. So I'm sure you've been equally intrigued by some other posts in this thread. Any thoughts?

Regards
Sutripta