Plenum the engine. The design of the plenum itself

Plenum is one of the major part in intake
manifold. Plenum is the area between the throttle body – if the car is equipped
with a single throttle body, and the individual feeding paths called intake
runners which lead to each cylinder of the engine. Plenum is where the outside
air from the throttle body is stored before it flows into the intake runners.
Plenum comes with different sizes and volumes depend on the engine. The design
of the plenum itself can give different effects on the engine performance 5. The criteria need to be considered resistance of air
flow and good distribution of the air into the runners 6.

 

One of the parameters that can be consider
when designing plenum is the volume. The performance of an engine can be
affected by the volume of the plenum. Based on the study conducted by Ceviz and
Akin, the variation of plenum volume causes an improvement on the engine
performance characteristic 7. By doing the optimization on the plenum volume, the
maximum advantages of the engine performance in term of brake power can be
obtained 4, 7, 8.
On different engine speeds, different volumes are needed to suit the flow of
the intake charge air. By having variable plenum volume, the maximum power of
the engine can be achieved both in low and high engine speed. At low engine
speed, larger volume is more suitable, but as the engine speed increases, the
volume need to be decreased in order to achieve maximum power 7-9.

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According to a research conducted by Ceviz
in 2006, the volume of plenum plays an important role on the engine
performance. In the real world, because of the difficulties to implement a
continuously variable plenum volume, the design often used two intake manifold
with different volume 8. Ceviz conducted an experiment which the engine is
ran on a dynamometer. The engine used for this experiment is a 4 stroke engine
with bore and stroke of 86.4mm and 67.4mm respectively. The compression ratio
is 9.2 with the maximum power is 62kW at 5800rpm. The setup of the experiment
is as shown in Figure
2.1.

The first experiment is ran using
the original plenum without any additional volume and the data is recorded.
After the engine reached a steady state, the second and third experiment is
conducted and the different plenum volume is implemented by adding extra volume
at the back of the original plenum as shown in Figure. The additional volume
for the two experiment were 90cm3 and 180cm3
respectively. The findings from the experiment shows that the plenum volume can
affect the engine performance in term of brake power as well as fuel
consumption.

 

Figure
2.2: The torque
curve of three plenum volume condition 8.

 

 

Based
on , the result obtained shows that at low engine speed, the relationship of
brake power and brake torque is proportional to engine speed. The plenum volume
need to be increased when running on low speed 8.

 

Ceviz
conducted a similar experiment in 2010 but uses different engine with higher
engine speed range. The engine used in this experiment is Ford MVH-418, 4
cylinder fuel injected with bore of 80.6mm, stroke of 88mm and 10.1 compression
ratio. The engine have maximum power of 93kW at 6250rpm and maximum torque of
157Nm at 4500rpm. The engine is ran at ¾ of full load. The experiment uses
additional plenum volume of 40cm3 and 80cm3. The results
of the experiment is shown in Figure 2.3.

 

 

Figure 2.3: The result
of brake power vs engine speed with different plenum volume 7.

.

 

According
to Figure 2.3, as the engine speed increases, the
additional plenum volumes have no significant in the engine torque. At low
engine speed, between 1000-2000rpm, greater volume give better torque and
power, but as the speed increases, the power and torque is slightly the same as
there is no addition applied. Therefore, it can be conlcude that bigger volume
is suitable at low engine speed, but as the engine speed increases, the plenum
volume should be decreased 4, 6-9. 

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