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Low combustion completeness has been the main defect of hybrid rockets. The present study tries to address the problem by bringing up the setup of the precombustion zone, which do not increase the manufacture cost and complexity.

A precombustion zone can provide a space for the liquid oxidizer to vaporize before entering the combustion zone, and prevents the endothermic effect of liquid oxidizer which can block the chemical reaction as well as the fuel regression. Therefore, this design is expected to raise the combustion completeness. The numerical simulation focuses on the flow field inside a cylindrical hybrid combustor. The distribution of temperature, combustion mode, mass fraction of reactants, velocity, combustion completeness, and solid-fuel regression rate are presented.

With the setup of prevaporized zone of appropriate length, the upstream separation bubble which is unobvious for the case with no prevaporized zone can increase the mixing of reactants, and then increases the combustion completeness. Besides, the radial temperature distribution is more uniform. But when the length of prevaporized zone exceeds about one fourth of the combustor length, due to no enough space for the reactants to react, the combustion completeness begins to decrease and the radial temperature distribution becomes uneven. Therefore, a prevaporized zone with about 24 per cent of the combustor length can have optimum combustion completeness in the present study.

This study provides a useful design to raise the combustion completeness of a traditional hybrid rocket. However, the manufacture cost and complexity are not increased. So the results can be a good reference for the hybrid rocket designers.