Abstract
A rocket engine for space propulsion usually has a nozzle of a large exit area ratio. The nozzle efficiency is greatly affected by the nozzle contour. This paper analysed the effect of the constant capacity ratio in Rao’s method through the design process of an apogee engine. The calculation results show that increasing the heat capacity ratio can produce an expansion contour of smaller expansion angle and exit area ratio. A simple modification of Rao’s method based on thermally perfect gas assumption was made and verified to be more effective. The expansion contour designed by this method has much thinner expansion section and higher performance. For the space engine, a new extension contour type for the end section of the nozzle is proposed. The extension curve bent outward with increasing expansion angle increases the vacuum specific impulse obviously.
Highlights
A de Laval nozzle of large area ratio is generally used in the rocket engines for space propulsion, such as apogee rocket engines that use hypergolic bipropellant combinations
Through a concrete design process of the nozzle of an apogee engine, the methods were verified to be more effective than the traditional method
For a given length of nozzle, the nozzle contour designed with a larger specific heat ratio has a significantly smaller area ratio, and the nozzle performance is almost identical, which is very beneficial to reduce the nozzle weight
Summary
A de Laval nozzle of large area ratio is generally used in the rocket engines for space propulsion, such as apogee rocket engines that use hypergolic bipropellant combinations. S400-15 has the specific impulse of 321 seconds at the nominal point [1], R-4D-14 (HPLAE) has demonstrated a specific impulse of 322:2 ± 2 seconds [2], and the Isv of China’s second-generation 490 N apogee engine is 315 seconds [3, 4]. To improve the specific impulse is still the goal of engine design because the higher specific impulse means a longer life cycle. To achieve this goal, we can increase the combustion efficiency or nozzle efficiency.
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