Drawing 2.0 A from 9 V battery for 5 seconds
An Estes rocket engine squib looks about like this:



(The above picture comes from a document I wrote on the topic.)

Estes provides very clear all-fire specifications for their squibs:


\$\frac12\:\text{J}\$ within \$50\:\text{ms}\$ into a resistance that is spec'd at \$\frac23\:\Omega\$.


This implies an average of \$\sqrt{\frac{\left[\frac{\frac12\:\text{J}}{50\:\text{ms}}\right]}{\frac23\:\Omega}}\approx 3.9\:\text{A}\$.

As a \$9\:\text{V}\$ alkaline battery will have about 3 times that resistance, internal to the battery. This means that the supply voltage must be \$V \approx 10.4\:\text{V}\$. If you go review the charts at this site, Discharge tests of 9 Volt transistor radio style batteries, I think you'll find that even at just \$1\:\text{A}\$, a fresh \$9\:\text{V}\$ battery might deliver about \$6.5\:\text{V}\$ for a short time. (That chart on that web page is consistent with the figure of about \$2\:\Omega\$ for the internal battery resistance, fresh.) If you were to attempt to draw four times that much, you can be pretty sure that it won't meet the all-fire specification. Not even close.

If you do the calcs, you can perhaps consider adding a \$22\:\text{mF}\$ capacitor with a voltage rating of over \$10\:\text{V}\$, placed in parallel to the \$9\:\text{V}\$ battery. That may work. But they do cost some money and they aren't small.