Optimization research of combustion and energy conversion efficiency of elliptical rotary engine at high altitude using green hydrogen fuel

Hydrogen is a high-energy and sustainable fuel, which can effectively address the combustion deterioration of elliptical rotary engine (ERE) at high altitude. This paper proposes a novel approach by combining zero-dimensional and three-dimensional models to investigate high-altitude performance of hydrogen-blending ERE. Furthermore, the energy loss mechanism between ideal cycle and actual cycle of hydrogen-blending ERE at different hydrogen fractions and altitudes is revealed. The results show that the high-altitude environment leads to a significant increase in post-combustion loss and incomplete combustion loss of ERE using pure jet fuel. The injection of hydrogen with high activation energy can alleviate the combustion delay caused by thin intake at high altitudes. As a result, at 6000 m altitude, 6 % hydrogen fraction can decrease the post-combustion loss and incomplete combustion loss by 10.21 % and 4.63 %, respectively. Therefore, the indicated thermal efficiency is relatively improved by 26.7 %, at an expense of 8.3 % of indicated fuel cost. However, the high temperature caused by the hydrogen combustion intensified the oxidation reaction of nitrogen, resulting in an increase of 1.44 times of NO_x emission. It is worth noting that the thin and low-temperature intake at high altitudes can suppress this phenomenon, and maintain it below 200 ppm.