液氮发动机的热力循环设计

针对基于单级朗肯循环的液氮发动机效率低和主换热器外表面结霜的问题，设计了基于等熵膨胀的液氮-甲烷-乙烯-R134a四级朗肯循环液氮发动机动力系统新方案.计算结果表明，液氮在所设计的热力循环下的比输出功比采用单级朗肯循环提高了129%；即便充分考虑不可逆因素的影响，液氮的比输出功也远大于蓄电池的比输出功.由于新系统中最上一级热力循环的温度超过水的冰点，避免了主换热器的结霜问题，同时将太阳热能引入新系统，进一步提高了动力系统的效率.比较了基于新循环与基于二级布莱顿循环的液氮动力系统，指出在理想情况下两者的比输出功接近，但当考虑压降和温差等实际因素时，二级布莱顿循环的比输出功远小于所设计的多级多组分朗肯循环.

Thermal cycle design of liquid nitrogen engine

To resolve the frost build-up on the surface of the main heat exchanger and the low efficiency problem encountered in building test bench of liquid nitrogen powered engine,a 4-stage liquid nitrogen-methane-ethylene-R134a isentropic Rankine power cycle was presented.Thermodynamic computation results showed that the specific work output of liquid nitrogen in the new cycle was 129% more than that in the single Rankine cycle.After adequately considering the irreversibility,the energy density of liquid nitrogen was still higher than that of current chemical battery.The new propulsion system can operate in a variety of environmental conditions while not being hampered by the frost build-up,and the solar energy can also be included to extend the vehicle's driving range.Comparison of the presented propulsion system with the system based on Brayton cycle showed that they owned similar specific work output under ideal operation condition,and the isentropic Rankine cycle was better when practical factors like pressure drop and temperature difference were considered.