Journal of Thermal and Fluid Science Volume 3, Issue 2, October 2022, pp 38 - 49 https://doi.org/10.26706/jtfs.3.2.20220901 38 Journal of Thermal and Fluid Science https://www.rame.org.in/jtfs/ Preliminary Design of a Ramjet Engine: An Analytical Approach Neeraj Kumar 1* , Vinay Anand Yadav 2 1,2 Department of Aerospace Engineering, Defence Institute of Advanced Technology, Pune 411025, Maharashtra, India neeraj_maero21@diat.ac.in 1 , vinayanand@diat.ac.in 2 * Correspondence: neeraj_maero21@diat.ac.in Abstract: This work is based on preliminary design of Ramjet engine. Ramjet engine is simplest type of gas turbine engine used, which consists of non-moving parts for its operation. It is mainly used for power generation at supersonic speeds. This type of engine is mostly used in missiles, with a few applications in aircrafts. The present approach to preliminary design was based on mathematical equations considering ideal conditions. For the design, aero-thermodynamic equations were used starting with intake and followed by diffuser, combustor and nozzle. For the design purpose, initially Mach 2 and thrust of 10 kN was selected as desired condition. Subsequently, it was analyzed for the varying Mach numbers starting from Mach 1.5 to Mach 4 at desired thrust of 10 kN. Also, the design was analyzed for varying thrust from 6 kN to 22 kN at desired Mach number of 2. The results obtained have been reported and effects of variation of parameters have been represented graphically. The graphs were obtained using GNU Octave 6.4.0. The design achieved could be used for further steps of CAD model generation and subsequent analysis for the required purpose. It can serve as a base for detailed design of the engine. Keywords: Ramjet, aerodynamics, thermodynamics, pressure, temperature 1. Introduction Ramjet engine is simplest type of gas-turbine engine used, which consists of non- moving parts for its operation. It is mainly used for power generation at supersonic speeds. This type of engine is mostly used in missiles, with a few applications in aircrafts. Ramjet engines do not employ rotating turbomachinery to compress inlet air prior to fuel addition and combustion; rather, they compress the incoming air through supersonic inlets and diffusers, where compression is achieved by intricate shock structures in the flow. They are only able to fly at speeds beyond the local speed of sound because they only employ this type of compression. A supersonic combustion ramjet is called scramjet. The lure of ramjets and scramjets is that they offer high Mach number flight, but without the need to carry oxidizer onboard the flight vehicle as in rockets. This results in a higher specific impulse, Isp, which is a general measure of system efficiency. In a typical ramjet engine (shown in Figure 1), supersonic air is ingested by the inlet diffuser and compressed through a series of oblique shocks followed by a normal shock, which, before the airflow reaches the combustor, reduces its speed to subsonic levels. A diverging duct is frequently used to further slow the flow down before it enters the combustor. Fuel is then injected in the combustor where it mixes with the subsonic air and burns to add energy to the airflow [1]. The burned air-fuel mixture is then ejected through a converging-diverging nozzle where it is accelerated to a supersonic velocity out the aft end of the engine (Heiser & Pratt, 1994) [2]. Figure 2 shows a typical ramjet engine designed by NACA [3]. The static thrust of these types of engine are zero, therefore it require assisted take-off for its operation like rocket assist. Article – Peer Reviewed Received: 9 Sept 2022 Accepted: 30 Sept 2022 Published: 7 Oct 2022 Copyright: © 2022 RAME Publishers This is an open access article under the CC BY 4.0 International License. https://creativecommons.org/licens es/by/4.0/ Cite this article: Neeraj Kumar, Vinay Anand Yadav, “Preliminary design of a Ramjet engine: An analytical approach”, Journal of Thermal and Fluid Science, RAME Publishers, vol. 3, issue 2, pp. 38- 49, 2022. https://doi.org/10.26706/jtfs.3.2.20 220901