The Physics of a Diesel Engine
The world we live in is surrounded by diesel engines. They are on the freeways, railways, airways, and are one of the leading electricity producers in the world. They are also becoming more popular in automobiles. These engines are efficient and reliable and they are getting very sophisticated. However, the physics behind these engines has not changed.
By way of definition, courtesy of Diesel Engine
Engineering: [a] diesel engine is an internal combustion engine in which the chemical energy of fuel is transformed into thermal energy of the cylinder charge, in consequence of the self-ignition and combustion of fuel in the engine cylinder after compression of the air charge in the cylinder (p1 Makartchouk).
There are basically two types of diesel engines, two-stroke and four-stroke. In a two-stroke engine the piston is forced from the top of the cylinder by the expanding air fuel mixture. Before the piston reaches the bottom of the cylinder the used mixture, (called exhaust), is forced out of the cylinder by the incoming fresh air. The fresh air relies upon a blower, air induction system, to propel it into the combustion chamber. During this time period the piston begins to travel to the top of the cylinder and compress the fresh air sufficient to raise the temperature in the combustion chamber, (area between the top of the cylinder and the cylinder head at top dead center), to 1000-1200 degrees Fahrenheit (p12 Dagel). The fuel is then injected under pressure into the combustion chamber, the air ignites the fuel and the gases begin to expand finishing one cycle.
A four-stroke engine begins the same way as the two-stroke with the expanding gases pushing the piston downward, called the exhaust stroke, but the air is not replaced at the bottom of the stroke. Instead the piston bottoms out and then on the way back up it pushes out the exhaust finishing two strokes. The piston then travels down pulling in fresh air, (third stroke), after the piston bottoms again it travels up compressing the fresh air, (fourth stroke). The fuel is then injected and one cycle is completed in 720 degrees or two full rotations of the crankshaft.
The disadvantage of two-stroke engines is their dependency on a blower to force air into the chamber and their inefficiency. A four-stroke engine does not have an expansion stroke every 360 degrees but it is more efficient because it has more time to completely burn the fuel injected into the cylinder.
There are mechanical and fundamental differences between the two-stroke and four-stroke engines but the physics remain the same. They both rely upon the compressed air to ignite the pressurized fuel and the resulting expansion for their power. At first glance it may look like the explosion in the chamber...