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The I.C. engines can majorly be classified, on the basis of the type of ignition used, as: Both types can further be classified on the basis of the no. of strokes required to complete one complete thermodynamic cycle, thus the further classification can be:
Spark Ignition Engines: In the spark ignition engines, a mixture of air and fuel, called charge is compressed into a very small volume called the clearance volume. Then the charge is ignited with the help of an electric spark, exactly timed with the position of the piston in the cylinder. Commonly, the fuel used with this type of engines is gasoline oil or petrol. These engines are quantity governed by the opening and closing of a throttle valve which regulates the mass flow of charge to the cylinders. Some gas engines are throttled by alteration of the lift of the admission valve, and this can be controlled from the engines governor. The governed speed can be adjusted to select any value in its range. The petrol engine will operate on air-fuel ratios in the range 10/1 to 22/1, but not necessarily satisfactorily at the extremes. There is some variation between engines. Compression Ignition Engines: In the compression ignition engines, air is induced in the cylinder of the engine during the induction stroke. This air is then compressed into a small volume to a very high pressure (normally 60 to 140 bars). At this time the fuel is injected through a fuel injection nozzle, that sprays the fuel onto the compressed air at an even higher pressure. this causes the fuel to ignite producing gases with high temperature and pressure. these gases push the piston back making the power stroke. The difference between the two types is that of the fuel used and the method utilized for the ignition of the fuel. So the construction and working of the two and four stroke engines of both types is the same with the only difference that the spark plug of the S.I. engines is replaced by the injection nozzle in the C.I. engines. Now I will explain the construction and working of the two and four stroke S.I. engine. The same will be true for the corresponding C.I. engines with the only difference that in the C.I. engines, there will be an injection nozzle in place of the spark plug.
A Four Stroke Engines
FOUR STROKE PETROL ENGINES
Almost all cars currently use what is called a four-stroke
combustion cycle to convert gasoline into motion. The four-stroke
approach is also known as the Otto cycle, in honor of Nikolaus Otto,
who invented it in 1867. The four strokes are illustrated in Figure 1.
They are:
This animation also illustrates a simple
ignition system using breaker points, coil, condenser, and battery. Here is another figure, that illustrates the working of a
modren engine more realistically. In this engine model, the inlet and outlet
poppet valves are being operated by a single cam. The different parts and
strokes are shown in the figure.
Here's what happens as the engine goes through its cycle:
Now the engine is ready for the next cycle, so it intakes another charge of air and gas. The only different in a four stroke petrol engine and a four stroke Diesel engine is that the spark plug of the former is replaced by a fuel injector in the case of the later.
Rudolf Diesel developed the idea for the diesel engine and obtained the German patent for it in 1892. His goal was to create an engine with high efficiency. Gasoline engines had been invented in 1876 and, especially at that time, were not very efficient. The main differences between the gasoline engine and the diesel engine are:
The following animation shows the diesel cycle in action. You can compare it to the animation of the gasoline engine to see the differences:
Similarly the following Applet shows, how a four stroke diesel engine works
If the applet does not start automatically, click here to install java virtual machine
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