HOW A DIESEL ENGINE WORKS
A diesel engine is very similar in build to a gasoline engine with the exception of of being built heavier in all respects to contain the much higher than that of a gasoline engine.
The four cycle diesel even uses the same 4 cycles of the Auto Cycle engine. These cycles or strokes are the Intake, Compression, Power and Exhaust. The main difference in a diesel is that it has no sparkplug to ignite the fuel. The diesel engine uses the extreme heat generated by compression of air in the cylinder to ignite (Boyle's law ) the fuel when it is sprayed under 2000psi + in to the cylinder in a very fine mist just before top dead center on the compression stroke. The fuel meets the extreme heat and ignites.
Gasoline compression ratios stop around 12:1 ( 1/12 th the starting volume) Diesel compression ratios start 12:1 and go in to the high 20s. This is why diesels have to be built heavy in order to take the heavy mechanical loads of compressing it's air charge to a much higher pressure than that of a gas engine. If an engine is built big and heavy it must turn slower than it's lighter gas counterparts due to having to change the direction of heavier reciprocating members.
The Invention
Rudolf Diesel invented the first working prototype of the engine that bears his name on August 10, 1894 In Augsburg Germany. As a student he was festinated by an ancient concept of a fire starter.
This fire starter consisted of a small cylinder and a piston on a rod with a handle a plug screwed in to the end of the cylinder with a clip on it. This clip held a small tinder made of paper or dry cloth.
The piston was drawn back an pushed back in sharply the heat of compression would ignite the tender. The devise he was exposed to in school had a clear cylinder. Rudolf was trying to build an engine that used all the heat it made or 100% thermal efficient. He did not accomplish this but as with James Watt and the steam engine he did make a revolution in the internal combustion engine. In a diesel engine the fuel must first enter the cylinder and vaporize. Then it must mix with oxygen. This must all before it ignites. The time from entry to ignition is called ignition delay. The better the fuel is atomized the better the fuel and hot air mix together and vaporize the fuel. There are two factors that control ignition delay vaporization and atomization. The reason diesel was able to make it work as well as he did is that he used high pressure air to force the fuel in to the cylinder and in the process atomized it very well and made ignition delay more or less predictable. This was 1894. Diesel engines were large stationary or marine units that had a large air compressor for atomization air. They did find them selves well suited for submarine uses as they compressed large quantities of air for ballast control.
In 1913 a man by the name of James McKechnie pioneered Solid Injection but Robert Bosch of Stuttgart Germany is credited for mass producing in a practical form in 1925.
An injector very like the ones on the Lister type engines
click
for large pic
block diagram of a simple diesel engine
inside a fuel injector pump
Fuel shown in red comes in under high presser and applies hydraulic force to the needle and compresses the spring opening the seat in the bottom of the nozzle and allowing fuel to enter the cylinder in a highly atomized condition. This atomization is important to mix the fuel with air and go off at the correct time.
Shown below is the inside of the Mico fuel injection system like on Lister and Petter engines
developmental phases of port helix injection
Fig A Fig B Fig C
Fig C
Note the spill port is plumbed back around to the fill port The plunger is driven up and down by a cam lobe and a tappet that extends from the engine to the plunger in the bottom of the pump.
In 1909 a Frenchmen by the name LaOrang patented a device known as a precombustion chamber
Engine cooling Hopper
Thermal Siphon Tank Cooled
Since our Lister type engines are about the simplest diesel engine around my examples are of them. I use these engines in my job as a teacher to teach basic engine theory, high presser fuel injection and governor theory. They are a wonderful teaching tool.
Check back soon. under construction