Heat engines able to violate the second law of thermodynamics are COMMONPLACE. This would be obvious if misleading education had not diverted the attention from relevant examples. It is universally taught that all heat engines are NON-ISOTHERMAL, that is, two temperatures, high and low, are ALWAYS NECESSARY:
"In thermodynamics, a heat engine is a system that converts heat or thermal energy - and chemical energy - to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state temperature. A heat "source" generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the "working body" of the engine while transferring heat to the colder "sink" until it reaches a low temperature state." https://en.wikipedia.org/wiki/Heat_engine
"A necessary component of a heat engine, then, is that two temperatures are involved. At one stage the system is heated, at another it is cooled." http://physics.bu.edu/~duffy/py105/Heatengines.html
Not true. There are heat engines functioning in ISOTHERMAL conditions - the two temperatures are not necessary. For instance, the work-producing force can be activated by some chemical agent, not by heating. The analysis of isothermal cycles in which such heat engines produce work shows that the engines are essentially perpetual-motion machines of the second kind.
There is a clear and unambiguous formulation of the second law of thermodynamics given by Sadi Carnot himself:
"A cold body is necessary"
That is, heat cannot be cyclically converted into work unless some temperature gradient is present - a hot body, source of heat, and a cold body, receiver of heat, must be available. The problem is that in 1824 Carnot deduced "A cold body is necessary" from a postulate that eventually turned out to be false:
Carnot's (false) postulate: Heat is an indestructible substance (caloric) that cannot be converted into work by the heat engine.
Unpublished notes written in the period 1824-1832 reveal that, after realizing that his postulate was false, Carnot found "A cold body is necessary" implausible:
Sadi Carnot, REFLECTIONS ON THE MOTIVE POWER OF HEAT, p. 225: "Heat is simply motive power, or rather motion which has changed form. It is a movement among the particles of bodies. Wherever there is destruction of motive power there is, at the same time, production of heat in quantity exactly proportional to the quantity of motive power destroyed. Reciprocally, wherever there is destruction of heat, there is production of motive power." p. 222: "Could a motion (that of radiating heat) produce matter (caloric)? No, undoubtedly; it can only produce a motion. Heat is then the result of a motion. Then it is plain that it could be produced by the consumption of motive power, and that it could produce this power. All the other phenomena - composition and decomposition of bodies, passage to the gaseous state, specific heat, equilibrium of heat, its more or less easy transmission, its constancy in experiments with the calorimeter - could be explained by this hypothesis. But it would be DIFFICULT TO EXPLAIN WHY, IN THE DEVELOPMENT OF MOTIVE POWER BY HEAT, A COLD BODY IS NECESSARY; why, in consuming the heat of a warm body, motion cannot be produced." http://www.nd.edu/~powers/ame.20231/carnot1897.pdf
Generally, a cold body is not necessary, that is, the second law of thermodynamics is false. The cold body is only TECHNOLOGICALLY necessary as it makes heat engines fast-working. Heat engines working under isothermal conditions (in the absence of a cold body) are commonplace but are too slow and impuissant to be of any technological importance. Except, perhaps, for the case where water is placed in an electric field - the non-conservative force (pressure) that emerges between the cathode and the anode, producing cyclical flows in water and able to convert ambient heat into work, seems to be quite vigorous:
Wolfgang K. H. Panofsky, Melba Phillips, Classical Electricity and Magnetism, pp.115-116: "Thus the decrease in force that is experienced between two charges when they are immersed in a dielectric liquid can be understood only by considering the effect of the PRESSURE OF THE LIQUID ON THE CHARGES themselves." http://www.amazon.com/Classical-Electricity-Magnetism-Second-Physics/dp/0486439240?tag=viglink21401-20
"However, in experiments in which a capacitor is submerged in a dielectric liquid the force per unit area exerted by one plate on another is observed to decrease... [...] This apparent paradox can be explained by taking into account the DIFFERENCE IN LIQUID PRESSURE in the field filled space between the plates and the field free region outside the capacitor." http://farside.ph.utexas.edu/teaching/jk1/lectures/node46.html
Tai Chow, Introduction to Electromagnetic Theory: A Modern Perspective, p. 267: "The strictly electric forces between charges on the conductors are not influenced by the presence of the dielectric medium. The medium is polarized, however, and the interaction of the electric field with the polarized medium results in an INCREASED FLUID PRESSURE ON THE CONDUCTORS that reduces the net forces acting on them." http://www.amazon.com/Introduction-To-Electromagnetic-Theory-Perspective/dp/0763738271
Liquid Dielectric Capacitor [Note the turbulent motion between the plates]
"The Formation of the Floating Water Bridge including electric breakdowns"