PRINCIPLES OF FUEL OIL COMBUSTION Combustion is nothing more nor less than a chemical union of oxygen with some combustible material such as carbon. The decaying autumn leaf is an example of combustion. In this case the organic matter of the leaf forms a slow chemical union with the oxygen of The air. Heat accelerates all chemical unions and the greater the intensity of the heat applied, the more rapidly the elements unite. The process of the combustion of the autumn 14af is slow because insufficient heat is developed to induce rapid com bustion.
The explosion of black powder, dynamite or any other of the high explosives, is another example of combustion. Black pow der is a mechanical mixture of sulphur, charcoal and potassium nitrate. In this mixture theoretically each particle of sulphur has beside it one particle of charcoal and one particle of potassium nitrate. Sulphur, which burns easily, is put in the mixture to generate sufficient heat for the liberation of .the oxygen which is contained in the potassium nitrate. Inasmuch as all of the ele ments necessary f or combustion, that is, heat-giving substance, combustible material, and oxygen are combined in black powder. the rate of burning is thousands of times greater than is that of the decaying autumn leaf. Since sulphur, charcoal, and potassiUm nitrate are only mechanically mixed, it follows that in practice every particle of sulphur does not have adjacent to it a particle of charcoal and a particle of potassium nitrate. Accordingly the speed of combustion of black powder is relatively slow as cOni pared with that of the high explosives in which the ing material and the combustible are chemically united so that no matter how finely the explosive may be divided, each atom is com posed of the combustible and of the oxygen-giving material. The heat necessary for the union of combustible and oxygen in the high explosives is generated by an easily explosible, detonator. The intense rapidity of combustion in high explosives is the fact that if a pipe five miles long were filled with nitroglycerine and a blasting cap detonated at one end, the entire column would be converted into gas in about one second.
From these examples it will be seen that the speed and effi ciency of combustion depend upon the intimacy of the mixture of combustible material with oxygen, and that combustion may extend over a long period of time or may be instantaneous. To the engineer, combustion means the chemical union of the com bustible of a fuel and the oxygen of the air at such a rate as to cause rapid increase in temperature.
Fuel oil consists principally of various combinations of hy drogen whose chemical symbol is H, and carbon (C), together with small amounts of nitrogen (N), oxygen (0), sulphur (S). and water The moisture in oil fuel should not exceed two percent because it not only acts as an inert impurity, but must be converted into steam in the furnace, which still further reduces the heat value of the fuel per pound. In the ordinary furnace all the oxygen for the combustion of fuel oil is obtained from the air which is a mechanical mixture of 79.3 parts of nitrogen by volume and 20.7 parts of oxygen.
When the combustible elements of fuel oil unite with oxygen they do so in definite proportions which are always the same Carbon, hydrogen and sulphur require theoretically a certain fixed amount of air for complete burning. The formula for the com plete combustion of carbon is C = One pound of carbon requires for complete combustion 2.66 pounds of oxygen. The dry air requirements for the combustion of one pound of carbon are 11.58 pounds. The formula for the combustion of hydrogen is + = (water). One pound of hy drogen requires for complete combustion 8.00 pounds of oxygen. For the combustion of one pound of hydrogen, 34.8 pounds of dry air are required. The formula for the complete combustion of sulphur is S = One pound of sulphur requires for its complete combustion 1.00 pound of oxygen. For the combus tion of one pound of sulphur, 4.35 pounds of dry air are necessary.