Practical Methods of Increasing m.p.g.
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There are Many Ways by Which Petrol is Wasted. Operators Can Save Large Sums by Ensuring that Proper Attention is Paid to All Matters Affecting
THE economic importance of maintaining a high standard of engine efficiency is more generally realized to-day than ever before. Statutory regulations affecting maintenance, and a heavy burden of taxation have made the road transport operator as keen and efficient an executive as any in the commercial world.
Tuning carburetters, testing fuels and recording statistics have become a fine art which warrants the most careful attention if running costs are to be cut to a low level. Checking vehicles to ensure that fuel is not being consumed at a greater rate than necessary is an important duty of the road transport engineer.
Expert tuning, however, constitutes little but a farce unless careful attention be given to other details. The fuel system 8hou1d be examined periodically and all union nuts regularly tightened, because the fact that no leakages are discernible does not necessarily imply that fuel loss by vaporization is not taking place. Undetected waste in this direction may seriously affect m.p.g. figures.
Influence of Driving Methods.
Two identical vehicles with the same carburetter settings, when tested over the same road in the hands of different drivers, can show a surprising dissimilarity in fuel consumption. " Full-throttle" drivers should be checked, as more speed can often be obtained by utilizing half throttle. The driver who is continually surging Iris vehicle instead of maintaining a uniform speed is an expensive employee.
When it is possible to keep drivers on certain vehicles, a petrol bonus system to reward each man on the basis of the m.p.g. attained can be advantageously introduced. The system is made more effective if the spirit of competition be brought into play by publishing the figures weekly. , Maintaining -engine temperatures at night has been a constant problem which up to the present has not been tackled with any great success. The orthodox type of garage heating plant is by no means an effective solution.
Taking into consideration the small capacity of engines in relation to that of the garage, it would appear that the logical approach would be to introduce heat direct to the engine of each vehicle.
Experiments based on this principle led to the introduction of electrical immersion heaters. A recent innovation is a system of direct engine heating known as Radright, marketed by the Carrier-Ross Engineering Co., Ltd. This system has already been installed by several large tmn§port concerns, including Manchester Corporation, and the possibilities of its more extensive adoption appear to be likely.
Steam-heated Cooling Systems.
• The heating medium used in this system is low-pressure steam, generated in a boiler heated by gas, oil, electricity or other fuels capable of being automatically controlled. The steam is introduced into the radiator of each vehicle by means of a flexible tube with a bayonet plug-in cock, the tube to be connected to mains conveniently situated around the garage and fed from the boiler.
A more simple and less expensive method of warming-up engines is the home-made " hay-box, ' which usually consists of old oil drums of 40-50 gallons capacity enclosed in wooden crates and completely packed (including top and bottom) with hay, into which hot water drained from the radiators is poured. A surprisingly small drop in temperature after 12 hours in such a receptacle is evidenced.
This inexpensive system has a further advantage that the tendency to form deposits in the radiators is checked as the water drained from radiators is utilized over and over again, and loses its natural hardness.
High consumption figures are not always the result of mat-adjustment of carburetters. Before attempting to tune a carburetter, m.p.g. figures should be read in conjunction with the mileage covered, class of work, local conditions, mechanical fitness, and weather.
Such factors as recent overhaul, brakes binding, stiffness in the engine and transmission, clutch slip, tyre pressures, and wrongly timed ignition or valves, also have their effect upon petrol consumption, and regular docking, preferably on the mileage basis,is essential if fuel costs are to be kept at a minimum,
Uniform Carburetter Setting.
Carburetter tuning should be in the hands of one man. When vehicle standardization has been adopted it is advisable to maintain one Setting for all vehicles. It is then also possible to hold a spare carburetter suitably tuned which can be fitted when the efficiency of the .original is in doubt. The importance of preventing tampering with jets cannot be over emphasized; it is a particularly reprehensible practice. Jets should be kept sealed, if not, a flow Meter should be utilized and the jets frequently checked for effective size. Such an instrument is an advantage, whether jets be sealed or otherwise, as the orifices tend to become enlarged by constant use.
It is wrong to assume that the smaller the jets the lower the consumption; small jets provide a weak mixture, which may mean that the engine is not developing its full power and so necessitating lower-gear work. Too weak a mixture may also result in burnt exhaust valves.
A function of all carburetters is to atomize a fluid; however, mixing this with a stream of air does not change it into gas. To achieve that •heat is necessary. In the case of the petrol engine this is provided by the engine itself assisted by various devices, notably thermostats.
The use of thermostats and crude
semi-effective radiator blinds all tend to raise the temperature of the air under the bonnet, which is most important, in order to assist vaporization of the liquid fuel.
In this respect the petrol engine and
oil engine differ. In the former the transition of the fuel from a liquid state to a gaseous state is performed before the mixture enters. the combustion chamber, whereas in the compression-ignition engine the actual change takes place in the combustion chamber itself when the atomized fuel contacts with hot compressed air.
Too much heat may detract from economical running, because it may result in the mixture being unduly expanded, with consequent loss of power. Generally speaking, the most beneficial temperature ranges from 100-120 degrees F., and if fine settings are to be used in carburetters it is essential that during winter months cold blasts of air under the bonnet should be prevented and all spaces likely to cause such draughts should be blanked off.
Four Types of Tbersuestat.
There are various types of thermostat ; those incorporated in the cooling system simply prevent weer frame entering the radiator, and so heat it up more quickly. Others open and dose air shutters and so control the cooling draught and interior bonnet temperatures. A third type regulates the heat of the exhaust-jacketed induction pipe, whilst a fourth controts the carburetter itself. This last gives a rich mixture for starting and automatically weakens it when the temperature rises.
When air filters are employed they should be periodically cleaned. Upon initial fitting care should be taken to ensure that they pass sufficient air, as a filter with too small a section of filtering medium will raise consumption by increasing the vacuum on the Jet.
• It has been estimated that more • than 60 per cent, of the carbon removed when an engine is " decoked " is comprised of dust from the air, of which a large proportion is silica, in the form of abrasive particles. There are several efficient types of filter on the market, including the awetted and dry types. Although the former is more expensive to maintain, necessitating periodical applications of oil, its dust-separating efficiency is unsurpassed; both types are cleaned by washing in petrol.
Exhaust-system Efficiency.
'There remains one further component on the vehicle which has a direct bearing on fuel costs and that is the exhausting. system. Back-presstere considerably impairs the efficiency of the engine and increases fuel consumption. It is therefore essential that exhaust systems, whilst effective as silencers, should expel the gases in the most expeditious manner.
The use of inferior and unsuitable fuel results in loss of power and poor consumption figures, together with increased maintenance costs. Improper vaporization is the direct cause of oil dilution, rapid formation of carbon and high cylinder bore wear. The three commonly used additions made to straight petrol are benzole, tetra-ethyl-lead and alcohol. The first makes for more m.p.g., as it contains a greater number of heat units ; it also possesses a high anti-knock propertyTetra-ethyl lead counteracts any tendency towards preignition, whilst alcohol possesses a high anti-knock value, although its calorific value is lower than petrel.
Benzole-bIended spirit has much to recommend it, although it is advisable to adjust the setting of carburetters to cope with a heavier fuel, as a spirit blended with benzoic has a higher specific gravity than a straight petrol mixture. It tends to create slightly more carbon deposit and trouble may be experienced in sooting-up plugs.
At the moment doped petrols are expensive, but the increased and/or more economical production of suitable blending agents may eventually make them an economic proposition. Fuels with octane numbers up to 100 are now in use and the power increase per unit of weight might well attain to 82i per cent., in which event the petrol engine may recover much cf what it has lost to the oil engine, prilvided, of •course, the cost of stick fuel can be reduced to an economic level.
A Snag of Special Fuels..
The greatest disadvantage attached to the use of such fuels is that they require specially designed engines.
The thermal -efficiency ,of the petrol engine may yet, under the spur of necessity, be greatly increased and the gap in the respective fuel economies considerably reduced. Infinitely variable gears and the possibility of being able to devise some means for cutting out unwanted cylinders instead of closing the throttle offer entertaining and profitable lines for research, and we may rest assured that ail such avenues are being carefully explored.