The Emission of Smoke and Steam. HOW TROUBLE MAY BE AVOIDED.

Progress, Volume I, Issue 7, 1 May 1906, Page 177

The Emission of Smoke and Steam. HOW TROUBLE MAY BE AVOIDED.

In view of the opprobrium to which the owners of steam motor vehicles are liable, it is important that they should make themselves acquainted with the precautions that can be taken to prevent the emission of smoke or of visible vapour. It should be sufficient to show that a vehicle is 50 constructed as to consume its own smoke, but evidence must be given as to the actual construction of the essential 'parts. A short description of the usual devices employed to prevent the creation of smoke, and the emission of visible vapour, will not, therefore, be inappropriate. It must be understood that "to consume its own smoke " is an entirely legal phrase, and is a mechanical and physical impossibility : all that can be done is to prevent the creation of smoke ; once it has been produced it cannot be consumed. A bright red fire will cause no smoke, because all the volatile parts of the coal have been driven off, and nothing but solid carbon is left. As the air passes through the fire bars, the oxygen combines with just so much carbon as is chemically required to create either carbon monoxide or carbon dioxide, both of which are colourless gases. When, however, fresh fuel is necessary, the cold coal is put on the top of the hot fire, and is really " baked " for some little time. During this baking all the volatile hydro-carbons

are driven off as gases. If a stream of air is brought in contact with these gases while they are at a sufficiently high temperature to burn, they will be consumed thoroughly and efficiently. On the other hand, if only a small supply of air reaches these gases they will decompose, the hydrogen combining with the oxygen to form water, and minute particles of solid carbon being freed in the shape of smoke. Oxygen has a much greater affinity for hydrogen than for carbon, and consequently it combines with hydrogen in preference. In order to make the matter quite clear, let it be put this way : if no oxygen reaches the gases which are given off by baking coal, they will leave the chimney as unburnt coal gas — the equivalent of " retorting " an a gas works ; if a very small quantity of oxygen reaches these hot gases, the hydrogen in them will be burnt, whilst the carbon in them will take the form of smoke ; if a sufficient supply of oxygen reaches the gases, they will be entirely and smakelessly burnt. With the conditions ruling in a steamwagon fire box, simple destructive distillation never results, as some unconsumed oxygen is sure to find its way through the lower layers of the fire, and this decompOv.es a little of the gas and causes some smoke. It is, therefore, obvious that some means must be taken to ensure a better supply of air directly smoke becomes visible at the top of the funnel. The usual practice is to open the fire-hole door, and to regulate the admission of extra air by the amount to which this door is opened. When the motor wagon is in motion, the exhaust steam

which discharges through the funnel will draw a much greater supply of air through the fire, so that, by applying the coal in small quantities at short intervals, the air will be found sufficient for combustion ; but directly the engine stops, this induced draught ceases, and it is then that the extra supply of air through the fire-hole door must be given. There is a further provision in the shape of a supplementary steam jet in the funnel, which can be turned on to induce a draught when the engine is not running. The open fire-hole door is a remedy that must only be applied in " homoeopathic " doses ; sufficient air must be admitted to complete combustion, and no more. If too much is admitted, the products of combustion are cooled, so that they cannot communicate much heat to the boiler, and the cold air striking against the tube plates will have a tendency to cause the joints to leak. When to open the door, and when to apply the jet, are questions that circumstances alone can decide ; but, as a general rule, opening the fire-hole door reduces the generation of steam, and turning on the jet increases it. The question of exhaust steam is really quite separate from that of smoke, but a study of the cases that have been brought into the police courts shows that the English policeman is even incapable of distinguishing between black smoke and white exhaust. In some cases where white " visible vapour " has been the sole cause of offence, the policeman has sworn that dense volumes of black smoke were emitted. It will, therefore, be seen that, though the owner may be convinced that the sole cause of complaint had relation to visible vapour he must be prepared to contest it as a smoke cause. A further article will serve, at an early date, to illustrate the devices that are employed to render the exhaust steam invisible, and thus to arm those interested on all these points.

To allow the air to escape from the petrol tank, when the petrol is being added to it, the funnel used should be made with a small air pipe up the side of the stem, which fthe stem) should not be less than an inch in diameter.