ENGINES AT NIGHT.

New Zealand Herald, Volume LXVI, Issue 20264, 25 May 1929, Page 12 (Supplement)

ENGINES AT NIGHT.

HUMIDITY AND EFFICIENCY.

The idea that cars perform better at night is shared by too many experienced drivers to bo explained by the physical or psychological illusions of darkness. At this season every year it is common to hear drivers in Auckland commenting on the apparent difference in their engines on the morning run to business and on the return after dark. It is vaguely understood that the humidity of the atmospltero is a factor in the performance of an internal combustion engine. Research work was recently carried out in Fngland because differences were noticed , from day to day in the power output from engines operated m laboratories. These variations persisted in spite of allowances for temperature and barometric pressure. It.' was iouud that the discrepancies were due to the variations of humidity of the air in the test room. It is an established fact that, the quantity of water vapour present, in the atmosphere varies considerably from day lo day, and even from hour.to hour. Tests nuide first with absolutely dry air and then with air containing a high percentage of water\ vapour surrounding the engine, showed —in the latter circumstances—a decrease in power of about seven per cent., and it was also found, that when water vapour enters with the air the rate of combustion is slowed, and this, of course, accounts for its influence in preventing " knocking." Owing to this fact an engine working in a humid atmosphero gives the impression of running exceptionally well, not because tho power is greater —it is actually somewhat less—but because all roughness ordinarily duo to detonation disappears under such conditions.

This leads to the interesting deduction that an engino will run more smoothly and will, therefore, appear to bo giving better results than usual, so far as the driver can tell, when the weather is wet or foggy; a dry atmospbero eriables it to give slightly more power, but increases the liability of " knocking." On a thoroughly hot afternoon, following a morning of rain, the atmosphere is heavily charged with moisture; so much so, that nearly fib. of water vapour per hour will enter an engino which is consuming 351b. of air per houiv This means that it will be consuming, say, lib. of water for every 1 i>. of petrol burnt. The same research showed that the cooling system is better off under humid atmospheric conditions, so that boiling is less likely to occur on a wet day even if the atmospheric temperature is high. The petrol consumption is stated (o bo practically independent of (lie degree of humidity, within ordinary limits. Some experts do not agree with the humidity theory although acknowledging improved performance at night. One theory is that an increased proportion of oxygen in the atmosphere at night is responsible. Four years ago an English expert, 1). 11. T. Bond, suggested the following remarkable theory:— " Due to the breathing arrangements of animals and the chemical reactions which take place during combustion, a large quantity of carbon dioxide (CO2) is introduced into the atmosphere, and, unless Nature provided some means of restoring' in an uncombined state the oxygen which goes to form the carbon diox'ide, wo should perish from a lack of oxygen and an excess of carbon dioxide. Nature levels up affairs for us by the way in which she has constructed the organs of all vegetation.. During the day all vegetables absorb or " breathe in " carbon dioxide through their foliage, wher'eupon chemical action ensues internally, and the gas is divided into its two constituents —carbon and oxygen. " The plant now retains, and makes use of, the carbon, and finally exudes the oxygen, in a free and uncombined state at night. It follows, therefore, that, since all vegetation is giving out oxygen at night, there will be a greater percentage present then than during the flay, and, since oxygen is absolutely necessary for combustion—which- is only very fierce oxidation—j.be more oxygen present in the atmosphere the more, perfect will be the combustion of the petrol vapour in the cylinders. The combustion will be more complete and the rate of flame propagation will be higher, from which will follow an increase in efficiency;" TRAFFIC CONGESTION. Traffic congestion, however much it may be discussed, is ill-defined. A City street becomes congested with traffic if vehicular movement is impeded for any cause. ; A country road becomes congested if one slow-moving vehicle . impedes another front overtaking and passing. From these two instances it is seen that what appears to bo congestion of traffic in the thoroughfare) may bo actually a congestion of traffic m the thoroughfare at one point only. Thus an otherwise clear street may be- blocked at intervals, as by signal lights, yet, , properly speaking, there is no. permanent .congestion of traffic as a whole. Similarly batches of live or six cars on a good, wide road will often I7e separated by absolutely clear spaces of half a mile or more. This is not traffic congestion, tholigh the occupants of many cars may believe the roads are crowded; it is merely uneven distribution of traffic. .This bunching of traffic into comparatively small road areas that are overcrowded is easier to explain than to remedy. Nevertheless. it is plain to see that what is usually called congestion of traffic is less a question of area than it is of distribution. EXHAUST-HEATED KETTLE. A picnic kettle which is boiled by heat from the exhaust gases is the latest accessory on the market in England. The kettle and attachments cost less than £2. A permanent adaptor is fitted in the manifold, and (he kettle with its double wall for (he circulation of exhaust gas is clamped on in a few seconds when water is desired. Even small engines furnish sufficient heat lo boil two oi' three pints of water promptly.