Regarding the research of automotive liquid nitrogen drive system, there are mainly the following aspects.
System circulation research: LN2000 system and CoolN2Car system are the representatives of current liquid nitrogen driving system circulation research. Both are circulation systems that only use liquid nitrogen as the energy storage medium. The working principle is to use liquid nitrogen as the working fluid in the open Rankine cycle, exchange heat in the ambient air heat exchanger, and perform work in the expander.
The main components of the LN2000 system are: low temperature Dewar, cryogenic pump, main heat exchanger, economizer, expander, etc. But the efficiency of the system is only 0.2miles/gallon (about 85km3), and the speed is low, only 22miles/h (about 35.4km/h).
The principle of the LN2000 circulation system is: the liquid nitrogen is sent from the low temperature Dewar to the economizer (preheater) by the cryogenic pump. After being heated by the discharged nitrogen in the economizer, it enters the main heat exchanger, is heated by air, and the pressure rises. High, enter the expander to do work. The exhausted nitrogen returns to the economizer to heat the liquid nitrogen.
LN2000 system and CoolN2Car system are all circulating systems that use liquid nitrogen as the energy storage medium, but they face the following three problems:
①The energy is only provided by the ambient air, and the heat exchange rate is slow;
②The surface of the heat exchanger is easy to be frosted;
③It is highly dependent on the external air environment. Therefore, from a practical point of view, such a system has low power, slow speed, and unstable operation.
Research on the expansion process: The research on the expansion process, theoretically, the specific work* obtained by isothermal expansion is greater. Isothermal expansion is to keep the temperature of the expanding gas constant during the expansion process, but such an expander is difficult to design. The actual isothermal expander has not yet been manufactured. Therefore, there is research on the quasi-isothermal expansion process.
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