Document 65BnoygRGEMZ8L6eb46oL78Km

T able 7. Detailed Requirements for F uel Oils8 HEATING VENTILATING AIR CONDITIONING GUIDE 1942 174 CHAPTER 8. COMBUSTION AND FUELS carbon. In its liquid form oil cannot burn. It must be converted into a gas or vapor by some means. If the excess air is to be kept within efficient limits it means that air must be supplied in carefully regulated quantities. The air and oil vapor must be vigorously mixed to get a rapid and com plete chemical reaction. The better the mixing, the less excess air will be needed. The combustion must take place in a space that maintains the temperatures high so the reaction will not be stopped before CQmpletion. Ififtien equipped with a means of igniting the oil, and safety devices to guard against mishaps, the oil burner becomes efficient and automatic. CLASSIFICATION OF CAS Gas is broadly classified as being either natural or manufactured. Natural gas is a mechanical mixture of several combustible and inert gases rather than a chemical compound. Manufactured gas as dis- Table 8. Approximate Gravity and Calorific Value of Standard Grades of Fuel Oil Commercial N .oStandard 1 2 3 5 6 Approximate Gravitt, Range Baume 38-40 , 34-36 28-32 18-22 14-16 Calorific Value Btu Per Gallon 136,000 138,500 141,000 148,500 152,000 tributed is usually a combination of certain proportions of gases produced by two or more processes. Representative properties of gaseous fuels commonly used in domestic heating are presented in Table 9. Natural gas is the richest of the gases and contains from 80 to 95 per cent methane, with small percentages of the other combustible f hydrocarbons. In addition, it contains from 0.5 to 5.0 per cent of CO2, i and from 1 to 12 or 14 per cent of nitrogen. The heat value varies from | 1000 to 1200 Btu per cubic foot, the majority of natural gases averaging about 1000 Btu per cubic foot. Table 9 shows typical values for the 1 four main oil fields, although values from any one field vary materially. Table 9 also gives the calorific values of the more common types of manufactured gas. Most states have legislation which controls the distri; bution of gas and fixes a minimum limit to its heat content. The gross or higher calorific value usually ranges between 520 and 545 Btu per cubic | foot, with an average of 535. A given heat value may be maintained and yet leave considerable latitude in the composition of the gas so that as distributed the composition is not necessarily the same in different dis tricts, nor at successive times in the same district. However, in any community the variations in gas composition are held within suitable limits so that the performance of approved gas appliances will not be adversely affected. COMBUSTION OF CAS The majority of gas burners utilized in central domestic heating plants are of the Bunsen type and operate with a non-luminous flame. In this 175