420A sequential spark and fuel

[sinisa]

does sequential spark nor injection have positive effect on preventing knock? or it is not worth the trouble

 

[iceguru1114]

For fuel, let's narrow the conversation to port injection. The two modes of electronic injection that I know of are 'sequential' and 'batch' mode injection. Sequential typically fires one injector per cylinder per cycle (4 injection events in total per cycle on a 4-cylinder). When sequential injection is done properly, each injector fires right after the intake valve corresponding to the same cylinder as the injector closes. This uses the heat of the intake valve to help maximize fuel atomization for a more complete and efficient combustion when the air fuel mixture enters the cylinder. It also acts to help cool the intake valve.

Batch mode, on the other hand, fires multiple injectors at once and, therefore, does not make use of the benefits of sequential injection listed above.

For ignition, there's 'wasted spark' and 'sequential'. Wasted spark typically uses whatever ignition advance value was used on the previous compression stroke and fires the plug again at that same crank angle during the exhaust stroke. However, I think there are more advance systems (such as ones from MSD) that can fire mulitple times at various crank angles. However, when it gets that complicated, I personally no longer think of it as a 'wasted' spark system. In my opinion, that's more like an advanced sequential system. I think the argument for wasted spark is twofold: 1) The control logic is easy because you only need a crank signal (no cam necessary). 2) It helps get more unburned fuel out of the cylinder to make room for fresh air on the next cycle. I buy the 1st argument (because it's true), I don't buy the 2nd argument (because correlation doesn't equal causality). On point 2), if you're using wasted spark to help clear the cylinder during blowdown, your mixture was too rich to begin with so wasted spark is a solution to a problem that shouldn't be there in the first place.

Sequential spark, on a 4-stroke engine, usually uses a cam sensor (in addition to a crank sensor) so the ECU can tell the difference between compression and exhaust stroke, and only fire the spark plug once per cycle. The benefit of this is twofold: 1) Less load on ignition components and longer spark plug life. 2) If you have alot of valve overlap, there's less chance of pre-igniting the air fuel mixture during the end of the exhaust stroke/beginning of the intake stroke.

Hope this helps

 

[dsmcrzy]

^ very good explanation. Just to adding to give some personal experience.

When I first installed my megasquirt it was in batch injection and wasted spark. I have since moved to a COP setup going to a fully sequential fuel and spark.

The biggest change I saw/felt was light load/ cruising was a lot smoother than before.