Electric propulsion is replacing conventional chemical propulsion in various spacecraft missions owing to their ability to deliver much high specific impulse compared to chemical systems. Amongst various electric thrusters, electric arcjet thrusters have a relatively higher thrust to weight ratio, making them the desired candidate for missions like station keeping. However, they suffer from low efficiency and increased erosion at high power. Therefore, a proper understanding of factors that lead to low efficiency in these thrusters is necessary. A detailed 2D chemical non equilibrium numerical model is developed to simulate the low power arcjet thruster with argon, hydrogen, nitrogen, and simulated hydrazine as a propellant. The numerical model is made up of three solver - plasma flow solver, electromagnetic solver, and anode wall solver. The plasma flow solver contains a mass conservation equation, modified momentum equation, and energy conservation equation to solve the flow inside the thruster. The electromagnetic solver solves the steady-state magnetic induction equation to get the electromagnetic field, and an anode wall solver solves a steady-state heat conduction equation to get the temperature fields in the anode nozzle. The numerical model was validated successfully with the experimental data available in the literature. Identical thruster geometry is used to conduct numerical studies on various propellants. Thruster performance and the energy losses associated with arcjet for various propellants are discussed. Also, the effect of swirl in propellant flow, mass flow rate, radiative heat loss, and composition variation of a mixture of nitrogen and hydrogen propellant on thruster performance are also discussed. Based on the study, the propellant with higher specific heat capacity operated at higher power providing better performance. Higher thermal conductivity resulted in low radiation losses. Exit chemical losses were the main reason for the loss in efficiency for hydrogen and simulated hydrazine operated thrusters. The monoatomic argon operated thrusters showed negligible chemical losses and higher radiation losses