Tremendous Heat in Auato. Engines

Sun (Christchurch), Volume VI, Issue 1790, 8 November 1919, Page 11 (Supplement)

Tremendous Heat in Auato. Engines

Few people realise the tremendous quantities of heat which are dealt with in the automobile engine. The heat generated in one hour by an engine developing 25 h.p. is sufficient to raise 3851b of water from the freezing point and turn it into steam (writes an American expert). We do not allow the energy all to go into heat, however, as we want it preserved for mechanical delivery of power at the rear wheels, and consequently we like to carry as little heat as possible away through the jacket and throw it away in the radiator. However, it is impossible to get all of the heat in the engine transferred into mechanical energy. Therefore, we must have some provision for cooling. When everything is normal, the temperature of the cooling water as it leaves the jackets of the engine is somewhere around 180 or 190 degrees Fahrenheit. If it begins to rise above this, or goes above 212 degrees Fahrenheit, which is boiling point, the engine is said to be overheated, and, since the lubricating oil is designed to operate below this temperature, and since the engine

generally is designed to run with a temperature which maintains the cooling water below boiling, it will not perform well above this point. In fact, carbon begins to form, and the performance is generally unsatisfactory. For this reason it is necessary for the owner to maintain his engine in such a way that overheating is avoided. He will be able to do this much more carefully if he knows what provisions are made for cooling his engine, and what are the factors which tend to raise its temperature. Neglecting for the moment the air-cooled engine, and referring to the water-cooled, which is in vast majority, we note that the working portion of the upper part of the cylinder is surrounded by a water jacket. Through this water jacket, by means of a pump or by thermo-syphon circulation, water is continually passing, carrying with it the heat from the cylinder walls, and distributing it to the atmosphere by means of the radiator. The water generally" enters the jacket on one side of the engine, passes through to the

other, and comes up over the top of the cylinder in the head. In some engines the water follows a preconceived passageway; in others it is allowed to circulate freely around the cylinder block. This part of the construction is fixed, and the rate of circulation of the water, by means ofthe pump or thcrmo-syphon, is also fixed and out of the hands of the'driver or car-owner. He can see that they are kept clean by periodically flushing them out with a strong soda solution made up by dissolving a couple of heaped handfuls of soda in a pail of boiling water. He cannot, however, alter the water jackets or change the rate of speed at which the water flows. This is fixed at the factory. Likewise, the size of the radiator and hose connections, etc., are fixed. The fan is a fixed quantity, but the fan belt, by means of which most of the fans are driven, must be kept adjusted properly or the fan will not run at its proper speed. The belt will slip, instead of driving the fan, with the consequence that the required amount of air is not forced through the radiator, and the heat is not carried away. One of the first things to inspect when the engine begins to overheat and the radiator starts to

boil is the fan belt, to see that it is not slipping. Probably the most prolific cause of heat of all is carbon deposit. The piston has a tremendous amount of heat to radiate. It is working in such a location that it cannot come in contact with the water jacket, except through the cylinder walls, and only then at the outside of its diameter. The centre part of the piston or the piston head is exposed to the direct heat of combustion and explosion, and it is natural that it is at this portion that carbon begins to form. The result of carbon forming on the piston head is not clearly understood by scientists even to-day. The theory that the carbon becomes incandescent and causes pre-ignition is beginning to be doubted. While the definite occurrence which takes place is not known, it is certain that a sharp clicking knock, similar to what would be expected from having the' spark too far advanced, does take place. It is found that it is impossible to carry the spark as far ahead when there is carbon in the cylinders, and also that the engine is very prone to overheat because the carbon forms a heat insulation which prevents the heat from being carried out to the water jacket.