Modern Engineering Thermodynamics

13.22 Modern Prime Mover Developments 517
Ceramic
bearings
Fuel
injector
Ceramic
valve
Ceramic
piston
Ceramic
head liner
Thermal
barrier
Ceramic
bearings
FIGURE 13.55
Typical ceramic components of a modern IC engine.
Current internal combustion engines are not only uninsulated, they are intentionally cooled. This is done to
prevent the buildup of excessively high internal temperatures that in turn would cause material failure due to
loss of strength. Consequently, about 80% of the chemical energy originally contained in the fuel leaves an IC
engine as thermal energy in the coolant and exhaust gases.
The development of high-temperature, high-strength ceramic or superalloy engine components is a step in the
direction of creating a truly adiabatic IC engine. In addition to reducing engine heat loss, these new components
allow higher internal operating temperatures to be achieved, and this in turn increases the maximum theoretical
thermal efficiency of the engine. For example, doubling the operating temperature from 2000°F (1093°C) to
4000°F (2204°C) increases the Carnot isentropic efficiency by about 10%. Figure 13.55 illustrates some of the
current uses of ceramics in reciprocating IC engines. Similar advances are being made in gas turbine engine
technology.
Other thermal efficiency–increasing technology, such as supercharging, turbocharging, and turbocompounding,
can be used to extract some of the thermal energy from the engine’s exhaust gases (see Figure 13.56). However,
it must be remembered that all cyclic heat engines (including all IC engines when their cycle is closed by
the environment) must have a heat loss rate to the environment, dictated by the second law of thermodynamics,
of
j _Qj loss ≥ T environment /T engine max
j _Q j fuel