Influence of combustion chamber size (L*) on characteristic exhaust velocity (c*) for a N2O/C2H4 premixed green propellant

Abstract

Currently several so called “green propellants” are under investigation to replace the toxic monopropellant hydrazine (N2H4). Aside alternatives as Ammonium dinitramide (ADN)-based propellants, Hydroxylammonium nitrate (HAN)-based mixtures or high concentrated hydrogen peroxide (H2O2), a further promising propellant is a mixture of hydrocarbons with nitrous oxide - called HyNOx or NOFBX. Compared to classical hydrazine N2O/hydrocarbon mixtures offer a high Performance (Isp, c*) a negligible toxicity and low propellant costs. Those substances are also called “premixed monopropellants”: oxidizer and fuel are stored premixed in one tank. To gain experience with a propellant mixture consisting of nitrous oxide (N2O) and ethene (C2H4), DLR is conducting hot gas combustion tests with an experimental combustor. The paper summarizes the results of 134 combustion tests conducted with the premixed propellant injected in gaseous state. Calculated and measured performance (c* and eta c*) depending on mixture ratio, characteristic combustion chamber length (L*) and chamber pressure are shown and discussed. Furthermore the residence time scales of the propellant mixture inside the combustion chamber are normalized by the chemical time scale of the combustion process. Thus combustion efficiencies depending on dimensionless Damköhler numbers are derived.