Chemical reaction (from Supra)

[Greg Hermann]

>If you were to ignite fuel and air (C8H18 + 12.5 O2 >>> 8 CO2 + 9 H20) with
>no addition of heat from the reaction, you would get a 36% increase in
>pressure.  With ignition (assume 1600°F temp increase after combustion,
>PV=nRT, and 80°F init temp) an increase in pressure of 380% from addition of
>heat.  THIS IS JUST BALL PARKISH!!!!!

Not even ballparkish! The (lower) heat of combustion of isooctane is 19065
BTU/lb. Ths temp increase is more like on the order of 4500 degrees.

Greg
>
>The idea Otto cycle is (during combustion) a pressure increase.  Add water
>during this pressure and heat is taken away so less pressure against the
>piston.  Some pressure is gained from the vaporization of water, but I
>"guess" that would not make up for the heat loss/pressure decrease.
>
>See ya,
>
>Mike