portion of figure 1.5, that the piston itself closes the intake port on this stroke.
Air ordinarily enters the cylinder at atmospheric pressure. The amount of fuel entering the
cylinder is therefore limited because it has to be related to the amount of oxygen available to mix with it.
If too much fuel enters the cylinder and is left unburned, it settles on the cylinder wall and piston and
dilutes the lube oil film. This prevents a tight fit and causes leakage of air and loss of power. Therefore,
the amount of entering fuel must be carefully regulated. Also, it must enter the cylinder so that the first
fuel entering begins burning before the rest of the fuel enters, providing gradual, even combustion. If all
the fuel enters the cylinder before ignition begins, it all burns at once--explodes--and a loud knock from
the explosion, called combustion knock, occurs.
A pressure-charged engine provides a method of putting more air, more fuel, and resulting
greater power into the cylinder. By this method, sometimes called supercharging, power can be
increased 50 percent in a four-stroke engine and 35 percent in a two-stroke engine. Extra air is made to
enter the intake valve or intake port by compression. A number of air-compressing devices have been
used to furnish supercharging air. The kind most commonly used on diesel-electric locomotives is the
turbine compressor, operated by a gas turbine in the exhaust system. It is the most logical place for this
turbine because a great deal of energy is wasted through exhaust of burned gases. Heat balance figures
show the loss to be as much as 40 percent of the energy liberated from the fuel by combustion. This
energy is captured to run the turbine which is connected to the compressor that delivers air under
pressure to the engine.
The fuel system, often referred to as the heart of the diesel engine, squirts the proper amount of
fuel into the cylinder at the proper time. The most important part of the system is the injector, which
measures out the right amount of fuel, injects it into the cylinders under high pressure, and reduces it to a
fine spray. Other parts of the fuel system are a tank to hold the fuel; a fuel-oil pump, driven by the
motor, to get oil from the tank to the injectors; filters to clean the oil as it passes through the system; an
injection nozzle to direct fuel into the combustion chamber in the best pattern