<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Of course, this approach limits the placement of the sparks. Symmetrically placed sparks would be easy. Asymmetric sparks, for example, two sparks in a 10" long chamber with the sparks located at 2.5" and 5", might be tricky.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">
Not really. Just model it as individual chambers with an imaginary barrier halfway between each spark pair.
Example: If you have a 10-inch chamber with three sparks placed at 3, 5, 7 inches, model it as one chamber four inches long with the spark at 3 inches, one chamber 2 inches long with the spark at 1 inch, and one chamber 4 inches long with the spark at 1 inch.
Using your own example, you'd model it as one virtual chamber of length 3.75", with the spark at 2.5" and a second virtual chamber of length 6.25" with the spark at 1.25".
Of course, the flamefront center and virtual chamber ends will have to move with each timestep. That shouldn't be too difficult, since you're already moving the flamefront center to accomondate the gas expansion due to the breechside flamefront.