MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

149Where electric power is not economically available, large powerrequirements are needed, or mobility is desired, engines can be utilized.As with motors, there are a large variety of sizes and designs; e.g.,air-cooled, water-cooled, two-stroke, four-cylinder, etc. However,the only major difference to be considered here will be among fuels.Engines using gasoline create a mixture of air and gas, ignite them undercompression with an electricspark which causes combustion and thus powerto a driving piston. By modification of such components as the manifold,carburetor, timing, and compression ratio, gasoline engines can be adaptedto burn butane, propane, or natural gas (methane). Engines. for dieselfuel obtain combustion and power by compression along of the fuel andair mixture, which causes ignition. Diesel engines can also be alteredto burn a mixture of diesel and methane (called duel-fuel). Keroseneengines are also commonly used (particularly in developing countries--Molenaar, 1956).The choice of which type engine to use willdepend on availabilityand cost (of both engine and fuel) and power requirements. Table 5.6 listtypical/values and the BHP-hr that can be expected from an engine usingvarious fuels. In general, new gasoline engines have efficiencies of about20 percent, diesel engines slightly higher, and natural gas engines about15-17 percent. Of course, these efficiencies will vary with enginemaintenance and condition.Fuel cost is usually inversely proportional to the price and life ofthe engine with which it can be used. For example, while a typical 10hp gasoline engine might cost about $440 and have a 9 year life, the samesize diesel engine should last about 15 years, but cost about $1,000.(Air-cooled gasoline engines are usually allotted only about a 4 year life.)