Twin spark and Dual Sequential Ignition

Hi. I`d like to know how do Twin spark and i-DSI work?
I know that
- Alfa-engines have 4 valves and 2 plugs (twin spark)
- Mercedes-engines and Porsche-engines have 3 valves and 2 plugs
- new Honda-engines - i-DSI- have 4 valves and 2 plugs (the plugs works sequentially (why not synchronously??)

And i`d like to know how Alfa, Mercedes and Porsche engines works? Sequentially or Synchronously? I think there are many clever guys with technical education here. May someone knows..

P.S. And does everybody know what Honda-motor work synchronously for? What does it give?

Thanks.

How RX-7 car`s engine works?
the plugs works sequentially or synchronously?

Sequential answers all your questions. If two plugs were to fire at the same time, the flame fronts in the combustion chamber would hit each other and put major strain on the engine without a performance gain. In Mercedes's case, one plug fire before TDC and the other fires after TDC. This more completely burns the gas and results in fewer nasty emmisions. A rotary engine fires two different plugs. A leading plug fires at one point in the cycle and a following plug burns the leftover gas later in the cycle. To learn more about rotary engines search www.howstuffworks.com.

But my instutute teacher said that at MB-engine spark happened synchronously. Can you said where do you get your information. Unforunately I cannot understand who says true. My teacher is really good in engines.
Please, answer.

Your teacher may very well be right. Synchro means "at the same time" if you have ever seen sychronized swimming, the swimmers execute the same movements at the same time. Sequence means "one after the other" like walking single file. My understanding of MB ignition is that one plug fires before TDC and another fires after TDC.

Originally posted by DAINTY
But my instutute teacher said that at MB-engine spark happened synchronously. Can you said where do you get your information. Unforunately I cannot understand who says true. My teacher is really good in engines.
Please, answer.

I'm sorry, I can't provide a written source, but here is a thought concept.

Doing dual plugs is expensive, especially to have them fire synchronously. It would be more cost effective for MB to have upped the voltage to the plugs and given a larger gap capability, thus creating the same effect as two plugs firing synchronously, at far less expense.

For power and emission purposes firing sequentially is the only reason to go to the expense of running two plugs per cyl.

At least that's my perspective.