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Four Stroke Engine
The four stroke engine was first demonstrated by Nikolaus Otto in 18761, hence it is also known as the Otto cycle. The technically correct term is actually four stroke cycle. The four stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks.
Speed 10 fps
The four strokes of the cycle are intake, compression, power, and exhaust. Each corresponds to one full stroke of the piston; therefore, the complete cycle requires two revolutions of the crankshaft to complete.
During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).
As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture.
At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.
At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.
This animation also illustrates a simple ignition system using breaker points, coil, condenser, and battery.
A number of visitors have written to point out a problem with the breaker points in my illustration. In this style ignition circuit, the spark plug will fire just as the breaker points open. The illustration appears to have this backwards.
In fact, the illustration is correct; it just moves so fast it’s difficult to see! Here’s a close-up of the frames just at the point the plug fires:
My original intent was to accurately show that the points need to remain closed for only a fraction of a second, called the dwell. By
illustrating this, I inadvertently obscured the overall operation of the circuit. Perhaps someday I’ll prepare a more detailed illustration of the ignition system alone.
Larger four stroke engines usually include more than one cylinder, have various arrangements for the camshaft (dual, overhead, etc.), sometimes feature fuel injection, turbochargers, multiple valves, etc. None of these enhancements changes the basic operation of the engine.
The power for vehicle propulsion is supplied by the internal combustion engine. This engine is divided into three main parts:
Robusta headpiece containing a combustion chamber for each cylinder; within each are the intake valves, through which reaches the air-fuel mixture to the pistons, and the exhaust, where they exit gases from combustion cycle conducted once. The stock wire leads to accommodate spark plugs that cause electrical spark.
centerpiece engine where the cylinder cooling chamber, crankshaft, camshaft, is the core engine.
bottom of the engine used as an oil reservoir.
Operating principle of the 4-stroke engine
When the explosion of the air-fuel mixture caused by the spark of the spark plug occurs, the expanding gases violently pushes the piston downward, which receives the crankshaft transmits it to the drive wheels.
1. Admission: The piston descends from its highest position to a lowest point, while the intake valve is open and the compression remains closed.
2. Compression: With both valves closed the piston moves up, pushing the air mass and gas, reaching a maximum value of compression.
3. Explosion: At time ending the compression stroke, inflammation of the mixture is produced by a spark from the spark plug in. Inflammation of the mixture produces a violent explosion, this sharp increase in pressure causes the piston to be pushed down violently.
4. Escape: After the explosion stroke, the piston starts again rise, when the exhaust valve through which open are ejected from the combustion gases, beginning a new cycle.
The crank shaft has rotated two turns cycling work Valves open and close according to rotation of the cam shaft
Turning the wheel in either direction, bar transcends the movement to a gearbox and by a short arm transmits motion to the address bar to move the drive wheels.
The movement of the motor is transmitted to the rotatably gearbox, these elements engage and disengage by means of the clutch system. The gearbox is transmitted through shafts (constant velocity joint), front- or cardan shaft (rear wheel drive). The final drive is to move rotatably the driving wheels.
Mechanical engineering Introduction
Mechanical engineering is the discipline that applies the principles of engineering, physics, and material science for the design, analysis, manufacturing ,and maintenance of mechanical systems.
It is the branch of engineering that involves the design, production, and operation of machinery.
It is one of the oldest and broadest of the engineering diciplines.
Simple Definition of mechanical engineering
a type of engineering that is mainly concerned with the use of machines in industry.
Mechanical engineering Definition
a branch of engineering concerned primarily with the industrial application of mechanics and with the production of tools, machinery, and their products.
What Mechanical Engineers Do
Mechanical engineering is one of the broadest engineering disciplines. Mechanical engineers research, design, develop, build, and test mechanical and thermal sensors and devices, including tools, engines, and machines.
Duties of Mechanical Engineers
Analyze problems to see how mechanical and thermal devices might help solve a particular problem
Design or redesign mechanical and thermal devices or subsystems, using analysis and computer-aided design
Develop and test prototypes of devices they design
Analyze the test results and change the design or system as needed
Oversee the manufacturing process for the device
Important Qualities of Mechanical Engineers
Mechanical engineers design and build complex pieces of equipment and machinery. A creative mind is essential for this kind of work.
Mechanical engineers often work on projects with others, such as architects and computer scientists. They must listen to and analyze different approaches made by other experts to complete the task at hand.
Math skills :
Mechanical engineers use the principles of calculus, statistics, and other advanced subjects in math for analysis, design, and troubleshooting in their work.
Mechanical skills :
Mechanical skills allow engineers to apply basic engineering concepts and mechanical processes to the design of new devices and systems.
Mechanical engineers need good problem-solving skills to take scientific discoveries and use them to design and build useful products.
Condition Monitoring of Installations and Machinery
Condition Monitoring of Installations and Machinery
Improve the maintenance of your machinery and installations with our condition monitoring
A key prerequisite for the operation of efficient and profitable installations is the availability of machinery and components. With our condition monitoring you keep a watchful eye on the condition of your installation. Our experts at TÜV Rheinland ISTec GmbH identify each critical condition change and development of your machinery with the assistance of time and frequency-based (online) diagnostic procedures. By directly responding to excessive stress or wear, effective counteractive measures can be taken immediately. In doing so, the profitable operation of your installations and machinery is ensured. High repair costs and unwanted downtime are also thereby avoided.
Our employees are experts in the field of diagnostics and security tech-nology in various industrial sectors. With our condition monitoring systems for manufacturing, we are the right partner for you.
Would you like to learn how to utilize condition monitoring at your plant? Then contact one of our experts today.
Maximize the operational lifetime of your installation with our condition monitoring
With the condition monitoring of your installations and machinery, you are able to develop a long-term maintenance strategy. Vulnerability analyses and analyses of machine data, allow you to plan maintenance and inspections strategically and effectively. The operational lifetime of technical components is thereby fully utilized and you are able to reduce costs and increase the efficiency of your industrial installation. In addition, you benefit from the high diagnostic depth and analysis reliability of our system, as well as advanced warning time. As a result, you can meet growing demands on your machinery and installations in these times of industry 4.0.
Our systems for condition monitoring
Our experts assist you with the selection of the appropriate data collection technology and implementation in your industrial facility as well as continuous system support.
We have the following diagnostic systems:
Vibration diagnostic system tf COMOS:
Monitoring machinery with constant or variable speed or with frequency monitoring of passive components; from signal processing to amplitudes and phases of rotation-frequency proportions
Field of application: turbine generators, reactor coolant and circulation pumps, feed water pumps, compressors, key components in the food industry, machines for the printing industry
Acoustic monitoring system ta COMOS:
Automatic assistance and monitoring system for the monitoring of sound signals – from airborne to structure-borne sound signals; monitoring of the peak values as well as analyzing signals on a frequency-selective basis
Field of application: acoustic detection of changes in the environment signals from machine groups, leakage noise from boilers or pipes; acoustic detection of glass breakage in unmanned industrial complexes
Our services for your installation and machinery include:
Analysis of vibrations in mechanical behavior
Early detection of damaged parts
Sound location method
Cyclical data collection at fixed intervals
Our many years of experience in machine diagnostics for the condition monitoring of your systems
With our in-house vibration diagnostic system, you have at your disposal an instrument that combines the requirements of a typical condition monitoring system and structure health monitoring system, therefore, supporting higher availability for your machinery. These measures in combination with our acoustic monitoring system and the help of acoustic detection, can assess the status of the complete installation. Through our many years of experience in the field of machine diagnostics, we are the right partner for condition monitoring systems.
Request an offer for the condition monitoring of your industrial facility today!
Machine fault diagnosis is a field of mechanical engineering concerned with finding faults arising in machines. A particularly well developed part of it applies specifically to rotating machinery, one of the most common types encountered. To identify the most probable faults leading to failure, many methods are used for data collection, including vibration monitoring, thermal imaging, oil particle analysis, etc. Then these data are processed utilizing methods like spectral analysis, wavelet analysis, wavelet transform, short term Fourier transform, Gabor Expansion, Wigner-Ville distribution (WVD), cepstrum, bispectrum, correlation method, high resolution spectral analysis, waveform analysis (in the time domain, because spectral analysis usually concerns only frequency distribution and not phase information) and others. The results of this analysis are used in a root cause failure analysis in order to determine the original cause of the fault. For example, if a bearing fault is diagnosed, then it is likely that the bearing was not itself damaged at installation, but rather as the consequence of another installation error (e.g., misalignment) which then led to bearing damage. Diagnosing the bearing’s damaged state is not enough for precision maintenance purposes. The root cause needs to be identified and remedied. If this is not done, the replacement bearing will soon wear out for the same reason and the machine will suffer more damage, remaining dangerous. Of course, the cause may also be visible as a result of the spectral analysis undertaken at the data-collection stage, but this may not always be the case.
The most common technique for detecting faults is the time-frequency analysis technique. For a rotating machine, the rotational speed of the machine (often known as the RPM), is not a constant, especially not during the start-up and shutdown stages of the machine. Even if the machine is running in the steady state, the rotational speed will vary around a steady-state mean value, and this variation depends on load and other factors. Since sound and vibration signals obtained from a rotating machine which are strongly related to its rotational speed, it can be said that they are time-variant signals in nature. These time-variant features carry the machine fault signatures. Consequently, how these features are extracted and interpreted is important to research and industrial applications.
The most common method used in signal analysis is the FFT, or Fourier transform. The Fourier transform and its inverse counterpart offer two perspectives to study a signal: via the time domain or via the frequency domain. The FFT-based spectrum of a time signal shows us the existence of its frequency contents. By studying these and their magnitude or phase relations, we can obtain various types of information, such as harmonics, sidebands, beat frequency, bearing fault frequency and so on. However, the FFT is only suitable for signals whose frequency contents do not change over time; however, as mentioned above, the frequency contents of the sound and vibration signals obtained from a rotating machine are very much time-dependent. For this reason, FFT-based spectra are unable to detect how the frequency contents develop over time. To be more specific, if the RPM of a machine is increasing or decreasing during its startup or shutdown period, its bandwidth in the FFT spectrum will become much wider than it would be simply for the steady state. Hence, in such a case, the harmonics are not so distinguishable in the spectrum.
The time frequency approach for machine fault diagnosis can be divided into two broad categories: linear methods and the quadratic methods. The difference is that linear transforms can be inverted to construct the time signal, thus, they are more suitable for signal processing, such as noise reduction and time-varying filtering. Although the quadratic method describes the energy distribution of a signal in the joint time frequency domain, which is useful for analysis, classification, and detection of signal features, phase information is lost in the quadratic time-frequency representation; also, the time histories cannot be reconstructed with this method.
The short-term Fourier transform (STFT) and the Gabor transform are two algorithms commonly used as linear time-frequency methods. If we consider linear time-frequency analysis to be the evolution of the conventional FFT, then quadratic time frequency analysis would be the power spectrum counterpart. Quadratic algorithms include the Gabor spectrogram, Cohen’s class and the adaptive spectrogram. The main advantage of time frequency analysis is discovering the patterns of frequency changes, which usually represent the nature of the signal. As long as this pattern is identified the machine fault associated with this pattern can be identified. Another important use of time frequency analysis is the ability to filter out a particular frequency component using a time-varying filter.
Schemes of applying diagnostics Edit
Fault diagnostics in usual industrial practice need to be applied according to guidelines. This need arises from the fact that diagnostics on their own may be capable of saving a single machine if monitoring is adequate, but it is impossible to apply them to all the equipment. The investment needed to either install continuous condition monitoring sensors on all the machinery in a factory or to check enough samples from all machinery on a regular basis would be prohibitive.
As a result, using fault diagnostics to meet industrial needs in a cost-effective way, and to reduce maintenance costs without requiring more investments than the cost of what is to be avoided in the first place, requires an effective scheme of applying them. This is the subject of maintenance, repair and operations; the different strategies include:
Planned preventative maintenance
Corrective maintenance (does not use diagnostics)
Integrated vehicle health management
See also Edit
Spread-spectrum time-domain reflectometry
Fuel injection, system in an internal-combustion engine that delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel’s greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders. A diesel fuel injector sprays an intermittent, timed, metered quantity of fuel into a cylinder, distributing the fuel throughout the air within. Fuel injection is also now used in gasoline engines in place of a carburetor. In gasoline engines the fuel usually is injected into the intake manifold and mixed with air, and the resulting mixture is delivered to the cylinder. Modern fuel injection systems use computers to regulate the process. Fuel injection results in more efficient fuel combustion, improving fuel economy and engine performance and reducing polluting exhaust emissions.
By Ally Shigereka Julius
The function of the fuel system is to store and supply fuel to the cylinder chamberwhere it can be mixed with air, vaporized, and burned to produce energy. The fuel, whichcan be either gasoline or diesel is storedin a fuel tank. A fuel pump draws the fuel from the tank through fuel lines and delivers itthrough a fuel filter to either a carburetor or fuel injector,then delivered to the cylinder chamber for combustion.
Gasoline is a complex blend of carbon and hydrogen compounds. Additives are then addedto improve performance. All gasoline is basically the same, but no two blends areidentical. The two most important features of gasoline are volatility and resistance toknock (octane). Volatility is a measurement of how easily the fuel vaporizes. If thegasoline does not vaporize completely, it will not burn properly (liquid fuel will notburn).
If the gasoline vaporizes too easily the mixture will be too lean to burn properly.Since high temperatures increase volatility, it is desirable to have a low volatility fuelfor warm temperatures and a high volatility fuel for cold weather. The blends will bedifferent for summer and winter fuels. Vapor lock which was a persistent problem yearsago, exists very rarely today. In today’s cars the fuel is constantly circulating from thetank, through the system and back to the tank. The fuel does not stay still long enough toget so hot that it begins to vaporize. Resistance to knock or octane is simply thetemperature the gas will burn at. Higher octane fuel requires a higher temperature toburn. As compression ratio or pressure increases so does the need for higher octane fuel.Most engines today are low compression engines therefore requiring a lower octane fuel(87). Any higher octane than required is just wasting money. Other factors that affect theoctane requirements of the engine are: air/fuel ratio, ignition timing, enginetemperature, and carbon build up in the cylinder. Many automobile manufacturers haveinstalled exhaust gas recirculation systems to reduce cylinder chamber temperature. Ifthese systems are not working properly, the car will have a tendency to knock. Beforeswitching to a higher octane fuel to reduce knock, make sure to have these other causeschecked.
Diesel fuel, like gasoline is a complex blend of carbon and hydrogen compounds. It toorequires additives for maximum performance. There are two grades of diesel fuel used inautomobiles today: 1-D and 2-D. Number 2 diesel fuel has a lower volatility and is blendedfor higher loads and steady speeds, therefore works best in large truck applications.Because number 2 diesel fuel is less volatile, it tends to create hard starting in coldweather. On the other hand number 1 diesel is more volatile, and therefore more suitablefor use in an automobile, where there is constant changes in load and speed. Since dieselfuel vaporizes at a much higher temperature than gasoline, there is no need for a fuelevaporation control system as with gasoline. Diesel fuels are rated with a cetane numberrather than an octane number. While a higher octane of gasoline indicates resistance toignition, the higher cetane rating of diesel fuel indicates the ease at which the fuelwill ignite. Most number 1 diesel fuels have a cetane rating of 50, while number 2 dieselfuel have a rating of 45. Diesel fuel emissions are higher in sulfur, and lower in carbonmonoxide and hydrocarbons than gasoline and are subject to different emission testingstandards.
Tank location and design are always a compromise with available space. Most automobileshave a single tank located in the rear of the vehicle. Fuel tanks today have internalbaffles to prevent the fuel from sloshing back and forth. If you hear noises from the rearon acceleration and deceleration the baffles could be broken. All tanks have a fuel fillerpipe, a fuel outlet line to the engine and a vent system. All catalytic converter cars areequipped with a filler pipe restrictor so that leaded fuel, which is dispensed from athicker nozzle, cannot be introduced into the fuel system. All fuel tanks must be vented.Before 1970, fuel tanks were vented to the atmosphere, emitting hydrocarbon emissions.Since 1970 all tanks are vented through a charcoal canister, into the engine to be burnedbefore being released to the atmosphere. This is called evaporative emission control andwill be discussed further in the emission control section. Federal law requires that all1976 and newer cars have vehicle rollover protection devices to prevent fuel spills.
Steel lines and flexible hoses carry the fuel from the tank to the engine. Whenservicing or replacing the steel lines, copper or aluminum must never be used. Steel linesmust be replaced with steel. When replacing flexible rubber hoses, proper hose must beused. Ordinary rubber such as used in vacuum or water hose will soften and deteriorate. Becareful to route all hoses away from the exhaust system.
Two types of fuel pumps are used in automobiles; mechanical and electric. All fuelinjected cars today use electric fuel pumps, while most carbureted cars use mechanicalfuel pumps. Mechanical fuel pumps are diaphragm pumps, mounted on the engine and operatedby an eccentric cam usually on the camshaft. A rocker arm attached to the eccentric movesup and down flexing the diaphragm and pumping the fuel to the engine. Because electricpumps do not depend on an eccentric for operation, they can be located anywhere on thevehicle. In fact they work best when located near the fuel tank.
Many cars today, locate the fuel pump inside the fuel tank. While mechanical pumpsoperate on pressures of 4-6 psi (pounds per square inch), electric pumps can operate onpressures of 30-40 psi. Current is supplied to the pump immediately when the key isturned. This allows for constant pressure on the system for immediate starting. Electricfuel pumps can be either low pressure or high pressure. These pumps look identical, so becareful when replacing a fuel pump that the proper one is used. Fuel pumps are rated bypressure and volume. When checking fuel pump operation, both specifications must bechecked and met.
The fuel filter is the key to a properly functioning fuel delivery system. This is moretrue with fuel injection than with carbureted cars. Fuel injectors are more susceptible todamage from dirt because of their close tolerances, but also fuel injected cars useelectric fuel pumps. When the filter clogs, the electric fuel pump works so hard to pushpast the filter, that it burns itself up. Most cars use two filters. One inside the gastank and one in a line to the fuel injectors or carburetor. Unless some severe and unusualcondition occurs to cause a large amount of dirt to enter the gas tank, it is onlynecessary to replace the filter in the line.
ASE A4 Steering Suspension Practice Test
1. A vehicle has a steady pull to the left. All of these will cause this condition EXCEPT:
A. The caster angle.
B. Low tire pressure.
C. The camber angle.
D. Steering U-joint coupling.
2. Technician A says a vehicle will pull to the side with the most positive camber. Technician B says that too much negative camber will result in excessive wear on the inside tread of the tire. Who is correct?
A. Technician A
B. Technician B
C. Both A and B
D. Neither A or B
3. Two technicians are discussing inner and outer tie rods. Technician A says to turn the outer tie rod end to adjust the toe. Technician B says loose inner tie rod ends will cause a tire to feather. Who is correct?
A. Technician A
B. Technician B
C. Both A and B
D. Neither A or B
4. The rear tires on a vehicle with independent rear suspension are worn on the inside tread. Which of the following is MOST likely the cause of this condition?
A. The toe.
B. Underinflated tires.
C. The caster.
D. None of the above.
5. Technician A says SAI or Steering Angle Inclination is adjusted by changing the caster angle. Technician B says camber adjustments are included in the Included Angle. Who is correct?
A. Technician A
B. Technician B
C. Both A and B
D. Neither A or B