Diesel Musings

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1102 Box Canyon Road Fallbrook, California 92028

This little visit is to dwell upon some of the wondrous developments of internal combustion engines during that innovative period near the turn of the century when many people wondered if there would really be any other prime moving power to relieve the loads placed upon the old steam engines during that period.

You may recall that much experimenting had been conducted with early 'gas' engines, some of which burned natural or artificial gas, as well as vaporized liquid fuel oils. But these forerunners usually relied upon breaker points or spark plug points within the cylinder to ignite the gas sified fuel charge at the beginning of each power stroke. Both 'carburetion' or vaporization of the liquid fuels as well as the sparking ignition apparatus were the big stumbling blocks in these early attempts to do away with steam boiler response time, low efficiency, and water impurity troubles which gave rise to higher maintenance problems. Steam was still most reliable, of course, and is just about that even today.

But we must doff our hats to the English, French and German engineers in those early works. The Italians were not far behind. So it was at that time that Rudolph Diesel of Germany gave birth to the idea that a gaseous charge within the working cylinder could be ignited by the adiabatic heat of compression. Or nearly to that point as we shall see. He must have studied the phenomenon of production of heat as a byproduct when a gaseous substance was suddenly compressed within a closed cylinder. We youngsters discovered that when pumping up our old bicycle tires by hand; but we did not carry the idea beyond. Rudy's 'invention' was so promising that it has been attributed to the cause of his 'mysterious' disappearance while travelling to England from Germany to discuss his works before a society of engineers. His idea lived on to a perpetual commemoration of his genius.

Oil was not so common in Rudy's day, so he had contrived to utilize coal dust in his first engine. The principle was simple: he merely compressed a charge of air in his engine until sufficient heat was generated to ignite a measure of coal dust that was blown into the cylinder at the beginning of the power stroke. Now that was a real 'solid injection' engine, also of the 'air injection' type.

It is not my intention to discuss the mathematical and physical equations relating to the amount of heat raised during such compression cycles, nor the measure of terminal pressures arrived at, since these have been previously discussed in various articles. Suffice it to say that, if the volume of an enclosed gas is suddenly halved, its terminal pressure will not simply be doubled, but increased by an exponential value depending upon the nature of the gas itself. For we are doing work on the gas by compressing it, and that work must also show up as an accelerating factor. If the work is sudden enough to prevent loss to the enclosing container, the compression is said to be adiabatic. If the work is slow enough to allow absorption of increased heat to the container, we are in the realm of isothermal compression, which would result in a lower final pressure and of course no rise in temperature to ignite any fuel charge.

We find that, for sufficient ignition temperature in such engines, an actual compression ration comes to about 22 to 1. This yields a final pressure of approximately 500 psi gauge. Thus, following up on Rudy's original conceptions, air injection engines required a sufficient injection pressure to assure blowing of the liquid or solid fuel into the cylinder against the terminal compression pressure by an excess of some 100 psi. In present day power plants we find in utilizing this type of engine that the injection 'bottles' carry about 600 psi, while the starting bottles may carry up to 100 psi for reserve; since these engines are usually started by air pressure also. Thus each cylinder usually has at least four valves: the air intake, the exhaust, the fuel check, and the starting valves. A pressure relieve and auxiliary valve/plug is also usually incorporated. The latter may have provision for insertion of a burning cigarette or other 'punk' to assist in ignition in event of real cold inlet air temperature when starting.

In this type of engine, the fuel charge is distributed to the fuel inlet valve during the exhaust stroke of that cylinder. This allows sufficient time to help avoid drizzle, etc. The 600 psi injection air pressure is of course on the engine all the time. The air injection valve must begin opening then at the beginning of the power stroke. The exhaust valve operates conventionally, while the starting valve is cam operated only during that initial period of turning the engine over. The injection pressure must not be maintained too high above 600 psi, else the added cooling effect of its expansion down to 500 psi may cause starting problems.

But now we come to 'hot build' types of 'semi-Diesel' engines. To avoid such high compression pressures, designers cut the compression to approximately 225 psi. This necessitated additional heat for fuel ignition, which was secured initially by torch heating an uncooled portion of cylinder head projection or appendage. After starting, this uncooled bulb retained enough heat to continue ignition. These engines were also called 'hot' head engines; and no doubt many engineers became likewise over starting problems.

Another development to simplify construction and operation was the introduction of so-called 'solid-injection' principles. This term is a misnomer, but it stuck, like nominal plumbers' pipe threads and diameters, as well as many electrical and other mechanical mistakes. We find this in smaller Diesel type engines, and now particularly in automotive power plants all the way from cars to locomotives. In this sort of engine, which cannot burn its fuel so efficiently and cleanly as the air-injection type, we find that, while the terminal compression pressure still is about at 500 psi, the liquid fuel is mechanically injected at the beginning of the power stroke. The fuel injection pressure at this moment may be up in the several thousands of psi for its time of duration is very short in the comparatively high speed engine. Note, I have called out a misnomer. Elements are normally declared to exist in three physical states: gaseous, liquid, and solid. Now, other than Rudy's coal dust engines, by no means can fuel oil be described as 'solid.' But we are stuck with it.

Next comes another deviation of the solid injection engine for tractor purposes. This consists of substituting a spark plug with all its accoutrements in lieu of the hot bulb. We have quite a combination of the regular gasoline engine with the Diesel engine. And some farmers have found favor with them, while others have even sworn off drinking.

Oh yes; I might have mentioned that, aside form an auxiliary air compressor plant in the case of the air injection power plant, the pressures are maintained during operation by a three-stage compressor built in as part of the engine itself.

I have worked with, and studied Diesel engines for some sixty years, along with my regular and principle electrical engineering work. At age 81, I find both as interesting and intriguing as ever. At one time during the Great Depression, I even had a hand in teaching Diesel engineering in a prominent vocational school. And of course I am very proud of my steam railroading experience while yet a very young chap; for at one time I could shovel thirty-five tons of coal during an eight-hour period. The dear old railroad shops were at a division point of the C & NW, where engines running to the east burned coal; while those destined westward burned oil. How many times I crawled into hot fireboxes when, if one would spit on the grates, it would boilingly flash up into your face!

My first Diesel experience followed closely thereafter, when I became operating engineer during construction of one of the newer highway bridges across the Missouri river. The engine driving the all-necessary air compressor was probably the finest I have ever seen,a Worthington three-cylinder 'solid injection' job. This remarkable animal was a two-stroke design; but unlike the crankcase compression variety, had a lower cylinder head and seal together with crossheads, similar to a steam engine. The exhaust ports were simply openings in the lower portions of the vertical cylinders; while the intake valves (one into the enclosed lower cylinder head space, a second from this compression space to the lower port of the cylinder) much like conventional two-strokers. In this construction, the force is continually downward on the piston rod and connecting rod. An engine of this type was known to continue operation without trouble with a broken piston rod. Not until shutdown and inspection was the break discovered. Also, this design operated without the detonation knock so common in automotive engines. For the terminal combustion pressure was not allowed to rise considerably above that necessary for fuel ignition. One of those engines had established a world record for continuous faultless operation in those dear old daysover a year as I recall!

My greatest embarrassment during this particular experience was while performing a cleanup maintenance during a shutdown spell, I installed three of the 'feather' intake valves backwards (they were mounted in reversible grid plates). Try, try, again. Then the super came in, and we both proceeded to light cigarettes and stuff the burning butts into the auxiliary starting plugs, but still no run. It was only after much puzzlement upon the parts of both the super and myself, that we finally removed the valve grid retainer covers and discovered my foolish error!

In closing, it may be worth mentioning that, while in big stationary Diesel power plants the combustion pressure is controlled to very little more than ignition pressure, the practice in small automotive work is to run the combustion pressure up similar to that of the gasoline explosive types. This gives rise to the 'ungodly' clanking noise which is enough to drive most people away from the Diesel powered cars, in spite of their higher efficiency. So now, good bye, good fellows, until I may be moved to write again. (I am anxiously awaiting arrival of the new computer with its most remarkable convenience of 'word processor').