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A breakthrough for methane?
Page 80
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Liquid methane as an intake air refrigerant might bring big power gains AS A RESULT of the fuel crisis, the status of the diesel as the most efficient power unit for vehicles has become impregnable and is likely to remain so for decades. And any talk of exploiting alternative fuels over the next 20 or so years is generally dismissed by technicians of the commercial vehicle industry as impracticable or undesirable unless it applies to fuels for diesels.
Although anything could happen to oil supplies if there were another Middle East war, it is now assumed that OPEC has seen the light, albeit dimly, and will be begrudgingly reasonable in its dealings with user countries. So there's a breathing space for developing better diesels.
While the stated opinions of leading authorities on offshore oil and gas availability have been contradictory with regard to overall reserves, notably on the prospective output over the coming years of North Sea gas (which mainly comprises methane or natural gas) some say it will be surplus to industrial and domestic requirements long after North Sea oil has dried up. And it could be that methane is the most promising of all alternative fuels for diesels.
Marsh gas Methane was once known as marsh gas and unlike hydrocarbon oils it is being continuously generated in very large quantities by the decom position of organic matter, as evidenced by the yield of gas at sewage plants which is employed to run dual-fuel industrial diesels. At the risk of being conceptually idealistic the conversion of a waste material generated day-by-day by natural decay into a highly useful fuel might well be cited by an environmentalist as a process which could serve the human race indefinitely without exhaustion of resources.
It may be pertinent to note that there is a superabundance of natural gas in Siberia and that new discoveries nearer home are probable. And it is said that enough methane is produced on a typical farm to run the farmer's tractors and family cars as well as lighting, heating and power systems. So exhaustible supplies could initially be augmented by, and later replaced by gas from inexhaustible sources. The more people there are in thc world the greater will be the production of methane by natural means.
A relatively large number of industrial engines and some vehicle power units are operating on methane, and in the case of vehicles it is necessary to carry it in liquid form at a very high pressure in heavy cylinders, which exacts a normally unacceptable payload penalty, or to store it on the vehicle in an insulated cryotank at a temperature of —160'C (-256'F) following purification and processing in a cryogenic plant. Such a plant is costly to install but according to current reckoning the system might at some future date make economic sense as an isolated project if a large fleet were operated in a limited radius and the vehicles returned to base for refuelling.
So the prospect of commercial application to vehicles on a worthwhile scale generally appeals as one of those things which might happen one day. It could depend on a breakthrough of some kind.
Storage While the hoped-for breakthrough is a means of augmenting the supply of methane economically and/or facilitating its storage on vehicles, improving its utilisation in diesels could be a big help, And this could take the form of conversion to methane injection and use of the fuel to refrigerate the intake air, the gas being stored in liquid form in a cryotank. According to reliable rumour this has been done experimentally in America and probably Russia, and it is said that the system provides an increase in output of 80/100 per cent !
As in the case of liquefied petroleum gas liquefied natural gas can readily be employed to fuel a sparkignition engine after mixing with air in an evaporator. And it can be used in a dual-fuel diesel in which pilot injection of a small quantity of dery initiates combustion of gas aspirated with the intake air. This is completely satisfactory in an industrial unit operating at a constant speed and power output and could be applied to a vehicle diesel (as has been done with LPG) with a gas proportion up _to, say, 40 per cent.
But part-load operation with more than a small percentage of gas is normally wasteful because of the amount of excess air required to maintain the rated compression ratio.
Many years ago there was talk of the benefits that could be derived from refrigerating the air of a diesel, but although a particular project known to the author had a promising start, a suitable type of refrigerating system was not available or could not be evolved and research work was discontinued. Pressure charging and charge cooling improve the power output of a diesel by pumping more air into the cylinders and increasing the weight of air py reducing its temperature. The weight of air could be at least doubled by refrigeration without a turbocharger or charge cooler. And a liquid gas stored at —160°C (-256°F) could also be used as a refrigerant.
Ideal for diesels A leading research engineer has pointed out that methane could be an ideal fuel for diesels. If, however, it were supplied in low-temperature liquid form the engine would have to have a very high compression ratio to facilitate starting and to promote efficient combustion at reduced loads. The results of early research work on refrigeration indicated that a big increase in power could be obtained without raising the mechanical stress levels of the engine unduly, although no information was available on its effect on fuel consumption.
Diesels of double the horsepower operating at normal peak pressures could make economic sense of establishing costly cryogenic plants throughout the country, although obviously authoritative reassurance of continued methane availability would have to come first.