HSIM -- An Open Source Simulator for Amateur Nitrous Hybrid Rocket Motors
Combustion Chamber and Fuel Parameters
| Fuel | In order to simulate a fuel, hsim needs two things. First, it needs a chemical formula. This is used by the cpropep program to simulate combustion. Second, hsim needs to know a fuel regression model. This model describes how the fuel vaporizes and burns as a function of the chamber conditions. Presently hsim has two fuel models, PVC pipe and PBAN. The cpropep models for these fuels are readily available. The fuel regression models come from Todd Moore's HDAS simulator. Other fuels can be added as desired, provided the fuel model data is available. If you'd like another fuel please contact me to discuss. |
| Grain Length | The simulated fuel grain is a cylinder of fuel with a hole, the core, drilled down the middle. This parameter specifies the length of this cylinder. At present this simulator is restricted to this simple model of a fuel grain. |
| Grain Outer Diameter | This parameter specifies the outer diameter of the fuel grain. For many types of amateur-class nitrous hybrids this will be the same as the interior diameter of the flight tank. |
| Grain Initial Core Diameter | This parameter specifies the initial diameter of the hole through the center of the fuel grain. As the fuel burns this diameter increases. Conventional wisdom says that the area of the fuel grain core must be at least 3 times the area of the nozzle throat. Successful engines need not obey this rule; however, this simulator can not be trusted to model such engines. |
| C* Efficiency | This unitless parameter controls an adjustment designed to model incomplete combustion. A value of 1 models complete combustion. Smaller values model incomplete combustion. Until I get an instrumented test stand running I do not know an appropriate value for this parameter. For now I use 0.95 in my simulations. |