ENGINE Chapter 12. Performance, Fuel consumption, Noise, Vibration

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.