ENGINE
Chapter 12.
Performance,
Fuel consumption, Noise, Vibration
1. Required Performances
Various performances are required for the
engine. Each performance is related with each other in complex manner, so these
affect to the performance of the vehicle. Furthermore, as time is going, which
performance is more important has been changed. However, the output power is
the most important item because the purpose of the engine is developed making a
power for the vehicle. Conventionally, to operate engine for more work should
need more fuel to be used. Recently, by enhancing the engine efficiency, better
fuel efficiency and better output can be acquired.
To develop the combustion efficiency of the
engine is concerned to the purification of the exhaust gas. The carbon monoxide
and the hydrogen carbon among the three major harmful materials in the exhaust
gas may not be exist if the gasoline can be completely combusted, in ideal. The
one, the nitrogen oxide is also one of the important problems.
Considering that the engine weight is 10∼15% of whole weigh of the vehicle, another method for acquiring
better output and fuel efficiency at the same time is to make engine be compact
and light. With the same output, the power of vehicle having lighter engine
will be higher. The lighter and compact engine enhances the fuel consumption.
Also, to ensure the good steering, the vehicle should be light and the weigh
balance is distributed 50:50 at the front and the rear or similarly.
Engine also should have the features to be
driven by the driver’s willingness. For example, when the driver presses the
accelerator pedal, if the engine output is too high, then it is not so good for
the safety. The response, how to act according to the pressed amount of the
accelerator pedal, can make a big affect to the drive condition.
As the engine get the driving force by the
combustion of the fuel, the noise and vibration can not be avoided. It is
important to prevent these noises and vibrations from transmitting to the
passenger.
Additionally, as the engine is one mechanical
part of the vehicle, how to maintain the engine is also an important factors.
2. What is Output?
The engine is the device converting the heat
energy to the force. The basic performance is represented by the three major
factors such as the fuel consumption indicating how much gasoline is
combusted, the torque indicating how much force is generated thereby,
and the power indicating how much work is performed per unit time.
Among them, the fuel consumption is easy to
be notified because it is easily detected by measuring used fuel amount. Then,
what are the others, the power and the torque?
As we have explained frequently, the working
principle of the gasoline engine is that the expansion force by the combustion
of the gasoline is converted into the force pressing the piston to rotate the
crankshaft.
When ascending up to the inclined road, we
press the accelerator pedal to get high power. When running constantly in the
even road, we just press the accelerator a little. As connecting to the
throttle valve controlling the amount of intake air, the pressed depth of the
accelerator pedal directly affects to the open amount of the throttle valve.
The fuel injection amount is decided by the
amount of the intake air. When the air is inhaled with little amount by little
pressing the pedal, the gasoline injection amount will be small. When the air
amount is large by pressing deeply, then the fuel injection amount will be
increased.
That is, the ratio between the air amount and
the fuel amount is already preset, so the accelerator pedal controls only the
inhale air amount. So, pressing the pedal little, the mixture amount is small
and the power of engine, while pressing the pedal more, the power of engine
will be increased because the mixture amount is increased.
Generally, the engine performance is decided
by the engine force. The force is represented in unit of kg. In the vehicle, as
the ultimate force is the rotating force driving the wheel, it is prefer to
represent in unit of torque, i.e. kg·m, acquired by
multiple the magnitude of force with the distance between the center of rotate
to the force applying point.
In another aspect of engine performance, how
much work is possible within certain time period is also important. This work
amount is the power represented by horse power.
3. Representing Method for Power
Generally, the most important element of the
engine performance is the output (power). When a new engine is installed, some
one says “What horse power has it?” This horse power is the work efficiency,
that is, the unit indicating the work amount
during specific time period, so called the dynamic output (power).
This concept was suggested by the James Watts who invented the steam
engine in England. To compare the dynamic performances of the some kinds of the
steam engines, as the horse power used for water pumping works in the coal
mine, the one horse power is 550 ft·lbf/s. Converting into
the metric system, it will be 75 kg·m/s. This is the power
for pulling up the 75kg weight per 1m in one second.
For the unit of the Horsepower, it will be
represented HP in abbreviation, or the PS Pferdestarke from Germany. The PS is
more usually used. In SI unit system, representing with W (watt), 1 PS is about
735.4W. So, 100PS is 73.5kW, 100kW is 136PS.
In the vehicle catalogue, we can see
additional word such as (Net) or (Gross) in front of the unit of PS/rpm. As the
engine output is generally measured with being set the engine to the measuring equipment,
the measured output is changed according to the measuring condition, and there
is dispersion in measured values. Therefore, to indicate the output, Net value
and Gross value are used. The Gross value is measured value with engine only,
and the Net value is measured value with being set the engine to the vehicle.
For the gasoline engine, the Net value is 15% less than the Gross value. If
there is no notice, the larger value is the Gross one.
The power is the function of the time. The
engine power will be increased proportional to the rpm because the work amount
per time is increased when the rpm is higher. However, when the engine rpm is
increasing, the dynamic parts can not run over the certain value, or the engine
can not intake or exhaust faster than limit, or the engine power is excessively wasted for
driving engine itself if the rpm is over than
certain rpm. That is the engine power has certain limit value. This is
the maximum power output. In catalogue, it is indicated with the rpm thereat.
4. What is Torque?
The torque or the twisting force which is
applied to a rotational matter such as bolt, axis rod and wheel. It depends not
only on the applied force but also on the length of the lever arm upon which
the force acts. By definition, torque is equal to force multiplied by the leverage;
the length from the center of the rotor to the point which a force is applied.
In engine, the torque is equal to force of
which the piston going down force multiplied by the distance from the center of
crank pin to the center of crankshaft.
So, the magnitude of the torque of certain
engine is decided by the force of which the piston presses the Connecting rod,
that is, the combustion force. The performance graph of torque is representing
that which piston is pressing the crankshaft with how much force when the
engine is rotating at what rpm. As this force will be transmitted to the wheel
finally, the impulsive force of the vehicle is small if the engine torque is
small, the impulsive force of the vehicle is high if the engine torque is high.
The expansion (exploded) force is determined
by many elements, especially, by the amount of the inhaled air into the
cylinder. With plentiful of air, it is possible to get high power. Considering
the relationship between the inhaled air amount and the rpm of engine, when the
engine has low speed of rotation, the movement of piston is also slow and
inhaled air amount is low. When the engine has high speed of rotation, the
movement of the piston is fast and the inhaled air amount is high. However, if
the engine has too high speed, then the intake valve may close before the air
is not fully inhaled into the cylinder yet. In this case, the inhaled air
amountper stroke (volumetric efficiency) is decreased. Therefore, the engine
torque curve has the peak shape.
For example, compare the engine torque
between the 2500rpm pick engine and the 5000rpm pick engine. The former engine
has the best performance at the 2500rpm but not so good performance at the
5000rpm.
On the contrary, the 5000rpm pick engine has
a good performance at high speed but it has low performance at low speed. So,
the engine characteristics are different between above engines even though the
maximum torques are same.
5. To enhance Power
The engine power is a working amount during a
specific time. The engine power can be increased as high as the cylinder volume
high, the combustion force high and the rpm high.
The engine size is represented by the
displacement volume. The cylinder displacement volume is the exhausted gas
amount from certain cylinder during the piston moves from the BDC to TDC. The
total displacement volume is the sum of volume of all cylinders. The cylinder
displacement volume is calculated from multiple the cross sectional area by the
stroke of the cylinder. It is represented by unit of cc or ℓ.
When the total displacement volume is bigger,
the engine output will be also higher. To compare the engine performance, the PS/ℓ is used. The PS/ℓ means that how much
horsepower is generated per 1ℓ of displacement volume. For
the passenger car, generally, the more cylinder has higher value of PS/ℓ because volumetric efficiency is higher with multiple cylinder.
But the demerit of multiple cylinder is the much complicated structure and the
high cost.
The pressing force at the piston is
calculated by deviding a work amount per cycle by the displacement volume. By
this calculation, the pressing force at the piston is the pressure. But the
pressure at the piston is continuously changed by the position of piston and
the stroke. So, the the mean pressure per cycle is used for a calculation. This
is called as the mean effective pressure, the average pressure in the cylinder.
To enhance the engine power, the main three
elements including the total displacement volume, the mean effective pressure,
and the rpm should be enhanced. The work per certain time shall be increased by
enhancing the rpm. Deciding the total displacement volume of the engine, how
the mean effective pressure is increased and how the limitation of the rpm is
overcomed are the major focusing point for a developing of an engine to enhance
the engine power.
6. S/B
Ratio & Output
The displacement volume of cylinder is calculated
by the cross sectional area of cylinder and the stroke. Also the cross
sectional area is calculated by the daimeter of cylinder (Bore). So, the main
factors of displacement are the Bore and the Stroke. The bore and the stroke
may differ from each engine even though the same number of cylinder and the
same cylinder displacement. That is, some engine have the thin and long
cylinder, other engines have the fat and short cylinder. The ratio between the length
of stroke and diameter of bore is called Stroke/Bore ratio.
For the passenger car, the Stroke/Bore (S/B) ratio
is about 0.7∼1.3. The S/B ratio is less than 1, the stroke
is smaller than the bore, it is called Short Stroke. The S/B ratio is
higher than 1, the stroke is larger than bore, it is called Long Stroke.
The S/B ratio is just 1, the stroke is equal to the bore diameter, it is called
Square.
With the same displacement volume, the Short
Stroke engine has more potential to have higher power because larger bore
engine can make a larger valve diameter and can make a high engine rpm without
increasing the piston speed.
First of all, consider about the bore. The
gas amount will be larger as the valve diameter or the Valve Lift is larger. With
larger gas amount, it is possible to get higher output because more gasoline
will be combusted. Additionally, if the valve diameter will be larger, for the
same gas amount, the valve lift can be made smaller. So the valve movement will
be small at the high speed. However, the larger valve diameter has larger
diameter of inteke port, the large intake port engine can not make the fast
flow of intake gas at low speed so combustion may be degrade.
Next, considering about the piston speed. With
the same rpm of engine, the piston in long stroke should be move as fast as the
stroke length. The piston speed has a limitation. When the piston moves in high
speed, the lubricant oil may not be properly worked, or the piston inertia
force will be too high. The rpm of short stroke engine can be more increased
than the long stroke engine, if the engines has same limitation of piston
speed. Recently, the limite of the average piston speed is about 15∼22m per second.
In general, the engine for high speed and
output such as sports car shall accept Short Stroke or Square type S/B ratio,
the engine for commercial car accepts the Long Stroke to increase the torque instead of speed.
7. Compression Ratio & Output
In the previous section, the power can be
enhanced by increasing the intake air and increasing the engine rpm. Also there is one more method to
increase the engine power. That is the compression ratio.
When the piston is at the TDC, the space
which is surrounded by the piston and the cylinder head including the
intake-exhaust vlaves is the combustion chamber. The compression ratio is that
the cylinder volume is devided by compression chamber volume. The cylinder
volume is the total volume of compression chamber volume and the displacement
of cylinder.
The compression ratio represents how much the
intake mixture is compressed. The compression ratio in the vehicle catalogue is
a theoretical value by a calculation. In general, it is about 9 ∼
10 for normal gasoline engine and about 12 ∼ 13 and for
racing engine.
As the compression ratio is high, the mixture
is compresses strongly. So the mixture temperature will be high and the
combustion will be performed in short time. Then the combustion pressure will
be high and the torque and power will also be high. Furthermore, in the
combustion stroke, the expansion ratio is also high, so the exhaust gas has not
too high temperature. So the fuel efficiency will be good.
However, if the compression ratio is too high,
the engine can easily have abnormal combustion such as knocking. So it has
limitation. Knocking is related with mixture temperature, flow, chamber wall
temperature as well as the compression ratio. So, to increase the compression
ratio should be followed by the good cooling system for the cylinder head. Furthermore,
the engine should have higher strength for high compression ratio. The high
performance engine should be carefully designed.
There are theoretical compression ratio and
the actual compression ratio. The actual compression ratio indicates how much
the intake air is compressed actually. For example, in the intake stroke, if
the air is not inhaled sufficiently, then the actual compression ratio is less
than theoretical ratio. In the turbo
engine, if the boost pressure is 1atm, then the actual compression ratio will
be twice. So, the actual compression ratio is the important factors for the
enhancing the power. In above, the knocking is affected by the actual
compression ratio.
8. Increasing power by High rpm (rpm limit)
To make a high power engine, the fuel amount of
combustion is increased. Even the fuel amount is increased, if the air amount
is not increased, then it is no meaning. Therefore, to make a high power
engine, the intake air amount be more.
The air flow speed at the intake port is
divided the intake air quantity by the cross sectional area. The intake air
amount will be increased by the increasing of the engine rpm. So, the engine
output is proportion to the rpm.
The flow resistance of the air will be
increased as the air flow is fast. By enlarging the duct or volume of air
cleaner, the flow resistance can be reduced. However, the resistance around the
valve is not controlled. So, over the certain rpm, the power can not be increased
any more. Therefore, to get high output at the high speed, the intake air speed
should be decreased at the high speed. To do so, there are some methods to be
considered.
⑴ Increase the
number of cylinder: with the same total displacement volume, if the cylinder
number is increased, then the cylinder diameter will be reduced and then valve
diameter will do so. Therefore, the intake flow velocity will be reduced.
⑵ Increase the
number of intake valve: with the same reason mentioned in ⑴,
the air flow velocity will be reduced around the intake valve.
⑶ Enlarge the lift
of intake valve and elongate the opening time: The opening time of intake valve
is about 240° in terms of crankshaft rotation angle. In
the racing engine, it is about 280∼320°.
⑷ Design the SHORT
STROKE: with the same displacement volume, the SHORT STROKE is to make the
valve be enlarged. So, the opening area is also large and then the intake air
speed will be slow.
If the intake air speed is sufficiently slow,
the engine rpm can be increased more to make more power.
If the engine rpm is increased, the engine
should endure against the high rpm. That is, the engine should be strengthening
to ensure the high rpm. Generally, the engine should be lightened to reduce the
inertia force, and enhanced the strength of the body and parts of engine.
9. Transient Characteristic & Response
The engine makes large torque but
acceleration response is slow, the engine is not a high performance engine. The
acceleration performance or the response of the engine can be affected by the
weight of the car or gear ratio.
When the driving condition is changed, the intermediate
state between before and after is called transient or partial state. The engine
characteristic at partial state is called the transient characteristic of the
engine. The transient characteristic is basically related with the changing of
the rpm and the inertia force. The important things for the response are the
weight of the dynamic parts of the engine and the changing ability of the air/fuel while acceleration.
To reduce the inertia force of the dynamic
parts of the engine, the dynamic parts should be made as light as possible.
In the fuel injection type engine, an intake
collector (surge tank) has a similar volume with the total displacement volume.
When the accelerator is pressed to open the throttle valve, the air can not be
inhaled into the manifold immediately because of the inertia force of the air.
Therefore, the first movement of the engine
torque will be delay. To solve this problem, if the volume of the collector
(surge tank) is increased, then the engine output shall be increased.
In some fuel system, the gasoline may not be
flown smoothly because the gasoline sprayed from the injector. In this case,
when the throttle valve is open quickly, the mixture is leaned and then the
initial torque of the engine may be delayed. To solve this problem, there is a
method in which the injection amount is selectively increased at that moment.
10. Cylinder Array & Performance
There are three
method for arraying the cylinders, in-line type, V-type, and opposed type. What
relationship is there between the cylinder array and the engine performance?
The
in-line type engine has the cylinder in sequentially arrayed. There are from
2-cylinder type to 6-cylinder type. In the in-line type, the structure of the
cylinder block is very simple and the cylinder head is one body, so the engine
shall be light and compact. It is used widely from commercial car to racing
car.
In the in-line type engine, generally, the
cylinder number is 4 when the displacement volume is up to 2ℓ.
The cylinder number is 6 more than 2ℓ less than 3.5ℓ. The 4-cylinder engine having the displacement volume of from 1ℓto 1.5ℓ is used for commercial vehicle,
and one having more and up to 2ℓ is used for high
performance purposed car. Engine for the displacement volume of 2ℓ
is generally made into 4-cylinder or 6-cylinder. The 6-cylinder engine has
smaller combustion chamber and is easy to be made with SHORT STROKE. So it can
be get large maximum output.
The
in-line 6-cylinder engine has the long length so it needs somewhat
high cost. But, the size is compact in compare with the performance, and the
turbocharger can be easily attached. So it can be utilized in high performance
engine. Additionally, the inertia force of the piston-crank is well balanced so
it shows good features at the anti-vibration. However, it is hard to install
widely in the engine room of FF type vehicle; so generally, it is installed at
the FR type vehicle in longitudinal direction. The 3-cylinder or 5-cylinder is
rarely used in the in-line type.
By dividing 6-cylinder into two set of serial
3-cylinder and facing them to array in parallel, the length is reduced almost
half of the in-line 6-cylinder engine is the V-Type 6-cylinder engine. As this engine has the high
intake-exhaust efficiency because the bore diameter can be enlarged easily, it
is easy to get high power.
If the angle of V array is set to 60°, the feature is closed to the serial 6-cylinder engine. It can
be installed at the FF type vehicle. So it is possible for the FF car to be
developed into high performance car.
The
V-type engine generally consists of 6-cylinder. By combining the serial 4-cylinder
and the serial 6-cylinder, the V8 and the V12 engines can be manufactured
respectively. They are generally installed at the large vehicle or sports car. The
V6 engine is not easy to be utilized because the width of the engine is wider
and weight is heavier.
The
opposed engine is the same with the V-type engine having the 180°
of the angle. The center of engine will be lower than others.
11. Fuel Consumption Ratio
The fuel efficiency of the engine is
represented by the fuel consumption rate. The fuel consumption amount for the
driving is changed by the driving condition. When the dynamic performance is
measured by attaching to the dynamometer to compare with other engine, the
consumption amount of the fuel should be considered.
Therefore, the fuel consumption rate is
represented by fuel consumption amount per work, and the unit is g/PS·h. Assume that when a engine is rotating with 3000rpm at the
dynamometer, the engine outputs 55PS, and 11kg gasoline is used for 1 hour
working in this condition, then the fuel consumption rate is 220g/PS·h.
When referring to the graph of fuel
consumption rate in the engine performance curve, that the fuel consumption
rate is minimized with certain rpm of engine is more concerned than the fuel
amount. The actual fuel consumption rate shall be measured in actual driving
condition at the vehicle.
Generally to say, the catalogue indicates the
fuel consumption rate with the 10-15 mode rate and the 60km/h steady rate. On
here, the rate is just concerned to the engine itself.
To reduce the fuel consumption rate, the fuel
is used less as possible and the heat should be thoroughly converted into the
dynamic force. So, it is related with the heat efficiency. For example, the
mixture should be combusted with high temperature and high pressure, completely
and fast as possible. And the heat loss to the exhaust gas and to the cylinder
wall should be reduced as possible. As well as the mechanical friction should
be reduced also.
To calculate how the engine uses the heat
from the gasoline in classifying according to the element is the heat balance.
To indicate this heat balance with the graph
is the heat balance graph. Generally
to say about the heat balance of the gasoline engine. The heat for output, the
heat for loss in exhaust gas and the heat for loss through the cylinder wall
are 30% separately, and 10% is for others. Until now, the most heat efficiency
of the engine is about 35%, that is, in the term of fuel consumption rate,
about 170g/PS·h.
12. Output & Fuel Efficiency
As the air amount is increased to enhance the
engine output, the fuel amount will be increased, so the fuel efficiency is
degraded. However, if the mixture can be completely combusted to increase the
heat efficiency and to get higher output, then the high fuel efficiency as well
as the high output will be acquired. Additionally, the exhaust gas has less
harmful elements.
The engine heat efficiency is the ratio of
the heat capacity used for working. To increase the heat efficiency, the
expansion of the gas should be as large as possible, at the same time; the loss
energy should be as small as possible. The loss energies in the engine are the cooling loss by cooling system, the exhaust loss by being taken out with
the hot exhaust gas, and the intake-exhaust
loss (pumping loss) used for intake-exhaust operation.
To increase the heat efficiency by increasing
the expansion force of the combusted gas is related with to increase the
mixture amount and to increase the compression ratio.
To reduce the cooling loss, the temperature
of the combustion chamber should be increased. By changing the shape of
combustion chamber to enhance the compression ratio, the chamber temperature
will be increased at the compression stroke as well as the knocking is
prevented. In other hand, the method using the higher cooling water is also
concerned.
To reduce the intake-exhaust loss (pumping
loss), The intake-exhaust tube should be short and have less bent portion as
possible.
To enhance the air flow at the valve, the
diameter of the valve may be enlarged or the number of valve may be increased. However,
in that case, if the mixture flow is too slow, or if the structure of the
chamber is too complicated, then the heat efficiency will be degraded. Therefore,
it should be carefully designed.
One more, to enhance the heat efficiency, it should
be considered that the friction loss generated when the piston moves. The mechanical energy loss in driving the
auxiliary equipments should be reduced.
13. Fuel Efficiency of Vehicle
Even though the fuel consumption rate
indicates the engine fuel efficiency, this value is not the exact fuel
efficiency of vehicle. With the same engine, the fuel efficiency may differ
according that it is installed at heavy and large vehicle or it is installed at
light and small vehicle.
Comparing one case that a vehicle includes a
small engine having good fuel efficiency and another case that a vehicle includes
a large engine having bad fuel efficiency but high power, the actual fuel
efficiency will be changed by the driving condition. For example, if a car is
usually used in the low rpm condition, then the small displacement volume is
more effective. If the car is usually used in high speed or high power
condition, then the large displacement volume engine will be more effective.
For the comparing of the fuel efficiency
between engines, the specific test mode is required. The specific test mode
means that the test method and test conditions are specified. There are many
test mode which should be suggested in catalogue, the 10-15 mode running fuel
consumption, the 60km/h steady fuel consumption, FTP 75 mode and so on.
In representing the fuel consumption rate,
for engine only, the unit of g/PS-h is used, the unit of km/ℓ
indicating for vehicle what km the car can run with 1ℓ of
fuel is used.
The
10-15 mode fuel efficiency is acquired from dividing the running distance by
the amount of the used fuel, the vehicle is tested at the dynamometer according
to the predetermined pattern cycle of idling → start
acceleration → running with constant speed →
deceleration. In the past, the driving pattern had the maximum speed of 40km/h,
however, it was not proper to the modern trafic condition. Recently, the
maximum speed sets to 70km/h, the 15 mode is added to this test.
The 60km/h steady fuel efficiency is acquired from the used fuel amount when a
car is driving with constant speed of 60km/h with the gross weight having full
passengers and baggage at the paved plain road without wind. Generally, this
value is measured in the ideal state by the manufacturer to suggest to
government. The actual value is less than this value.
14. Vibration of Engine
There are many sources to make vibration in
engine. There are major three vibrations, one is from the combustion of the
engine, one another is from the inertia force of the reciprocal and rotational
movement at the dynamic system such as piston, connecting rod, crankshaft, and
others.
The vibration from the engine is as much as
high pressure of the combustion. And, the engine having high compression ratio
and high performance makes more noise. The vibration of the turbo engine makes
20~50% more noise than NA engine. In this case, some devices for preventing
from noise are used and the auxiliary devices are attached at the portions less
affected by vibration.
Additionally, by changing the engine mounting
position or adopting the vibration absorber with the mounting portions, the
vibration can not be transmitted to the body directly.
The inertia force is one major source of the
vibration. As the piston moves from the highest point to the lowest point with
various accelerations. The crankshaft makes a vibration waves and an inertia
force from the rotation of the crank pin. The Connecting rod makes an inertia
force from the combination of the reciprocal and rotational movement. In the
multi cylinder engine, the pistons are connected to the crankshaft, so each
inertia will be canceled each other. It is very complicated with the number of
cylinders, array of them and each timing of combustion. Therefore, using the
counter weight, the inertia force is balanced with the total weight. To match
the balance of the inertia force completely is very difficult.
The inertia force is less when the dynamic parts
such as piston and Connecting rod have lighter weight. With the same
displacement volume, the engine having more number of cylinders has less
inertia force because the parts are small and light. When the inertia force is
small, the possibility to make a vibration will be few and it will rotate at
high speed with the same strength.
By lightening the weight of dynamic part, the
inertia force at each part will be small. With the same rpm, the strength of
these parts will not be maintained highly. Generally, the device having lower
strength is lighter than the device having higher strength. To be lightening is
most important point to increase performance as well as to prevent vibration.
15. Noise of Engine
The noises from the engine are the combustion
noise and mechanical sounds. The mechanical sounds is caused by the friction
between the parts. When the engine rotates with high speed, the noise will be
changed and be louder. When a driver changes the shift to up or down,
generally, the driver may selects the proper gear by engine noise. So, the
sound of engine helps the driver for the driving. Therefore, the engine sound
should be noticed but it shall not the noise but the sound.
The mechanical noise is made from the
vibration of the cylinder and cylinder head by the combustion force. When the
mixture amount is increased or the combustion pressure is higher, then the
noise will be louder. Someone may feel that the turbo engine make less noise
than the NA engine. The reasons are the turbine absorbs the exhaust energy and
the variation of the combustion pressure is smaller.
The mechanical sounds comes from the friction
and bump the dynamic parts such as gear, chain, and valves. For example, the
cam hits the valve lifter, rocker arm and camshaft hits the valves, the valve
bumps with the valve seat and so on.
The resonance noise from the vibration is
louder than the direct mechanicla noise. So, the causes of the noise from the
engine can not be exactly found. Any way, that there is a noise is not good
situation because some parts of the engine shall be hit with others and this is
bad for the endurance of parts. If you detect abnormal noise, please check the
system as soon as possible.
Comparing the combustion noise with the
mechanical noise, at the low speed, the combustion noise is larger. When the
rpm is over 3000rpm, the inertial force is larger and the mechanical noise will
be larger.
The noise from the engine room will be
protected by attaching absorbing materials under the hood and in front of the
dashboard, the boundary of the engine room and cabin. The noise absorbing
materials are glass wool, felt and so on.
