Page 31 - Mechatronics with Experiments

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INTRODUCTION 17
Four-stroke cycle internal combustion engines are also divided into two major cate-
gories: (i) gasoline engines; (ii) diesel engines. The fundamental difference between them
is in the way the combustion is ignited every cycle in each cylinder. Gasoline engines use a
spark plug to start the combustion, whereas the combustion is self-ignited in diesel engines
as a result of the high temperature rise (typical temperature levels in the cylinder towards
◦
the end of the compression cylce is around 700–900 C range) due to the large compression
ratio. If the ambient air temperature is very low (i.e., extremely cold conditions), the tem-
perature rise in the cylinder of a diesel engine due to the compression of air–fuel mixture
may not be high enough for self-ignition. Therefore, diesel engines have electric heaters to
pre-heat the engine block before starting the engine in a very cold environment.
The basic mechanical design and size of the engine defines an envelope of maximum
performance (speed, torque, power, and fuel consumption). The specific performance of
an engine within the envelope of maximum performance is customized by the engine con-
troller. The decision block between the sensory data and fuel injection defines a particular
performance within the bounds defined by the mechanical size of the engine. This decision
block includes considerations of speed regulation, fuel efficiency, and emission control.

1.1.1 Diesel Engine Components
The main mechanical components of a diesel engine are located on the engine block
(Figure 1.17). The engine block provides the frame for the combustion chambers where
each combustion chamber is made of a cylinder, a piston, one or more intake valves and

Intake and exhaust Engine block
Camshaft valves
Fuel injector

Cylinder

Piston

Connecting
Crank shaft
rod
FIGURE 1.17: Mechanical components of an engine block: 1. engine block, 2. cylinder, 3.
piston, 4. connecting rod, 5. crankshaft, 6. cam-shaft, 7. intake valve, 8. exhaust valve, 9. fuel
injector.