small, high power hybrid
HGDT assumes standard "air" (roughly 1:4 oxygen/nitrogen) as the oxidizer / buffer. There's not really any way to simulate anything other than air/fuel mixes using the fuels provided without heavily modifying the program. With sufficient knowledge of the physical process and how HGDT approximates it you could possibly, with a great deal of effort, decompile HGDT and make something intelligible out of the resulting code, then modify it to suit you. This would very likely be more time consuming than simply writing a new model.
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.