A car engine is just below boiling, and that is COLD? |
Swimming in liquid nitrogenTaking a swim in liquid nitrogen is not a good idea. Don't do this at home, or anywhere else. Liquid nitrogen is over 200° degrees C colder than you are. It wont freeze you instantly, but it will pretty quickly. A car engine at boiling temperature, 100° C, is too hot to touch. The peak air inside a working engine at IDLE, is about 700° C, or 600° degrees C hotter than the engine. At maximum power, peak air temperature is over 1000° degrees, on any scale, Centigrade, Fahrenheit or Kelvin. The engine is over 1000° C colder. For the heated air moving your engine, the temperature of the engine block is so cold, it would be like us swimming in liquid nitrogen, if liquid nitrogen was 4 times colder to us than it already is. That's right, liquid nitrogen would have to be 500 degrees below absolute zero, for it to be as much colder than our bodies, than an engine block is to the heated air that moves your engine. Is there any wonder where the energy went?
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Losing Energy at the speed of soundMolecules hit the sides of the cylinder at the speed of sound. The speed of sound rises with heat and density. So around a thousand times per second each molecule bumps into the cold metal and gives up part of its heat energy. A cylinder "loses" energy in 2 ways, through dissipation of heat, and something called "blow by". Blow by is air leaked by the cylinder rings, and is proportional to pressure times time. Pressure in turn is proportional to temperature. Dissipation is proportional to temperature times time. Years ago, cars with lower compression, like 7 to 1, would idle at 600 rpm or so. Peak pressure from compression is about 14 atmospheres. At 10 to 1, peak pressure is about 25 atmospheres. A single compression/power cycle took 1/10th of a second. How fast is that? You can count to ten out loud as fast as you can in about a second. Today's 10:1 compression cars idle at about 1000 rpm, just under twice as fast. Why? because the peak compression force is about 25 atmospheres, just under twice 14 atmospheres. So it takes just under twice as much energy. But the way compression engine cycles are drawn, you should get all the compression energy back, so why is there energy loss in the system? In the slow part of the engine cycle, heat is leached out from start of compression, through spark and during power stroke. Idle is the speed that energy is added to the system at the same rate it is lost through the radiator, and radiating directly from the engine. If no cooling were done, and insulation added, automobiles would achieve many times the efficiency they have, with the greatest gain at low speeds. Engine temperatures would be up to 1200° C. This is feasible, because Jet engine have internal temperatures up to 2200° C. It would mean huge changes to materials and to engine cost, effectively making car engines cost as much as jet engines. What we grow up with always seems normal. The idea of not cooling an engine goes against life experience. Consider this, one could make the same argument that cooling would extend the life of a steam turbine used to generate electricity. So do you think any electric company cools it's steam off between the boiler and the turbine? No, of course not. That's silly. Cooling a heat engine, water cooling an automobile engine, fails the silliness test. |