RURAL ENGINEERING. 291 



classified as 3, 6, and 10 h, p. sizes. With 1 exception 1 engine of each class 

 was obtained from the same manufacturer and each engine was tested under 

 no load, h h i Jind full load. 



The engine details and the test data are given in tabular form. The cost of fuel 

 per brake horsepower was estimated on the basis of gasoline costing 16 cts. 

 per gallon. The length of time for each test depended upon the time required 

 to bring the fuel consumption approximately constant. At no load this occurred 

 in about 90 minutes, at quarter load after 75 minutes, at one-half load after 

 60 minutes, at three-quarter load after 45 minutes, and at maximum load after 15 

 minutes. The fuel consumption became constant before the temperature of 

 the jacket water. 



Curves showing the fuel consumption at various loads for each class indicate 

 that for the 3 and 5 to 7 h. p. engines the economy was greatest at the three- 

 quarter load while for the 8 to 10 h. p. engines it was secured at the maximum 

 loads. Curves showing total fuel, minus that at no load, indicate that up to 

 three-quarter load the friction load of the engine is the chief factor in deter- 

 mining the fuel economy. The 3 and 5 to 7 h. p. classes showed that from 

 three-quarter to maximum load other factors entered which caused a very rapid 

 increase in the fuel consumption per horsepower hour while the 10 h. p. class 

 showed little increase. 



In determining economical sizes for given horsepowers, curves showing the 

 fuel consumption at different loads for different cylinder displacements, which 

 correspond to the 3, 6, and 10 h. p. classes, indicate that from 1.7 to 3 h. p. 

 the engines having a piston displacement of 90.4 cu. ft. per minute were as 

 economical as those having a piston displacement of 55.7 cu. ft. per minute, 

 and that the larger displacement was more economical from 3 to 4 h. p. From 

 4 to 6.75 h. p. the engines having an average displacement of 90.45 cu. ft. per 

 minute were more economical than those having a displacement of 125.4 cu. 

 ft. per minute, but from 6.75 to 10 h. p., the larger displacement was most 

 economical. 



It is concluded that from 1 to 6.75 h. p. the engine having a displacement of 

 90.4 cu. ft. per minute corresponding to a rated 6 h. p. engine is, so far as 

 economy in fuel consumption is concerned, the most desirable engine. For horse- 

 powers above 6.75 the engine having a piston displacement of 125.4 cu. ft. or 

 the 10 h. p. engine, would be the most desirable. 



A new method of cooling gas eng-ines, B. Hopkinson {Gas Engine, 15 

 (1913), No. 10, pp. 568-575, figs. 2; Power, 38 {1913), No. 10, pp. 332-334, fig. 

 l).—lt was found that by injecting cold water in comparatively coarse jets 

 against the internal surface of a gas engine cylinder and the piston head the 

 metal can be kept cool without materially cooling the gases. Other experiments 

 showed that for practical purposes the heat flow into the barrel of the cylinder 

 during the last three-fourths of the expansion stroke was very small compared 

 with that in the first period, so that it was necessary only to direct the spray 

 against the walls in the combustion chamber and the piston, the rest of the 

 cylinder being cooled by conduction. Results of actual tests verify these claims, 

 and it is concluded that the economy is unaffected by the use of this method 

 of cooling since there is no apparent loss in efficiency. 



A traction engine whose four wheels are driving wheels (Engin. and 

 Contract., 40 {1913), No. 1, pp. 112, 113, fig. 1).—A novel traction engine is 

 described which has all 4 wheels the same size and each wheel carrying one- 

 fourth the total weight of the engine. The power plant is a self-balanced 

 2-cylinder, 4-cycle engine. The transmission is through a pinion and large cut 

 gear to a cast-steel gear case under the center of the frame, from which the 



