35640 Avenue F Yucaipe, California, 92399
I had just donned my kitchen apron after having returned from church last Sunday, and was poised before the kitchen window, overlooking Hubby’s ‘Back Shop’, when the sound of screeching nails being pulled from well seasoned boxwood crating sent shudders up my back. So I hastily put the cake in the oven, which I had just whipped up, and reaching for my shorthand notebook and pencil began a trek out back to see what was going on, and if possible abate the very un Sunday like noise.
Upon reaching the shop, I witnessed the last of the crating boards being removed to expose what appeared to be an old-fashioned coffee grinder like we had in the Country Store way back when I was in pig tails. But while our old grinder with its two large flywheels and central vertical hopper was painted bright red and trimmed in gold, this ‘grinder’ was in deep brewster green and looked like it was built substantial enough to grind anything up to gravel.
‘What are you adding to the museum, there?’ I quiered, and as Frank gave me a side glance while clearing away the packing he replied, ‘This is the latest import from Germany, a real little Diesel stationary engine intended to do the chores around the shop and farm, and even since the war there has been nothing like it manufactured in this country.’
‘So what?’ I countered, ‘What will it do that the old Fuller and Johnson cannot do?’ He was quick with the comeback, ‘Look, Mamma, No Plugs!’ ‘I can see it has no boiler, so what makes it run?’ I asked. ‘This is the latest stage in the development of the art in honor of Rudolph Diesel,’ he began, and continued: ‘Rudy’s original invention consisted of an engine following that utilizing the Carnot cycle as you may remember from your high-school physics. But Rudy went on to reason that if the compression pressure was raised high enough the resulting temperature would be high enough in the cylinder to ignite the fuel charge without benefit of a spark plug, igniter, or other device to start combustion of the charge in the cylinder. But this might result in erratic timing unless only air were compressed in the cylinder, and the fuel then injected only at the time when expansion of the enclosed gases should commence. Actually, Germany had lots of coal but no oil, so Rudy’s first engine was constructed on the principle of utilizing an air blast to blow a charge of coal dust into the cylinder against the high compression pressure at the moment of ignition. Whereas, the compression pressure was in the neighborhood of 450 psig, the air pressure necessary to inject this charge of coal dust into the cylinder was near 600 psig.’
‘Mr. Ed’ Case 25-45 cross-mounted tractor owned by Francis. It was in the homecoming parade in Girard, September of 1968 and at the Pioneer Harvest Show at Ft. Scott in October.
Photo by Myrl Hix, Pittsburgh, Kansas.
7 Hp. Galloway owned by Rayma Sevart of Girard, Kansas. Displayed at the Pioneer Harvest Show at Ft. Scott, Kansas, October of 1968.
Photo by Myrl Hix, Pittsburg, Kansas.
12 Hp. Associated and International Tom Thumb gas engines owned by Harold Morrell of Fulton, Kansas and displayed at the Pioneer Harvest Show.
Photo by Myrl Hix, Pittsburg, Kansas.
‘Well, I did get into light physics and algebra in high school, and remember hearing of thermo-dynamics,’ I said , ‘But where does all this high temperature for ignition come from?’ ‘Oh, it is not too difficult,’ Frank replied, ‘and goes something like this: In really there is no such thing ass ‘cold’ but cool and cooler are only terms of relevancy.’ ‘You mean 1 did not really need my sweater on last night when we were parked out in that Drive-in?’ I suggest ed. ‘You are just accustomed to personal comfort temperatures, and this engine which we will soon have running does not know whether it is hot or not, it someone does not discover engine language and tell it so,’ said Frank, and continued,’ You know, if everything were to really, become cold, there are those among the scientists who maintain that under such conditions all matter would cease to exist, as the elements of every molecule of all mailer would come to a dead standstill and cease to hold their relative orbits which distinguish one substance from another. But to get back to this subject of heat developed under compression. Just consider, that if we had a closed container like a piston in a cylinder, which was perfectly heat-insulated, and were to move the piston so as to reduce the volumetric contents lo one-hall its original size, the absolute temperature would then become doubled also. In this case we must start from the real ‘cold’ point which is 460 degrees be low zero Fahrenheit, same as we must consider absolute pressures from nothing. You realize, of course, that at sea level, for instance, we do not live at ‘zero’ air pressure, but actually are under approximately 14.7 psig pressure. The air pressure acts upon us from in side as well as out, so we do not feel any discomfort and to our senses it is only zero psig (gage).’
‘You have me pretty well framed in on generalities,’ I interposed, ‘How a bout a concrete example so that 1 may understand a bit more of what you are telling me?’ ‘You are always the good student, when no one else is around,’ replied Frank, and continued ‘Take that piece of chalk on the little blackboard hanging on the side of my locker and jot this down:
T2 (V1) k-1 (P2) K-l
—- = Tr = (—) = (—-) k
T1 ( ) ( )
(V2) ( P1 )
Now, in this simple bit of algebra, P1 represents our initial air pressure in the cylinder at the end of the intake stroke, which is zero as gages are calibrated for their usage, but in our case is really 14.7 pisa. Let’s consider for example that we will compress this air charge lo 450 psig which will then become 464.7 pisa; and at our ambient temperature of 70 degrees Fahrenheit (who should never have become mixed up in this business in the first place) T1 then becomes 460 plus 70 degrees or 530 degrees absolute. Now, aren’t you beginning to sweat a bit under such temperature?’ ‘Shux, go on, I’m comfortable,’ I replied, and Frank continued, ‘Well, T1 is the absolute temperature ratio, and ‘k’ is a thermodynamic constant which depends upon the type gas we are talking about. For air, k is equal to 1.4. Now, you were asking about ignition temperature, so let us substitute real values into the first and last terms of this equation and see what gives:
(464.7) 1.4-1
T2 = 530 (14.7) 1.4
= 530×31.5 0.286
Now, if you will recall your introduction to logarithms and trust my slide rule, this expression develops:
Log T2 = Log 530 plus 0.286 Log 31.5
= 2.724 plus 0.245 = 3.149
from which we read off antilog 3.149 is T2 = 1410 degrees absolute. And consequently the air temperature within the cylinder as read on the Fahrenheit scale would be 1410 – 460 = 950 degrees, which is sufficient lo ignite any ordin the above equation is an adiabatic expression which is derived from theory and measured and verified in the laboratory and allows for no heal loss to the cylinder walls, head nor pistons, which at slow cranking speed might become serious as time is of the essence.’
Well, I thought I might see if I could make him scratch his head, so I questioned, ‘Under the above conditions, what is the lowest ambient temperature under which such an engine could operate, using a fuel with a flash point of, say, 700 degrees Fahrenheit? But Frank’s mind was running ahead of me a bit as he replied, ‘We need only make the proper substitutions in the same equation and solve for T1 as a mini mum, but now that you have me fired up, let us consider what the adiabatic compression ratio results from what we have here. If V1 is our initial cylinder volume at end of intake stroke, and V2 is the volume of air at end of compression stroke, then according to the pro
V1 ( P2) 1
—- = Vr = (—- ) k
( )
V2 ( P1 )
which in our case reads:
(464.7) 0.713
(14.7 ) = 31.5 0.713
And the Log of our compression ratio becomes:
Log Vr = 0.713 Log 32.5 = 0.713 x
1.483 =1.06
And, again, solving for the antilog 1.06 on my rule, or you may check your tables, which might be a good idea, yields the result that
Vr = 11.5
Now this is true adiabatic as explained earlier, and since we do have some heat loss to the iron in the cylinder, this theoretical value might best be raised a bit. Actually, for instance, in such engines as the Cummins, the compression ratio is closer to 15 to one.’
‘Now, back to my Wesson Oil at 700 degrees Fahrenheit, I suppose you will be trying some of that,’ I tormented. ‘Oh yes,’ Hubby replied. ‘For this solutions, let us use the second and third terms of the original equation with which we started, and remember your 700 degrees Fahrenheit (there goes his name again unscientific scoundrel!) be comes 1160 degrees Absolute. Then:
1160 (11.5)1.4-1
——– = (—–)
T1 ( 1 )
= 11.5 0.4
And so T1 = 1160
——-
11.5 0.4
Or, Log T1 = Log 1160 – 0.4 Log 11.5
= 3.064-0.4 x 1.06-2.640
Once more, the antilog of 2.640 yields a T1 of 437 degrees Absolute, which, when subtracting 460 tells us that your oil will just flash at – 23 degrees Fahrenheit, or 55 degrees below freezing water.’
‘Well, that about takes the rag off the bush today,’ I declared, I think that I should send this in to GEM after all my shorthand notes and your slip stick efforts. All the readers may not fully understand your slight-of-hand but they should not question your library doubt less will be interested to read of some of the factors having to do with designing such a thing as a Diesel engine. You know, the most interesting thing to me was your explanation of having so many heat units an any particular specimen of air, for instance, when k = 1, and then doubling the sensitive temperature above temperature-nothing by simply compressing its volume to half-space. And if I were to reduce its volume to one-third original the absolute temperature rise would be three times’.
‘You are catching on better than I could do with that cake you just put in the oven,’ Frank said, and continued ‘But if you send this into GEM you better hand me down my clarinet, just in case that chap who plays the French horn up in Michigan may take exception. I will have to swab it out and be prepared to try drowning him.’ ‘Oh oh,’ I exclaimed, ‘you just reminded me of my cake and it looks like my forty-five minutes is up. Any burnt crust, -you will have to eat it!’
Pictured is a buckwheat flour mill during construction. It has been completed and works real well.
