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NEWSCIENCENEWSCIENCENEWSCIENCE it contains and thus turn heat into mechani- cal work. This results in the air becoming very cold. The degree of coldness is directly proportional to the applied force and the resistance it encounters. In other words, the heavier the load, the colder the temperature. it contains and thus turn heat into mechani- _ psi through a quarter of its stroke and then __ result that the air supply is cut off. cal work. This results in the air becoming _ the air supply is cut off, and if the piston Having studied the various types of reci- very cold. The degree of coldness is has to do work, it is quite easy to attain _ procating engines, I decided that apart from directly proportional to the applied force — temperatures in the exhaust of minus 50°F. __ trying to follow the third law, certain other and the resistance it encounters. In other This relates to T2 in the temperature dif- _ essential features were necessary: words, the heavier the load, the colder the ference scale, T: being the temperature of 1) Floating valves that can slide on the temperature. the atmosphere—let's say, 70°F. It can reciprocating shaft, towards and away from now be seen that a considerable tempera- each other. This makes it possible to vary THIRD LAW OF THERMODYNAMICS ture difference exists—120°F in this case. _ the length of the stroke, thereby compen- The third law of thermodynamics states This conforms with the second essential — sating for heavy loads. that there are four essential conditions nec- _ condition of the third law. 2) A variable inertia system, enabling essary for a heat engine to work. This Having established the temperature dif- mass to be added or removed from a mov- applies to internal combustion engines such ference, it is now necessary to feed in the ing system. This is used to change the as LP gas, petrol, diesel, steam or com- heat from the atmosphere. As the atmos- _ period of the reciprocating engine. pressed air. These conditions are: pheric air contains the heat (condition 3), if 3) Heat exchanger fins. By adding fins 1) There must be a source of to this type of engine, heat can heat. As an example, with inter- be caused to flow into the nal combustion engines the engine, thus adding to its effi- source of heat is the burning of ciency. fuels such as LP gas or petrol. By applying the above-men- This heat is applied to the com- tioned features, a simple and pressed air in the cylinder at the efficient power conversion sys- moment of ignition. The heat of tem is possible. combustion causes the com- pressed air molecules—already at a pressure, which may be from 150 to 300 psi—to vibrate more intensely, thus increasing the pressure which is applied to the piston face. The heat energy can now be turned into mechani- cal work. 2) There must be a tempera- ture difference in the process. As an example, the temperature CONCLUDING REMARKS Much has been written on the subject of heat engines and their operating principles—so much, in fact, that to the casual reader it would appear that there is lit- tle, if any, part of the subject left untouched. Yet the present-day literature may generally be divided into two classes: the non-technical of combustion may be 700° to and the technical. The technical 900° Fahrenheit (371° to 482° The MKII working prototype of the DLMA Linear Engine. literature is often so severely Celsius) while the temperature technical and theoretical as to of the atmosphere may be 70°F (21°C). obscure the underlying practical aspects. This is represented in thermodynamic _ the engine has heat exchanger fins, and if The student who is not at home with math- terms as T: and T-—here, T: being 700° to they be of suitable size, heat from the ematical gymnastics may well be excused 900°F and T. being 70°F. It can thus be atmosphere will flow into the engine and, _ for being worried at an imposing array of seen that, with such a large temperature _ by doing so, should be turned into mechan- formulae which, however beautiful and difference, a considerable amount of power ical work, thus adding to the efficiency of concise in themselves, possess no interest can be developed. the machine. and serve no useful purpose when they fail 3) There must be a carrier of the heat to convey their significance. energy. This basically means that the airis IMPROVING ENGINE EFFICIENCY It is my hope that the given explanations a medium which carries the heat, just like a Otto was the first to develop the four- make the underlying concepts of thermody- bucket can carry water. stroke cycle and was also one of the first to | namics—on which all heat engines work— 4) There must be a method or means propose using a so-called free piston more understandable and interesting. of turning heat into mechanical work. In engine running on fuel. . . this case it is the familiar piston in the Some years later, in 1869, George For further information, contact: cylinder, examples of which have been Westinghouse patented a steam-driven free Anthony M. Hansen given in the previous essential conditions. piston compressor. _— PO Bea ney Corporation’ Cote nla IMPROVING ENGINE EFFICIENCY Otto was the first to develop the four- stroke cycle and was also one of the first to propose using a so-called free piston engine running on fuel. Some years later, in 1869, George Westinghouse patented a steam-driven free piston compressor. This principle was improved upon by Nikola Tesla in 1894. His design used machined grooves in the piston to let in the steam or air to drive the piston. The main problem with this design is that under a heavy load the stroke will shorten, with the For further information, contact: Anthony M. Hansen Linear Energy Corporation Ltd PO Box 7217 Gold Coast Mail Centre Bundall, Qld 4217, Australia Phone: +61 (0)7 5574 1810 Fax: +61 (0)7 5574 1820 E-mail: linearen@OntheNet.com.au Web: http://www.linearenergy.com.au (See advert on the Inside Cover) THE THIRD LAW APPLIED TO COMPRESSED AIR ENGINES Applying the above conditions of the third law to compressed air engines, if a piston is driven by compressed air at 200 48 - NEXUS The MKII working prototype of the DLMA Linear Engine. FEBRUARY - MARCH 1997