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That Hydrogen Content in Producer Gas

17th January 1941
Page 22
Page 22, 17th January 1941 — That Hydrogen Content in Producer Gas
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Which of the following most accurately describes the problem?

yOUR correspondent, E.P.W., of Coventry, is guilty of a delicate flattery when he attributes knowledge of the whole story to anyone connected with the producer-gas job. His dislike of the dynamometer test is regretted ; it is not shared by engineers with a reputation to safeguard, for it tells so much to the open mind. It is not only-a record of past achievement, but what is much more important, it shows what can be done in the future ; also it is the enemy of wishful thinking and wilful misrepresentation.

For instance it tells the man who fills the hopper with anthracite or coke that he is getting only 50 per cent.

of the power that he would obtain on petrol. It also tells him that the power is not increased by adding water to the fire zone, and it truthfully points out the lapses from power from time to time, and the gradual decline in power from lighting up to the finish of the run.

Such are the dynaTmometer facts ; they are complementary to road tests—never contradictory. Road tests confirm all the above facts—as faithfully recorded by the dynamometer. .

In between the fact of filling the hopper with coal and the only other fact as recorded by the dynamometer, of a 50 per cent. loss of power, are many possibilities, suppositions and opinions due to the complexity of the Operations and reactions, and of the resulting gases. I trs below to analyse the complexities and give some of the simple facts which go to produce the results as recorded.

What is Involved by the Complex Character of the Gas

First of all, producer gas is a complex gas, consisting of hydrogen, carbon monoxide and methane. The flame speed of the component gases varies in the ratio of 7 to 1. What ignition timing can possibly meet such differing conditions? What compression ratio can meet them? Further, the flame temperature of the gases varies between 580 degrees C. and 750 degrees C. Also the calorific value Of the explosive mixtures varies between 79.6 and 94.7 per B.Th.11./cubic ft. Added to these facts the gas is being used in a petrol engine, quite unsuitable for its efficient combustion.. What possibility is there of estimating the effects of an increase of hydrogen, or for a matter of that, of methane or carbon monoxide?

Further, there is the variation in the quality of the fuel from one delivery to another, even from the same colliery.. There is a further variation in the moisture— natural and acquired on its journey from supplier to user —and independent of any injected moisture.

Then again there are the temperatures of the producer to consider. Until 900 degrees Cis reached, there is no carbon monoxide produced, only incombustible carbon dioxide. And yet hydrogen and methane are produced at much lower temperatures.

Tar is distilled from the fuel at between 600 and 750 degrees C. It is destroyed and therefore rendered harmless at temperatures between 1,150 and 1,300 degrees C.

Clinker is a necessary 'evil of producer gas; it is fused ash, wh.ch is produced at between 1,250 and 1,400 degrees C. Clinker formation interferes with the draught through the fire and reduces gas formation. Drivers know this by reason of the lever wangling they have to do to keep going. Their views on this point are fervent. The air/gas ratio varies with the load on the engine, calling for further lever wangling.

Then after the gas is made there is the matter of making it suitable for use in the engine. Its temperature is in the region of 900 degrees C. as it issues from the producer. It is wanted in the engine at as near atmospheric temperature as possible, involving a very considerable volume decrease and loss Cif heat. What happens to the individual gases under these circumstances? Then there is the impedance to the passage of the gases to the engine to persuade them to "drop the bone "—the dust and grit that wear out the cylinders of the engine.

Performances Show Variations in the Value of the Gas Observed performances on portable producer plants

show a variation in the calorific value of gas of between 155 and 92 B.ThiUsteubic ft.—from 100 per cent. to 60 per cent. Again drivers will express confirmatory views—very—on this point:

After having descended.a long hill when the accelerator

is depressed, there is no gas. During the descent the reduced draught through the fire brings down its temperature below the MO degrees necessary to make combustible gas and if there be water injection to the fire zone, this brings it down lower still.

There are suitable and unsuitable duties for producer gas vehicles. If performances of vehicles on suitable duties be used as general recommendations there are bound to be troubles. From opinions expressed by users of gas producers it would appear • that some such things have happened, to the detriment of the whole movement.

To return to the hydrogen content; all these points have a bearing upon it. I have referred to the numerous properties of the various gases nsed under considerably differing speeds and diversity of loads; I have not attempted to explain what happens, but leave it to

F.P.W. to put the fretwork together, but I ask him to remember that the dynamometer is the final arbiter of

all theories put forward. • AZOTE.

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Locations: Coventry

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