between 1,800 and 30,000 psig. The fuel does not ignite immediately. There is a
delay period when the fuel droplets vaporize and reach their ignition temperature.
The extent of this time delay is affected by the design of the engine, the temperatures of the inlet air and fuel, and the degree to which the injected fuel is atomized
on entering the cylinder. This ignition delay must be kept as short as possible to
avoid accumulation of fuel in the cylinder before ignition. Such a situation causes
diesel knock when this large quantity of fuel detonates.
After ignition, fuel injection continues for a portion of the power stroke. This
fuel burns almost instantaneously with the remaining air and combustion products
in the cylinder. This more controlled burning period is referred to as diffusion
combustion. Fuel injection is stopped part way through the power stroke. Finally
the exhaust stroke purges the combustion products from the cylinder, and the cycle
begins again.
Design Improvements to the Basic Diesel Engine
Fuel injection improvements. Most diesel engines built in the 1980s were equipped
with indirect fuel injection system (IDI). Modern engines are equipped with
direct fuel injection (DI) which is designed for the geometry of the combustion
chamber and is significantly more efficient. (Note: This can be compared with
the direct injection concept in gasoline engines which was introduced around
this time also.)
Four-valve cylinder heads. This promotes better movement of both combustion air
and exhaust gases. This causes high turbulence of the fuel and air in the
combustion chamber, resulting in good distribution of the fuel and increased
flame speed which reduces the ignition delay time.
Electronically controlled fuel injection timing. This allows for the injection of a
small quantity of fuel before the main charge into combustion chamber. The
result is a quieter combustion, minimizing the amount of premixed combustion
and maximizing the more controlled diffusion combustion.
Increasing the amount of air introduced into the cylinder. Using a turbocharger,
which is an air compressor driven by a turbine using exhaust gas energy, the
mass of air introduced into the cylinder is increased. This enables the engine to
burn more fuel, thus increasing its power output. Using this concept, the power
output for a diesel engine can be increased by as much as 50 % for the same
engine displacement.
The Parameters of Diesel Fuel
The following are the major parameters in meeting the diesel fuel specification with
respect to engine performance and/or emissions:
• Cetane number
• Aromatic content
• Density
• Sulfur content
• Distillation
Petroleum Products and a Refinery Configuration
77
delay period when the fuel droplets vaporize and reach their ignition temperature.
The extent of this time delay is affected by the design of the engine, the temperatures of the inlet air and fuel, and the degree to which the injected fuel is atomized
on entering the cylinder. This ignition delay must be kept as short as possible to
avoid accumulation of fuel in the cylinder before ignition. Such a situation causes
diesel knock when this large quantity of fuel detonates.
After ignition, fuel injection continues for a portion of the power stroke. This
fuel burns almost instantaneously with the remaining air and combustion products
in the cylinder. This more controlled burning period is referred to as diffusion
combustion. Fuel injection is stopped part way through the power stroke. Finally
the exhaust stroke purges the combustion products from the cylinder, and the cycle
begins again.
Design Improvements to the Basic Diesel Engine
Fuel injection improvements. Most diesel engines built in the 1980s were equipped
with indirect fuel injection system (IDI). Modern engines are equipped with
direct fuel injection (DI) which is designed for the geometry of the combustion
chamber and is significantly more efficient. (Note: This can be compared with
the direct injection concept in gasoline engines which was introduced around
this time also.)
Four-valve cylinder heads. This promotes better movement of both combustion air
and exhaust gases. This causes high turbulence of the fuel and air in the
combustion chamber, resulting in good distribution of the fuel and increased
flame speed which reduces the ignition delay time.
Electronically controlled fuel injection timing. This allows for the injection of a
small quantity of fuel before the main charge into combustion chamber. The
result is a quieter combustion, minimizing the amount of premixed combustion
and maximizing the more controlled diffusion combustion.
Increasing the amount of air introduced into the cylinder. Using a turbocharger,
which is an air compressor driven by a turbine using exhaust gas energy, the
mass of air introduced into the cylinder is increased. This enables the engine to
burn more fuel, thus increasing its power output. Using this concept, the power
output for a diesel engine can be increased by as much as 50 % for the same
engine displacement.
The Parameters of Diesel Fuel
The following are the major parameters in meeting the diesel fuel specification with
respect to engine performance and/or emissions:
• Cetane number
• Aromatic content
• Density
• Sulfur content
• Distillation
Petroleum Products and a Refinery Configuration
77