Tractor power

The basis of mechanization is the supply of power, in other words, it is the tractor. The actual source of farm power supply is the combustion of a fuel in the tractor engine; the engine produces power which the other tractor components make available at the drawbar, belt pulley and p.t.-o. shaft.

The combustion of a mixture of air and fuel produces heat energy which is converted into mechanical energy by the engine. But considerable heat is inevitably lost with the exhaust gases and to the cooling water and mechanical losses of power occur in friction of the moving parts of the engine, in pumping the air or mixture into the cylinders and the burnt gases out of the cylinders and in driving the engine accessories (such as magneto, fan, etc.). Thus the power actually developed by the engine is very much less than the power equivalent latent in the fuel.

The ignition of a mixture of fuel and air in each cylinder gives rise to high pressure in the combustion space and forces the piston downwards; the piston is connected through a crank arrangement to a crankshaft and the pressure acting on each piston during the power stroke causes a turning effort on the crankshaft. The resultant crankshaft torque multiplied by the speed of crankshaft rotation gives the engine power output.

The major function of the tractor is to provide power at the drawbar for bield work. Power at engine flywheels is transmitted through a change-speed gearbox and various reduction gears to the rear wheels of tracks.

WE spent a considerable amount of time designing and installing measuring instruments. First, there was an electric dynamometre to test the power at the belt under controlled conditions. Thermometres were installed to measure the temperature of cooling water, crankcase oil, and lubricants is the transmission and differential.

Engine speed was checked by means of an electric tachometer indicator. A flashing neon-tube continuously indicated ignition timing. Fuel and air consumption were measured too.

Great care was exercised in the selection of fuels, particularly distillate. The best distillate available was used. It should be pointed out, however, that there is a considerable variation in the quality of distillate throughout the country. The gasoline used for testing was the regular grade and samples were uniform.

Each fuel was put to work under engine conditions best suited to it. For distillate, hot spark plugs, hot manifold, and a cylinder head of 4.32:1 compression ratio were used. For gasoline, cold-type plugs, cold manifold, and a compression ratio of 6.14:1 were used.

Under the same loads and at the same engine speeds gasoline was found to develop slightly over 26 per cent more power than distillate. The fuel saving amounted to approximately 20 per cent by weight.

Under various other conditions the difference between the efficiencies of the two fuels were even more marked.

The program next called for tests in the field.

The site selected for the field tests was Murve Dry Lake on the Mohave desert, in California.

Load was applied by towing another tractor. Additions and modifications in instrumentation had to be made for exact measuring of power at all times under new conditions. In general, the test methods were the same as those used in the laboratory, same engine speeds, compression rations, fuel mixtures, and so on.

After months of work in all kinds of weather we can to the following conclusions: on the average gasoline developed 27 per cent more power at the rear wheel than distillate; gasoline did each unit of work on 21 per cent less fuel, by weight.