Extensive research and experiment have been undertaken in recent years with the object of using producer gas in road vehicles, marine craft and stationary units. Ingenious plants are being developed, particularly for heavy road vehicles, on the Continent. Such plants are being used in increasing numbers in countries where liquid fuel is expensive.

  Generally, a vehicle propelled by an internal combustion engine using producer gas costs more to build than a petrol-engined vehicle and less than if it were diesel-engined, but the fuel cost is considerably lower than for steam, petrol or diesel. The entire plant is mounted on the vehicle and the engine, instead of being supplied with liquid fuel, is fed with gas derived from solid fuel such as charcoal, coke or anthracite, and generated on the vehicle itself. After the gas has been cleaned it is fed to an internal combustion engine. Although petrol engines have been run on producer gas, the practice is either to alter an engine to suit the properties of the gas or to install an engine which is initially designed for producer gas.

  For the sake of convenience or to ensure instant starting and to avoid waiting for gas to be generated, a small supply of petrol is generally carried and a carburettor is fitted to the engine. Although the petrol is not essential, this provision makes for adaptability of the vehicle. The engine will not operate with equal efficiency on either fuel, but the provision for both is a safeguard, especially in remote countries where the vehicles may have to be used in districts where one fuel is not to be obtained. Producer gas affords an alternative to oil fuel, and the gas is suitable for firing furnaces, for heating and for various purposes in addition to road transport. There are limitations to its use where space and weight are of paramount importance, as in aircraft or in small motor cars, and it lags behind liquid fuel for convenience and for power-to-weight ratio. Such great improvements have been made, however, that the producer gas engine enables heavy road vehicles in countries lacking oil wells to be run independently of imported oil on home-produced fuel at a fraction of the fuel costs.

PRODUCER-GAS PLANT can be fitted to an ordinary internal combustion engine, or else a specially designed engine can be installed on the chassis. The car illustrated is fitted with a Koela plant, and in an R.A.C. rally in 1934 this car completed 1,000 miles on 660 lb. of charcoal and six gallons of petrol. The petrol was used for various tests. Solid fuel is emptied, as shown, into a hopper above the firebox of the producer.

  Coal gas carried in containers was used to drive cars and lorries during the war of 1914-18, and since then vehicles have been driven by gas stored in high-pressure cylinders. The producer gas vehicle is a miniature gasworks on wheels. The heat generated by the fire has to be localized and noxious fumes must be avoided The gas must be sufficient to give a considerable mileage, thus overcoming the drawback - suffered by users of compressed gas - of restriction to the vicinity of gas-compressing stations.

  There are various types of producer in use. The equipment manufactured in Great Britain by the Koela Producer-Gas Plant Company, Ltd., is based on principles arrived at by research into every aspect of the problem, the subjects ranging from special heat-resisting steels to the coking qualities of various coals. The company has concentrated on two main lines of development - first, the conversion of existing chassis or engines, a process involving alteration to the cylinder heads according to Koela patents ; secondly, the fitting of engines to new chassis.

  After extensive experiments with various fuels, including wood, anthracite, heavy oil and gas coke, the company concentrated upon two fuels, charcoal and low-temperature coke. If difficulty is experienced in obtaining charcoal, kilns of various sizes are supplied. The equipment is composed of three elements. The first of these comprises the generator, the preheater and the fuel hopper, and its function is to convert fuel into combustible gas. The second element comprises the expansion box and cleaners, where the gas is cooled and hot or condensable impurities are removed Expansion box and cleaners also act as gas reservoirs. The third element is a final filter where the remaining impurities are removed after the gas has been mixed with the secondary air necessary to form an explosive mixture.

Five Standard Plants

  Dimensions of the units vary according to the horse-power and cubic capacity of the engine, and can be altered, except for certain basic measurements, to suit requirements. Five standard plants are made to suit engines ranging from 35 to 165 horse-power. The units are designed to provide a simple, sturdy generator with adequate cleaners and filters, so that operation and upkeep are straightforward.

  The producer is generally installed on the running board of a lorry, in front of the door of the driver's cab, and the second and third elements of the equipment are mounted on the running board or on brackets on either side of the chassis. The gas passes from the producer to the first cleaner, mounted behind it on the same side of the lorry, then passes across the chassis to the final filter, from which it passes to the engine induction manifold. By the placing of the producer on the side opposite the induction manifold, the flexible piping is reduced to a minimum, as the gas flows first across the chassis and then forwards to the engine.

  The fuel is placed in a cylindrical hopper above the firebox of the producer (see sketch, below). The hopper generally contains sufficient fuel for about fifty miles. The firebox has a lining of refractory material, and the grate is made of heat-resisting non-corrosive steel. A small water tank and drip feed supply the vertical vaporizer and preheater, bolted to the side of the casing. At the top of the preheater is a blower operated by turning a handle. This blower is mounted at the head of the air inlet pipe to create a forced draught.

THE FINAL FILTER, the last of the three elements of the Koela producer-gas plant, is generally placed on the side of the chassis opposite to the producer itself. The gas passes from the producer, through the expansion chamber and cleaners, then across the chassis to the final filter, which is placed opposite the engine induction manifold. In the final filter any remaining impurities are removed from the explosive mixture of gas and air before it enters the cylinders.

  The fire is lighted in the base of the producer with paper and wood, the furnace door is closed and the lower section of the producer is filled with fuel. The blower is brought into action by turning the handle, and when the fire is glowing the fuel is fed into the hopper, filling it, and the lid is clamped down.

  After a period of from six to twelve minutes the engine can be started on gas, and operation is the same as with a petrol engine. Provided that the fuel level is not allowed to fall below the level of the top of the cone in the hopper, a fact that will be indicated by the normally cool hopper becoming warm, the fuel may be replenished without stopping the engine.

  Air is drawn into the producer through the air inlet pipe by engine suction. As the air passes on its way to the producer through the preheater, water is added by the controllable drip feed at from two to four drops a second. In the preheater the incoming water is heated and vaporized by the hot gas from the producer. On entering the base of the producer the air and steam are distributed through apertures in a ring, giving even combustion over the whole grate. As the mixture passes through the fuel bed, carbon dioxide is formed and the steam is "cracked" into its constituent gases. Before reaching the top of the fuel bed, the gases are further reduced and combined, producing a combustible gas.

  This is collected again by the ring to ensure even combustion and passes down the casing of the preheater, which it heats. It passes on through a pipe to the second element, the expansion box and cleaners, where it is cleaned as it passes through coconut matting trays and wood-wool or wire-wool, controlled by a series of baffles. The design enables these to be cleaned easily and provides ready access. The cleaner is a welded box, with gastight doors to enable dust to be removed. The gas passes to the third element, the final filter, where non-condensable impurities are removed by interaction with oil mist. Cleaners and filters eliminate the risk of damage to the engine, and the low resistance to the flow of the gas offered by all three elements prevents loss of power.

From Haifa to Kabul

  The gas passes from the filtel to a special induction pipe connected to the engine induction manifold. On this pipe are an air inlet valve and a gas throttle, controlled by the driver. The petrol carburettor can be retained, if desired, but petrol is for use only in special circumstances.

  The engine should have a compression ratio of 6.5 to 1, and in some instances this can be achieved by machining the head of an existing engine. Koela patented cylinder heads are designed to operate on gas, turbulence and scavenging being improved. In circumstances where the valve arrangement does not permit cylinder head alterations, special pistons provide a further alternative. The difference in power between an engine altered to operate on producer gas and a normal engine running on petrol has been reduced to not more than 10 per cent, the petrol giving the higher power. When an equal power output is required an engine built to operate on producer gas is supplied.

  If necessary the gas can be tested before the engine is started. To do this the air valve on the engine is opened and gas is forced from it by operating the blower. The gas is ignited and the quality shown by the steadiness of the flame. To start from cold on gas the air valve is set, the gas throttle opened and the engine turned by the electric starter. Alternatively, the engine may be started on petrol and changed over to gas by opening the air valve and gas throttle and then shutting off the petrol.

ARRANGEMENT OF PRODUCER-GAS PLANT as designed by Gilfords (H.S.G.), Ltd., for road vehicles. The producer is an unlined mild-steel cylinder about 2 feet high, filled with fuel from the top. A water-cooled tube known as a tuyere (left) admits air into the fuel at high velocities. Water passed into the fire from a drip feed forms an aqueous envelope round the fire zone. The gas produced first passes to the expansion chamber, a cylinder fitted with baffles, and then through the cleaners, where compressed sisal extracts carbon and other impurities. The gas then passes through the final cleaner to the engine.

  The fuels and the design have been studied to provide lightness and compactness throughout. Ashes are removed from the ashpit at the end of the day's run by means of a door. With clean fuel there is no tendency to clinker, and the producer needs cleaning only at the end of the week.

As evidence of the reliability of this type of producer there are lorries, agricultural tractors, buses and small vessels operating successfully in India. Burma, China, Rhodesia, Syria, Latvia, Russia and elsewhere. In 1933 two 1-ton vans made a journey from Haifa through Damascus, Baghdad and Tehran to Kabul, the capital of Afghanistan ; they used gas generated from charcoal bought on the route.

  The journey involved the crossing of the Syrian Desert and the climbing of mountain roads to an altitude of 8,000 feet in Afghanistan.

  In the R.A.C. Bournemouth Rally of 1934 a motor car, with engine unaltered, was fitted with a producer-gas plant. The vehicle completed 1,000 miles on 660 lb. of charcoal and six gallons of petrol, the petrol being required for certain tests. The reduction in fuel costs varies according to the price of petrol and in general represents a saving of from 60 to 90 per cent.

  Another producer-gas plant is that of Gilfords (H.S.G-.) Ltd., whose "High Speed Gas" process differs considerably from the usual practice of generating gas with the aid of preheated steam. The object of this patent method is to accelerate gas making. To achieve this the design of the producer is different, and water, not steam, is used.

  The producer does not need a refractory lining. The space allocated to the making of gas for an engine of 100 horse-power is so reduced and the insulation of the flame by an envelope of water vapour is so effective that an unlined cylinder of 12-gauge mild steel, 2 feet in diameter and 2 feet high, is a sufficient firebox. The geneiator has a door at the top to enable it to be filled with fuel, with an internal baffle above the combustion area to prevent the fuel from packing tightly when subjected to road shocks. At the bottom is the clinker discharge outlet. A water-cooled tuyere (tube) is mounted to project into the firebox, and the gas outlet is mounted on the opposite side at a slightly higher level.

The fire is built up of concentric zones by admitting the air into the fuel bed through the tuyere at high velocities. The temperature of the carbon dioxide zone, which is the hottest zone, where the air, as yet in excess, meets the burning carbon, is higher than usual. The space and time for the conversion of a given weight of fuel into gas are therefore contracted. The tendency of the fire to spread is checked by enveloping it in an aqueous envelope, which is produced by using water instead of steam.

  Suction is applied at the gas outlet, a flame is held near the inlet and a fire is established, producing carbon monoxide. When the water drip is turned on hydrogen appears and the plant is at work.

  The air rushing in through the tuyere tends to form a small zone of no combustion at the tip of the nozzle, and we will call this Zone A. In Zone B, however, where the carbon dioxide is formed at an almost instantaneous speed, the temperature is at its highest and has been measured by optical pyrometer. The temperature so measured was 1,500 degrees centigrade. In Zone C, with the reduction of carbon dioxide to carbon monoxide, there are absorption of heat and a fall in temperature.

  When the water is turned on, a drop of water is caught up by the air and hurled in minute particles into a cavern formed by the hottest part of the fire. The natural repulsion between water and fire is enhanced in confined space, and an increase of at least 1,650 volumes takes place instantaneously. The water explodes, recoiling from the fire towards the front, or inlet side of the producer.

  Any excess of water falls by gravity to the bottom, and then rises again as vapour, encircling the fire from below. Such undecomposed vapour as is carried in the general movement towards the outlet, no matter where its conversion from liquid occurs, serves to assist in establishing what we may call Zone D.

Shroud of Vapour

  In this zone temperatures are again lowered by heat-absorbing reactions between carbon and water, and gas making is complete. In Zone E, the last zone, is any excess of water taking no part in chemical change. The general tendency is upward and away from the source of heat, cooling as it goes.

  Liberal excess of water will be found either condensing as rain in the upper reaches of the producer or hopper, or lying in the bottom as a pool. By this method an elastic aqueous envelope is formed round the fire by the circulation of the excess of water in one state or another. For efficient working this must exist, at least, as a shroud of vapour, parting slowly with its warmth to the shell of the producer. The concentrated flame is of a "tulip" form.

  When the gas has passed on through the outlet the moisture content depends upon the excess of water persistently fed, upon the maintenance of the envelope, upon the size of the fire (which is related to the demand made on the producer) and upon the size and intrusion of the outlet.

THE PRODUCER of the Koela producer-gas plant. Fuel is contained in a cylindrical hopper bolted on above the firebox. A small water tank and drip feed supply a vertical vaporizer and preheater, which are bolted to the side of the casing. At the top of the preheater is a blower, operated by turning a handle, to create a forced draught for starting.

  One of the chief chemical features of this type of producer is that temperatures are maintained at the highest possible degree where heat is most required. Again, little, if any water passes through the fire, and most of the water is applied to the outside of the fire, where products can be fixed rapidly to prevent their degeneration. Comparatively little carbon dioxide is formed. Every use is made of the tendency of warmth and vapour to rise, of clinker and liquid to fall, of states of water, of contraction of space, of insulation from heat and so forth. Time is saved throughout.

  The standard types of these producers are designed to make gas from any one of various types of fuel, namely, good anthracite, hard coke, well-burnt charcoal, suitable low-temperature cokes, or peat charcoal. The range of the process is wide. By increasing draught and temperature and reducing the excess of water, the mixture of gases is of high heat content suitable for internal combustion engines. On the other hand, a mixture containing considerable steam can be produced.

  On road vehicles these producers are provided with clinker gear operated by a handwheel. The clinker box consists of a drawer, partly plated over at the top, which is fitted under the producer, the connexion being airtight. The clinker falls through an opening in the bottom of the producer and through the gap in the top of the clinker drawer on to a platform. The handwheel turns a spindle that expands two links which lower the platform. The clinker door is then opened and the drawer is pulled out as far as the stop allows. The box is then emptied by raising the platform. If the stop is removed the drawer can be pulled completely out, so that the fuel remaining in the producer will fall into the casing and can be raked out, thus enabling the producer to be cleaned.

  The funnel of the tuyere is furnished with a wick which is soaked with paraffin carried in a small tank on the vehicle. To start the fire this wick is ignited with a match. The blower, which is started by an electric motor supplied with current from the battery of the electrical equipment of the vehicle, is switched on.

Gas Generation in Two Minutes

  The generation of gas then begins, and the quality can be ascertained by opening a test valve and igniting the gas. After a few moments the engine is started by the electric starter, the blower is switched off, and the drip feed turned on. The drip-feed control is coupled to the accelerator pedal so as to regulate the water supply in all conditions. Gas can be generated in from two to five minutes. A petrol system is fitted as an auxiliary for starting or for manoeuvring when the producer is not required.

  A feature of the installation is that the entire vehicle is designed for operation on gas so that it is virtually impossible to detect any external difference from a vehicle running on petrol. The producer on a 5-tons lorry, for example, is mounted in front of the driver's cab and is enclosed by the bonnet. The greater part of the specially built engine is under the driver's cab. The engine develops 55 brake horse power at 2,200 revolutions a minute, and has a compression ratio of 8 to 1.

  The gas is carried by a pipe which passes from the producer under the off side of the engine, where it is cooled, to the expansion chamber, which is a cylinder fitted with baffles and with a door so that it can be cleaned when necessary. The gas enters this cylinder in the middle and leaves by two tubes, gilled for cooling purposes, at either end of the chamber. These tubes carry the gas to the other side of the lorry, where the cleaner is fitted. The cleaner is divided into two compartments, each containing compressed sisal fibre. Each pad of fibre deals with half the gas flow.

DASHBOARD CONTROLS of a 2-tons chassis driven by producer gas. The two levers to the left of the steering column are used to control the air for the producer-gas plant. In the foreground are the electric blower and its rheostat, used only for starting up. The water drip feed is automatic. The chassis has a five-speed gear box.

  The gas has to pass through the compartments of the cleaner and is thus filtered through the sisal. Doors with quick-acting locks are provided to enable the sisal to be cleaned by shaking and to enable carbon and other matter to be removed from the cleaner.

  The outlet pipe from the cleaner passes to the blower, and then to the special induction pipe on the engine. In the branch above the blower are two valves which connect with a pipe outside the cab. One valve gives an adjustment of the air required by the engine for idling. The other is coupled to the throttle valve to give a fine adjustment of the extra air required by the engine under load.

  At the centre of the engine manifold is a double-faced change-over valve, and when it is desired to start the engine on gas, this valve is screwed down to shut off the carburettor and open the gas inlet. The blow-off valve is opened when weak gas is generated in the initial stages, and this is closed when the engine is started on gas.

  The storage capacity of the producer on this vehicle is 324 lb. with anthracite at 45 lb. per cubic foot, and the water consumption of the producer is about fifty miles to the gallon. The producer will operate efficiently from full charge down to about six inches above the air inlet.

  The tuyere is the only inlet for air in the producer. Whatever the demand for gas, the air always enters at high speed to ensure rapid combustion at high temperatures. Because of the concentration of heat near the tip of the tuyere the clinker is deposited below it in layers on the lowering platform of the clinker drawer. There is no grate and there are no firebars, and no firebrick lining is used.

  A 4-tons lorry was tested for four days in July 1936 under the auspices of the Royal Scottish Automobile Club, the distance run being 592 miles. Anthracite fuel was not used. For three days the fuel was a porous coke produced from coal in a low-temperature retort, and on the fourth day fuel carbonized from Irish peat was used. Both fuels were supplied in nuts about the size of small haricot beans. Both appeared to give the same volume of gas, but the gas from the peat gave superior results, which were more noticeable when the engine was pulling hard on hills on top gear. Fuel cost was forty-three miles for one shilling, the fuel consumption varying between 1.3 lb. and 1.6 lb. a mile.

Cheapest to Run

  Another vehicle operated by a Leeds firm is a 6-tons lorry, which makes regular journeys between Leeds and London on anthracite fuel at a cost of about one shilling for twenty-five miles. At the end of each journey of about 200 miles the clinker is removed and new fuel is sifted, a task which occupies one man for about half an hour.

  Tests have been made of a 32-seats passenger chassis equipped with a specially enlarged fuel hopper to give a range of 300 miles. On this vehicle the producer was installed at the back of the chassis. Normally the vehicle seats thirty-four passengers, but the space for two seats is occupied by the extra large producer. The water cooling for the tuyere, which is generally connected with the engine circulation system, is in this instance independent.

  In service, lorries operate successfully in all conditions of road traffic, such as those encountered when a vehicle crosses London - a test of flexibility. These lorries are as easy to handle as ordinary vehicles. In Rangoon several omnibuses are running on producer gas.

  In general, there is a great saving of fuel costs for producer-gas vehicles and there is also a considerable economy of lubricating oil. As the cost of operating heavy vehicles is of supreme importance to commercial firms and as the evidence shows that the producer-gas vehicle can be run more economically than any other type, the development of the producer-gas vehicle is of great interest.

  Also, as fuels such as peat, charcoal, anthracite and the by-products of coal distillation plants are used, an outlet is afforded for them. It is stated that the coal industry would be helped by the distillation of more oil from coal and by the use of the by-products to drive these vehicles. Alternatively, the use of peat fuel would enable more use to be made of the extensive deposits in Scotland and Ireland.

  Producer-gas vehicles have been in use in many remote parts of the world for years. Their development in more civilized countries is rapidly extending, and the mechanical improvements are of importance.

DRIVEN BY PRODUCER GAS, this 2-tons chassis was designed for service overseas. It is powered by a six-cylinder engine with a special aluminium head. The engine develops 55 brake horse-power at 2,400 revolutions a minute on producer gas. The producer is placed at the front of the chassis on the off side. Dual pipes carry the gas from the expansion chamber to the filter. The chassis has a wheelbase of 10 feet.

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