The combustion engines of road vehicles or boats with diesel as well as gasoline have a fairly low efficiency, of the order of 30%. This low efficiency is explained, in part, by the release into the atmosphere of a large amount of heat at the engine exhaust. The temperature at the outlet of the combustion chambers would be of the order of 100 \u00b0 C.<\/p>\n\n\n\n
This\nheat could be exploited via a second engine cycle, the maximum\nefficiency of which would be determined by the ratio of the absolute\ntemperatures (degree Kelvin) corresponding to that at the combustion\noutlet and that of the atmosphere. For example, for a combustion\noutlet temperature of 100 \u00b0 C and an ambient temperature of 10 \u00b0 C,\nthe Carnot efficiency would be 24% representing the maximum\nefficiency attainable by the engine cycle. This efficiency is higher\nfor a lower ambient temperature and lower for a higher ambient\ntemperature (27% at 0 \u00b0 C and 21% at 20 \u00b0 C). However, it appears\nthat significant energy could be extracted from the combustion gases.<\/p>\n\n\n\n
The\nengine cycle would be carried out on the basis of a refrigerant fluid\n(with gas \u2013 liquid phase change) circulating in a closed cycle\nthrough four pieces of equipment or four steps. First, a heat\nexchanger (evaporator) extracts the heat from the combustion gases.\nThe refrigerant carried at high pressure in the exchanger is expanded\nthrough an gas expander (a kind of radial turbine similar to that\nused by turbo expanders of compressed engines) delivering part of the\nenergy contained into the gas. At the end of the expansion, the\nrefrigerant is cooled by ambient air so as to liquefy it through a\nsecond heat exchanger (the condenser). After liquefaction, a pump\nraises the pressure of the liquid to the operating pressure of the\nevaporator. The fluid is then sent to the evaporator to carry out a\nnew cycle.<\/p>\n\n\n\n
This\ncycle is very similar to the heat pump cycle described in the section\non aquathermy except that it works in reverse. The energy supplied by\nthe expander (the enthalpy) is substantially equal to the difference\nin heat taken from the evaporator and released by the condenser.\nThus, the lower the expansion ratio of the expander, the more the\nvalues of heat exchanged by the evaporator and the condenser\nequalized and the lower the energy delivered by the expander and the\nlower the efficiency of the cycle.<\/p>\n\n\n\n
To\nobtain a good cycle efficiency, a refrigerant must be chosen which\nallows the evaporator to operate at high pressure and a short phase\ntransition (from gas to liquid) at the condenser.<\/p>\n\n\n\n
The\nrelease of hot gases into the atmosphere concerns, combustion gases\nfrom motor vehicles (cars, trucks), boats, gas turbines and boilers.\nIt is obvious that is will make more sense when it is applied to\nlarge engines. Applying this technology to small engines of road\nvehicles would require strong efforts in the miniaturisation in order\nnot to penalize these vehicles with limited access.<\/p>\n\n\n\n
This\nmotor cycle mounted at engine exhaust would be fully justified when\nassociated with a carbon dioxide capture feature.<\/p>\n","protected":false},"excerpt":{"rendered":"