Diesel Musings


| September/October 1984



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.