You can look up heat of combustion of the material you are burning this is usually given at a standard temperature (25 C m,15 C. 60 F etc.) Use the heat capacity of the material being burn to calculate the heat required to cool to the standard temperature, calcite heat of combustion at standard condition, heat the combustion products (CO2 + H20) from standard conditions by adding the amount of heat remove to cool to standard Temperature + heat of combustion . You then know the amount of the combustion product (CO2+ H20) ad the temperature either us ideal gas law PV =NRT to find the actual volume flow of the products

As Rick explained, the volumetric flow rate is the mass flow rate divided by the density. You need to know or calculate the temperature. The pressure is likely controlled by the arrangement (equipment). If the temperature is high the products will likely behave as a nearly ideal gas Z=PV/RT, which leaves the average molecular weight of the products and the density is calculated. If the pressure is high (say 40 atm in a gas turbine combustor) you might need to consider a more complicated calculation of density. If you don't know the final temperature or composition, you can always calculate it with CREST. It's free here http://dudleybenton.altervista.org/software/index.html It will also calculate non-deal Z, which you can use to adjust the density.

You can use the NASA Chemical Equlibrium With application (NASA-CEA) online program which can handle any type of reaction. It will give out all the thermodynamic parameters and chemical composition of the product under equibrium reaction. It is very good. I sugeest you try this. Thre link is given below

https://www.grc.nasa.gov/WWW/CEAWeb/