About combustion and water ...
By Rémi Guillet (the 03 / 03 / 2012)
The price of fuel and other fuels have not finished "blaze", inducing the recovery of recurring debates (see Wikipedia) as that associated with a certain belief in a mysterious effect more or less a "doping in water "(or other effects resulting from the implementation on engines or other burner of a more or less" opaque system "where the water would suffer" free "energy-transformations, becoming fuel itself!) brings us back to three essential information we think about "combustion and water" information from our thesis " Combustion and wet performance »(Thesis presented in 2002 at the University of Nancy 1 - Henri Poincaré - and directly accessible in full version using the electronic address.
1- Water arriving in an area where combustion is developing (in a thermal machine: internal or external combustion engine, boiler etc. - and whether this water is brought in vapor or liquid form, by the combustion air, by fuel, injected separately -) has every chance of improving the "quality" of combustion (of the fuel identified as such!). Being able to intervene on the atomization of droplets of a liquid fuel (heavy hydrocarbons) as well as on the multiple "intermediate" chemical reactions developed during combustion, this "additional" water allows in certain cases to "difficult" combustions to approach. more (if this is chemically possible), their completeness, thus rejecting less particles and other unburnt materials. In addition, and in all cases, the presence of additional water reduces the formation of NOx, because combustion approaching perfection, especially in the case of stoichiometry, is with this "thermal ballast" additional water comparatively "colder" therefore always less conducive to the formation of nitrogen oxides. (Cf. references indicated in the thesis already mentioned).
2- Thus, the presence of water in the combustion chamber of a thermal machine modifies the physico-chemical dynamics of combustion and if the water supply is controlled, this addition of water, alone, will suffice, via improved combustion, to justify the better performance recorded by said thermal machine: better mechanical efficiency for an engine, or even more "nominal" power, in particular for certain gas turbines ... And greater "ecological discretion"!
From our point of view, there is nothing else to invoke in order to "understand" what is happening with certain engines "doped" by the addition of water. Therefore, starting from an engine “burning” its fuel poorly, therefore necessarily inefficient, the added water has every chance of improving combustion and therefore, concomitantly, of reducing the “consumption” of said engine. Obviously, the more the machine concerned is initially underperforming, the more the benefit linked to the introduction of additional water can be significant! (Cf. the examples often taken on old diesel engines, on two-stroke engines ...)
Conversely, nothing to expect spectacular from an engine in good working order. Note that the quantity of water introduced must always be controlled and not exceed a certain threshold, otherwise it is possible to deviate from the desired effect, other pollution may then appear, in particular with the formation of CO ... (Without forget that water in large quantities suffocates or "extinguishes" the fire!).
3- Now, imagining a thermal machine initially exemplary from the point of view of combustion, it remains that water can allow the thermodynamicist to consider cycles (recovery, regenerative, combined etc.) which can greatly increase the mechanical efficiency of the system (by comparison with the traditional motor, in "open" cycle; see the thesis which largely presents these cycles).
On the other hand, coming back to combustion, another thing to remember. It is about the exploitation of the phase changes of the water resulting from the combustion. Thus its condensation (if it is actually carried out in an ad hoc recuperator) becomes a source of “ultimate” recovery of combustion energy. We are talking about condensing heat generators for “low temperature” heating installations (case of residential heating installations with oversized radiators, with underfloor heating, the temperature of which remains well below 60 ° C, etc.). But one also evokes the cycle * "water vapor pump" which makes it possible to widen the field of application of the said condensing generators in the case of heating at higher temperature, therefore above 60 ° C, that is to say the case of collective heating or other thermal installations in the tertiary sector, etc.). These latest water vapor pumps (or heat exchanger and mass in combustion products before discharge and combustion air) leading de facto to a form of “wet combustion” with its specific ecological virtues guaranteed (in particular that of low NOx, etc.). We can again refer to the often-cited thesis or to the work “From the hygrometric diagram of combustion to water vapor pumps” or to recent articles ** (written in English) appearing on Rémi's author file. Guillet chez l'harmattan under articles contributions like "The water vapor pump cycle underlines the wet combustion advantages"
4 - (Added the 14-10-2015) In the case of reciprocating engines, we can also recall the (formerly well known) “anti-detonating” power of water, an element a priori inert which (if injected in the liquid phase while evaporating, will reduce the end of compression temperature of the mixture), can then lead the thermodynamicist to take advantage of this additional water injection to increase the compression ratio of the cycle and thus improve the mechanical efficiency of the machine, or even its power (matter of balance between the reduction in power energy introduced into the cylinder and the gain in mechanical efficiency of the cycle). (Cf. the reminder in the summary of the title “Wet way combustion” https://www.amenza.ma/wet-way-combustion.html published in 2001 by Elsevier)…
«Additional explanations from the author of the article, Rémi Guillet
1 - The first principle of thermodynamics teaches us that the sum of work + heat exchanged with the exterior of a “system” depends only on the initial state and the final state. Thus the calorific value of a fuel having undergone complete combustion does not depend on the “path followed” (whether there is recycling, intermediate reaction or not!).
2 - With regard to the only production of work (which is the objective sought by a heat engine, it is the "mechanical" parameters of the engine cycle which are decisive (compression ratio in particular, which act on the temperatures in end of compression and end of expansion). Hence the potential interest of additional water which allows an increase in said compression ratio…).
(Reviewed on May 26, 2016) »