PRESTDF.XTTAI. ADDKICSS — SKCTION* A. •]•] 



increased ellioicncy, tlio iiiciTasc l)c'ing- greater, lio\\e\(.r. in ihe 

 case of the alcohol fuel than in the case of jietrol. The results 

 of very numerous tests carried out. under the auspices of the 

 United States Bureau of Mines, j^ave no conclusive results as 

 to the eilects of var\in^- jacket tenii)eralure upon the thermal 

 efficiency of internal comhu^tion engines. The direct effects of 

 varying jacket water temperature upon heat losses in the engine 

 are complicated hy such other Aariahles as the luhrication, the 

 fit of the ])iston and \alves, carhurettor adjustment, etc. The 

 improvement in consumption in tests Nos. 5 and 6 over tests 

 Nos. T and 2 may he due to the more perfect comhustion shown, 

 hut it is admitted that high jacket temperatures are very favour- 

 ahle to perfect comlnistion in the case of alcoliol. 



Tests Nos. 7 and 8. — The compression ratio of the engine 

 3.69 is considerably lower than is usual with motor-car engines, 

 especially of British make, and this was increased in these tests 

 to 4.76. The compression space may be reduced bv fa) dis- 

 placing the pistons relatively to tlie cylinders, hy lowering the 

 cylinders on the bed })lates. bv inserting packing ])ieces at the 

 large ends of the connecting rods if they are of the marine type, 

 or by fitting longer connecting rods; or (&) by adding plates 

 to the top of the pistons. The latter method was adopted as 

 the only one i:)0ssible. but the increased weight of metal n:av 

 b^' heat interclianges larp-elv neutralise the increase of thermal 

 efficiency, which ordinarih' accompanies an increase in the com- 

 -^ression ijrc'^surc. .\ sli'^ht improvement was obtained both 

 in the petrol and ale ihol fuel ciinsumi)tion. as ^hown in T:'bl(^ 

 XVT. Tt was impossible to carry th^ eompression ratio fiu"ther 

 owing to the volume of the valve Dockets. In anv case, increase 

 of comnression beyond a certain limit might involve risk, so that 

 to obtain the full a'^nntae'e of hi"-h compression a specially- 

 desis^ned engine would be essential. 



Formation of Deposit ui Cylinders. — At the end of each of 

 the 6 hour runs in tests Nos. 2 and 3, the engine was opened 

 up and carefully examined for deposit formed. yVll deposit was 

 thoroughly removed and analysed. 



The results were as follows : — 



Deposit from Cylinder, Plugs, and Piston Heads. 



]\trol Fuel, Test No. i : 



Weight: 16.15 grams. 

 Ash : 27.06 per cent. 



Alcohol Fuel, Test No. 2: 



Weight : 6.2 grams. 

 Ash : 20.48 per cent. 



The balance in each case was carbonaceous matter. The ash 

 contained ferruginous matter, and included the dust drawn in 



