The first example that I will
discuss is the ceramic turbocharger. Since the inventions of the internal
combustion engine mechanical and automotive engineers have been searching for
ways to boost its power. One way to add power was to build a bigger engine.

However, this wasn’t the best method as bigger engines will weigh and cost more
to build and maintain. A more appropriate way to add power to the engine was to
force more air into the combustion chamber.  Adding a supercharger or a turbocharger can do
this. These devices produce high-pressure air in the engine cylinders and thus
provide more fuel meaning a bigger explosion and greater horsepower. The main
difference between turbochargers and superchargers is their source of energy. Superchargers
can be powered mechanically by means of a belt or chain that is connected to
the engine’s crankshaft. Turbochargers use a turbine rotor that is powered by
the gases from the engine exhaust manifolds.

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The
turbocharger was developed in 1905 and began to be widely used in the mid
1960s. To make the turbocharger, two impellers were needed; one was a turbine wheel,
which was rotated by the exhaust gas. The second impeller was a compressor
impeller. The compressor impeller increased the pressure of the air. These were
fitted onto a center housing/hub rotating assembly. As explained above, the
turbocharger was able to generate a large power output from a compact engine. However,
it was found that the turbocharger experienced something called turbo lag. This
was essentially, a slight delay between the intention to accelerate and the
actual acceleration of the vehicle. As a result, ceramics were used for the turbine
rotor and this reduced the overall weight of the component as well as the
rotational inertia moment. Therefore, the turbo lag was reduced. In 1985, the
world’s first ceramic turbocharger was made and it incorporated silicon
nitride. Figure 1 shows a silicon nitride turbocharger and figure 2 shows the operation mechanism of the turbocharger. Silicon nitride was a
better material to use compared to the tradition nickel based super alloys. This
was due to silicon nitride ceramic having a much lower density compared to the
nickel based super alloys. The density of the silicon nitride ceramic was
approximately 3.2Mg/m3 and the density of the metallic alloy was
8.2Mg/m3. As you can see from figure 2, the revolution speeds for a
ceramic rotor and a metal rotor are compared. The time taken to reach 10,000rpm
is approximately 36% shorter for the ceramic rotor. As well as the silicon
nitride turbocharger being lightweight and having a low density, it also had a high thermal resistance, which was
important in order to resist degradation in the high temperature exhaust gas.