Heat is energy, which can flow from higher temperature environment into lower temperature environment. This observation of natural phenomenon is in fact described by second law of thermodynamic as inevitable thermodynamic equilibrium towards maximum entropy, i.e., higher temperature and lower temperature both come to the same. Thermal engines operate between temperature disparity of two isolated system, in which gaseous medium carries heat energy for expansion in engine to do work. After engine extracting energy from the gaseous medium, work is done, and the gaseous medium temperature will drop.
Nicolas Leonard Sadi Carnot, (1 June 1796 – 24 August 1832), postulate that no engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoirs. If to use an equation to define his theorem, it will be like:
In this equation, what is indicated by is that overall energy can be extracted by engine is limited by the ratio of two heat reservoir. The higher of temperature difference, the better engine efficiency.
The reality is quite contradicted with real thermal engines. Our view is purely mechanical design error, not the equation being wrong. Following factors contribute to the lower engine efficiency:
- Turbine is not the right mechanical device to extract energy from two isolated heat reservoirs system. The only high efficiency turbine is hydro turbine because water is incompressible medium. Using turbine to process thermal energy violate Carnot cycle condition as a matter of fact. So we should not expect improve power station efficiency, nor jet engine if turbines are used.
- Only reciprocation piston engine satisfy factor 1.
- When you use solution 2, never use crankshaft because it is worst component to lose energy.
- Better use low heat capacity air as working medium and use water as heat transfer medium.
- Normal air must be compressed without crankshaft.
- Thermal expansion is none linear force, which must be modulated
Carnot theorem efficiency in fact only refers to potential energy of both system that can be utilized by engine to do work in a reversible situation. Nonetheless, it DOESN'T mean heat disparity dictates engine performance efficiency. Quite often, engineers believe that increase high temperature is the way to increase engine efficiency, which is proved to be untrue when you study every thermal engines efficiency.
In this challenge, our goal is to design high power engine working with two heat sources that is no more than 30 degrees Celsius.
This engine will utilize energy from one insulated thermal reservoir, regardless being hotter or colder than the air temperature by 30 degrees Celsius, to work under constant loading until temperature equilibrium reached.
What is the significant value of such challenge? As we know, our living environment temperature changes from day time to night time. Such temperature change, plus other energy sources such as wind, direct day time solar radiation, photovoltaic etc., can firstly store energy as heat and then use engine to either generate electricity or producing hydrogen or methane for long term energy storage. This will solve the problem that renewable energy is intermittent and unreliable. To use hydrogen, carbon dioxide and Sabatier reaction is a better way to reduce emission problem as well.
At such low temperature difference, in order to design high power reciprocation engine, energy flow in the heat exchange system will be under extreme scrutiny for maximum efficiency.