IS COAL THE ANSWER?
Page 48
Page 49
If you've noticed an error in this article please click here to report it so we can fix it.
How many millions of tons of coal lie beneath the surface of the earth cannot easily be estimated but we can be sure that there is sufficient to meet man's need at the present rate of consumption for a very long time. Can this solid fuel be readily converted to augment our dwindling automotive fuel supplies?
In this article Perkins Engines looks at the internal combustion engine and the prospects for the future in the face of dwindling fuel supplies.
DWINDLING world supplies of liquid fossil fuels upon which the internal combustion engine is dependent means that energy usage, particularly for automotive-type a ppl ications, must be re-assessed.
The short term objective must be to extend as far as possible the supplies of liquid fossil fuels. In the longer term a nuclear hydrogen-based economy is feasible.
There is a worldwide preoccupation with the "status quo" and operators' needs, coupled with the passive attitude of regulating bodies and potentially influential industrial sectors have produced an environment which favours only piecemeal dieselisation and degradation in the quality of the more energy-efficient fuels.
Perkins Engine•, believes it has a responsibility to icp lead the way towards a clear-cut policy, because the present lack of such a policy will, in the long run, endanger fuel conservation, misuse technical resources, lead to poor production continuity and escalate production costs.
An examination of oil refinery practices and processes in relation to the internal combustion engine leads to the conclusion that so-called "wide-cut" fuels should be preferred to the cur rent distillates. An injected stratified charge engine able to operate economically on widecut fuels derived from refineries and the world's extensive coal resources would be preferred to the conventional gasolene or diesel unit.
Wide-cut fuels
Wide-cut fuels are distilled in oil refineries by a similar process to that for ordinary fuels. It involves heating the crude in a cylindrical column or "fractionating tower", which causes the separate groups to rise like steam as they are heated above their boiling points. They are drawn off separately at appropriate points at the side of the column and condensed to liquid.
The groups from this first distillation can be simply, classified from the top of the column downwards in order of decreasing volatility — as light distillates, middle distillates and residue. In the early days, light distillates from some crudes were suitable for use as petroleum spirit (gasolene) after little subsequent treatment and the middle distillates, known as gas oil, could and still can be used in diesels.
As the gasolene engine became more complex and demand for the fuel , increased, many more proceses were introduced to cater for the quality and quantity of the demand. The production of distillate fuel for diesel engines, however, has' remained simple.
From every ton of crude oil, refineries have considerable scope to produce variations in the proportions of the finished products. An adjustment in the range of distillates can produce a high proportion from crude of a "wide-cut" fuel, which can be defined as an extension of the middle distillates to include more of the light distillates and of the residue (if "cracked" to smaller molecules).
Wide-cut fuels is a definition that can also be applied to the liquid fuels that can be derived from coal.
The injected stratified charge engine
The injected stratified charge engine (SCE) is often referred to as the "spark assisted" diesel engine — it would use sparking plugs to provide spark ignition. A diesel engine is no more than a stratified charge engine with compression ignition.
There are two types stratified charge engine. ca uretted and injected fuel int duction. The injected SCE preferred for several reasons. El it can operate on both wit cut refinery fuels and on vvii cut coal-derived liquid fuels LI the energy from a barrel crude oil is expended both the engine and by the refini process. One unit of energy pencled by a petrol engine neE six or seven units fed into engine, and to obtain this frt the refinery as gasolene requi another 1.3 units — totalli eight. The equivalent for a ca uretted SCE is 7.1 and foi diesel and an injected SCE i. only 6.2
thermal economies of I diesel engine have been am proved. Published performar data for the injected SCE sh that it is capable of equalli these thermal equalities usi several combustion systems I] the addition of these "o% the-road" economies to the energy-demanding diesel f suggests that the injected SCI capable of yielding import, economies of natural enei resources
E gasolene has octane ratir and diesel fuel, cetane ratings which are directly inverse octane ratings — and art measure of the ease of spc aneous ignition of the fuel. a ratings complicate matters, I they affect economy, exha quality and noise. Wide-i fuels for use in the injected S. are cheap to produce becai they eliminate the complicat of cetane ratings.
Cetane rating scatters widening, end boiling points rising and aromatic content creasing. The resultant hig noise and nitrous oxide cl tributions, adverse impacts exhaust clarity, increases sooty formation and unbu hydrocarbons are being cate for by piecemeal prod modifications with frequent uneconomic specificat changes. This endangers fuel )nomy, misuses technical ources, leads to poor proction continuity and escang production costs.
A new dimension to the leral confusion will be added future and pending envir mental legislation on rticulates, polynuclear imatics, sulphur and odour cies
le alternatives
The injected SCE, together h the introduction of wide-cut provide a logical and ional plan for the develop!nt of automotive-type enes over the remainder of the th century, based on the need minimise wastage, or liquid sil fuels.
At this stage alternate prime ivers such as gas turbines ayton cycle) and Stirling enies can be discounted be„Ise their large scale introducn within the time scale in estion would seem unlikely. is judgment is based on the :Ld for a major breakthrough ceramic technology to render her engine economically tipetitive.
The breakthrough is needed cause, for maximum iciency, the heater head of a rling engine, or the turbine of as turbine, must operate at h temperatures. The higher temperature, the higher the rmal efficiency. The answer uld be to replace metals with amics so that you can work at se higher temperatures. However, ceramics are brittle
crack under thermal ling, so more adaptable cerics must be found to make it rk. This is the problem. Even en the breakthrough, ether with substantial public
funding, the lead time available is probably inadequate and there is a need for heavy capital investment.
Rankine cycle engines are not likely to emerge as significant due to low thermal efficiency.
Brayton and Stirling Cycle engines would however appear to be front runners in the subsequent stage, with liquid fossil fuels essentially depleted and a progesssive switch to .an hydrogen-based economy. Reciprocating engines have poor power densities when burning hydrogen-based fuels.
The longer term Improved fuel economy, reduced quality requirements and maximum fuel availability from crude oil inherent in the use of wide-cut fuels and the injected SCE offer significant reductions in the depletion rate of liquid fossil fuels. Without placing restrictions on the size, number and use of these vehicles, the improvements recommended may still not give sufficient time for the evolution of the hydrogen-based economy before reserves of crude oil are exhausted.
It is prudent therefore to examine the possibility of exploiting the world's large coal reserves. Liquid fuels from coal are not new. They contributed significantly to World War II supplies in both Germany and the UK_ They are currently used in South Africa.
At present, all practical activities and technical studies of coal resources and their conversion to liquid fuels are obsessed with the need to satisfy the exacting demands of the inefficient gasolene engine.
This illogical stance reduced the thermal efficiency of coal conversion to gasolene to 30-40 per cent. Exactly the same situation would arise with the conversion of coal to methanol — another fuel project of which much has been heard. This again is an uneconomical project due to the low thermal 'efficiency. A fuel suitable for the injected SCE and still complying with necessary fuel specifications, would, however, raise the conversion efficiency to 70 per cent.
Current problems
The current world energy scene presents a picture far removed from that which Perkins considers the correct path to follow. Governmental activities expressed through fiscal policies, road speed regulations and environmental legislation have been notable by their ab-' sence, obscurity, fluctuation between extreme pressure groups, and political expediency.
The United States, currently representing about one-third of the total world energy demand has so far failed to reconcile environmental and energy needs successfully, with the twin initiatives of Nixon and Carter sandwiching a long period of near-inactivity on the energy front in the face of escalating petroleum usage.
The automotive industry as represented by the major US companies, obsessed with the need to meet progressively tighter exhaust quality standards quickly has been reluctant to adopt new developments.
The major oil companies, the industrial sector with the greater influence, accept the case for a wide-cut fuel technology but discourage progress by their passive stance and reluctance to alter investment and marketing strategies unless forced to do so by regulation.
The regulating bodies have shown almost total lack of interest.
By default the situation has fallen into one of haphazard creeping dieselisation coupled with a gradual degradation in diesel fuels. Some developing countries are experimenting with vegetable oils and vegetable derived alcohols as "extenders” for liquid fossil fuels. However, vegetable oils are very corrosive and carbon forming, and alcohols are very expensive.
Conclusion
The forecast depletion rate for liquid fossil fuels suggests the need for a comprehensive energy conservation programme. Current preoccupation with the gasolene engine is perpetuating the need for highgrade distillate fuels requiring energy-wasting refinery processes.
The conversion of automotive-type applications to injected stratified charge engines would significantly improve "over-the-road" efficiency and allow the production of wide-cut fuel oils as the primary refinery take-off. Such an engine-fuel combination would minimise procession wastage and maximise crude barrel yield. Similarly, conversion of coal to a wide-cut fuel rather than gasolene or methanol would greatly improve the overall thermal efficiency of the process.
In the longer term, an hydrogen-based economy would appear likely, the fuel being burned in a Brayton or Stirling cycle engine.