You can put a delay on the emitters in the effects themselves, so one follows the next , putting a series of nodes with attach point effects set to a timer should in theory work but coding the thing is going to take some doing , and a fair bit of input from the Good Friar . 

Then you may be in luck as to compose an xml based on a control that uses percentage is not that difficult, like throttle , gear flaps and spoilers.
What was the control in question?

 <PartInfo>
     <Name>show75_85</Name>
         <Visibility>
           <Parameter>
                 <Code>(A:GENERAL ENG THROTTLE LEVER POSITION,percent) 75 &gt; (A:GENERAL ENG THROTTLE LEVER POSITION,percent) 85 &lt; and</Code>
           </Parameter>
              </Visibility>
   </PartInfo>
 
Something along these lines could be used to add visibility at various percentages of throttle and not at others, Dimitri from SamDim used to animate a node and called it a throttle lever (FS9) and had a semi transparent cone that moved in and out  
of the nozzle , you could link an effect to one of these and move the flame , with this whole series on a visibility node above 60 percent or so ... er maybe ...