Diesel Engines Summary



The compression ratio is the volume of the cylinder with piston at
TDC divided by the volume of the cylinder with piston at BDC.
Bore is the diameter of the cylinder.
Stroke is the distance the piston travels from TDC to BDC, and is
determined by the eccentricity of the crankshaft.
The combustion chamber is the volume of space where the fuel air mixture
is burned in an engine. This is in the cylinder of the engine.
The following components were discussed and identified on a drawing.
a. Piston and rod
b. Cylinder
c. Blower
d. Crankshaft
e. Intake ports or valve(s)
f. Exhaust ports or valve(s)
g. Fuel injector
ME
The crankcase is
defined as the area around the crankshaft and crankshaft bearings.-
The oil pan collects and stores the engine's supply of lubricating oil. Large
diesel engines may have the oil pan divided into several separate pans
The piston transforms the energy of
the expanding gasses into
mechanical energy.
Piston rings function as the seal between the piston and the cylinder wall and also act to
reduce friction by minimizing the contact area between the piston and the cylinder wall.
The rings are usually made of cast iron and coated with chrome or molybdenum. Most
diesel engine pistons have several rings, usually 2 to 5, with each ring performing a
distinct function. The top ring(s) acts primarily as the pressure seal. The intermediate
ring(s) acts as a wiper ring to remove and control the amount of oil film on the cylinder
walls. The bottom ring(s) is an oiler ring and ensures that a supply of lubricating oil is
evenly deposited on the cylinder walls.
The connecting rod connects the piston to the crankshaft

Crankshaft

The crankshaft transforms the linear motion of the pistons into a rotational motion that
is transmited to the load. Crankshafts are made of forged steel. The forged crankshaft
is machined to produce the crankshaft bearing and connecting rod bearing surfaces. The
rod bearings are eccentric, or offset, from the center of the crankshaft as illustrated in
. This offset converts the reciprocating (up and down) motion of the piston into
the rotary motion of the crankshaft. The amount of offset determines the stroke (distance
the piston travels) of the engine (discussed later).
The crankshaft does not ride directly on the cast iron block crankshaft supports, but rides
on special bearing material as shown in Figure 7. The connecting rods also have
bearings inserted between the crankshaft and the connecting rods. The bearing material
is a soft alloy of metals that provides a replaceable wear surface and prevents galling
between two similar metals (i.e., crankshaft and connecting rod). Each bearing is split
into halves to allow assembly of the engine. The crankshaft is drilled with oil passages
that allow the engine to feed oil to each of the crankshaft bearings and connection rod
bearings and up into the connecting rod itself.
The crankshaft has large weights, called counter weights, that balance the weight of the
connecting rods. These weights ensure an even (balance) force during the rotation of
the moving parts.

Flywheel

The flywheel is located on one end of the crankshaft and serves three purposes. First,
through its inertia, it reduces vibration by smoothing out the power stroke as each
cylinder fires. Second, it is the mounting surface used to bolt the engine up to its load.
Third, on some diesels, the flywheel has gear teeth around its perimeter that allow the
starting motors to engage and crank the diesel

Cylinder Heads and Valves

A diesel engine's cylinder heads perform several functions. First, they provide the top
seal for the cylinder bore or sleeve. Second, they provide the structure holding exhaust
valves (and intake valves where applicable), the fuel injector, and necessary linkages. A
diesel engine's heads are manufactured in one of two ways. In one method, each
cylinder has its own head casting, which is bolted to the block. This method is used
primarily on the larger diesel engines. In the second method, which is used on smaller
engines, the engine's head is cast as one piece (multi-cylinder head).
Diesel engines have two methods of admitting and exhausting gasses from the cylinder.
They can use either ports or valves or a combination of both. Ports are slots in the
cylinder walls located in the lower 1/3 of the bore. See Figure 2 and Figure 3 for
examples of intake ports, and note their relative location with respect to the rest of the
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DIESEL ENGINES DOE-HDBK-1018/1-93 Diesel Engine Fundamentals
engine. When the piston travels below the level of the ports, the ports are "opened" and
fresh air or exhaust gasses are able to enter or leave, depending on the type of port.
The ports are then "closed" when the
Figure 8 Diesel Engine Valve
piston travels back above the level of
the ports. Valves (refer to figure 8)
are mechanically opened and closed to
admit or exhaust the gasses as needed.
The valves are located in the head
casting of the engine. The point at
which the valve seals against the head
is called the valve seat. Most
medium-sized diesels have either
intake ports or exhaust valves or both
intake and exhaust valves