physics, mechanical energy describes the potential energy and kinetic energy present in the components of a mechanical system. The mechanical energy of a body is that part of its total energy which is subject to change by mechanical work. It includes kinetic energy and potential energy. Some notable forms of energy that it does not include are thermal energy (which can be increased by frictional work, but not easily decreased) and rest energy (which is constant so long as the rest mass remains the same).
What is it?
The study of mechanics concerns the motion of physical bodies and the forces that act upon them. Most people are familiar with systems described by Newtonian mechanics - objects that sit around, move, collide, and are influenced by gravity. Mechanical energy includes things like the kinetic energy of a moving billiard ball, or the potential energy a roller coaster at the top of its track.
The physics of electromagnetism were not understood at the time of Newton, but in some situations, the mechanics (i.e. the mathematics of motion) of bodies influenced by electromagnetic forces is the same as that of those influenced by gravity. For example, two particles of opposite electrical charge experience an attractive force which is (allowing for certain idealizations) mathematically identical to the gravitational forces two passing planets experience. An electromechanical system might also involve the conversion of mechanical energy into electrical charges or magnetic fields, or vice versa.
Everyday objects are composed of atoms and molecules, which to some degree, are like billiard balls that are constantly bouncing off one another. "Mechanical energy" might include the kinetic energy of these particles, or potential energy stored in the physical arrangement. For example, a compressed solid exerts pressure because electromagnetic forces between particles tend to push them apart. Compressing a solid (moving the particles "uphill" against repulsive electromagnetic forces) stores potential energy in a similar way that pushing a boulder up a hill does (moving the object uphill against the attractive gravitational force of the Earth). On the other hand, a compressed gas exerts pressure because independently moving particles collide with the walls of the container and change direction. The particle is accelerated (its velocity vector changed), and the acceleration times the mass of the particle gives the force applied. Compressing a gas changes the average kinetic energy of the particles, which is reflected in the corresponding increase in the temperature of the gas. The pressure also increases, but this is because the same number of particles have been forced into a smaller volume, so they collide more often with the walls. The force of any given collision is the same, but the number of collisions has increased.
Potential energy does play a role in the pressure of a gas. During an individual collision, a gas molecule comes closer to the molecules of the container wall. The electric fields exert a force on the molecule, slowing it down and reducing its kinetic energy. This energy is temporarily stored as potential energy. Soon, the particle is nearly stationary (if it happened to approach head on), or at least, it is not approaching the wall any more. The electric fields continue to exert a force on the gas molecule. The force continues to change the velocity, and soon the molecule is moving away from the wall and gaining kinetic energy. Generally, the collision is elastic, and all of the kinetic energy is recovered and the particle continues moving with the same speed it had originally.
Solid mechanics studies how rigid bodies behave in response to external forces. Fluid mechanics studies the internal motion of liquids, gases, and other forms of matter. Mechanical energy can be expended in crushing a soda can, affecting the motion and positional arrangement of its component molecules. Mechanical energy can be transferred from the molecules of a solid to the molecules of a liquid when, for example, a glass of water is stirred.
Associated concepts
When a given quantity of mechanical energy is transferred (such as when throwing a ball, lifting a box, crushing a can, or stirring a beverage) it is said that this amount mechanical work has been done. Both mechanical energy and mechanical work are measured in the same units as energy in general. It is usually said that a component of a system has a certain amount of "mechanical energy" (i.e. it is a state function), whereas "mechanical work" describes the amount of mechanical energy a component has gained or lost.
The conservation of mechanical energy is a principle which states that, under certain conditions, the total mechanical energy of a system is constant. This rule does not hold when mechanical energy is converted to other forms, such as chemical, nuclear, or electromagnetic. However, the principle of general conservation of energy is so far an unbroken rule of physics - as far as we know, energy cannot be created or destroyed, only changed in form.
Simplifying assumptions
Scientists often make simplifying assumptions to make calculations about how mechanical systems behave. For example, instead of calculating the mechanical energy separately for each of the billions of molecules in a soccer ball, it is easier to treat the entire ball as one object. This means that only two numbers (one for kinetic mechanical energy, and one for potential mechanical energy) are needed for each dimension (for example, up/down, north/south, east/west) under consideration.
To calculate the energy of a system without any simplifying assumptions would require examining the state of all elementary particles and considering all four fundamental interactions. This is usually only done for very small systems, such as those studied in particle physics.
Distinguished from other types of energy
The classification of energy into different "types" often follows the boundaries of the fields of study in the natural sciences.
Chemical energy, the kind of potential energy stored in chemical bonds; studied in chemistry
Nuclear energy, energy stored in interactions between the particles in the atomic nucleus; studied in nuclear physics
Electromagnetic energy, in the form of electric charges, magnetic fields, and photons; from the study of electromagnetism
Various forms of energy in quantum mechanics; for example, the energy levels of electrons in an atom
In certain cases, it can be unclear what counts as "mechancial" energy. For example, is the energy stored in the structure of a crystal "mechanical" or "chemical"? Scientists generally use these "types" as convenient labels which clearly distinguish between different phenomena. It is not scientifically important to decide what is "mechanical" energy and what is "chemical". In these cases, usually there is a more specific name for the phenomenon in question. For example, in considering two bonded atoms, there are energy components from vibrational motion, from angular motions, from the electrical charge on the nuclei, secondary electromagnetic considerations like the Van der Waals force, and quantum mechanical contributions concerning the energy state of the electron shells.
Sunday, January 4, 2009
Gas Burners
Gas burners can fuel warm-air, hot water, or steam heating systems. When the thermostat in the system calls for heat, the burner's automatic gas valve opens, allowing gas to flow into a manifold and then into venturi tubes where it mixes with air. When the air-gas mixture emerges from the burner ports, the pilot ignites it and heat is created. A thermocouple adjacent to the pilot closes the gas valve if the pilot isn't working.
Solving Pilot Problems
Pilots in gas burners may be electric or gas. For problems with electric pilots, call in a professional. Gas pilots can be relit and cleaned by the homeowner.
Lighting a Gas Pilot
Before you try to relight a pilot that has gone out, read the instructions usually printed on the front of the boiler or furnace. If there are none, have your utility company light it or follow these steps:
Use the manual control knob on the automatic gas valve to turn off the gas to the main burner and pilot.
Allow at least 5 minutes for accumulated gas to dissipate before proceeding.
Use extreme caution, and take more time if your fuel is bottled gas -- it doesn't dissipate readily.
When the gas has dissipated, set the thermostat well below room temperature.
Turn the manual control knob to PILOT and light the pilot, holding the knob there for a minute.
Release the knob and turn it to ON.
If the pilot doesn't stay on, call the gas company. (Remember to reset the thermostat when the pilot's relit).
Adjusting the Pilot Flame
The pilot flame should be blue and should cover the thermocouple. Before adjusting the flame, turn the thermostat down. Reset it when you're finished with the adjustment.
Cleaning The Pilot Orifice
If you have trouble lighting the pilot, the orifice may be plugged. To clean it:
Shut off the gas supply by turning the gas inlet valve handle so it's at a right angle to the pipe.
Disconnect the thermocouple tub and the pilot gas line from the automatic gas valve.
Remove the bracket holding the pilot and the thermocouple.
Use stiff wire to clean the orifice (be careful not to chip it).
Reattach the bracket, pilot gas line, and thermocouple tube.
Turn on the gas and relight the pilot.
Cleaning the Burners
Clogged gas burners and ports heat inefficiently. Clean them at the start of the heating season.
To reach the ports, shut off the gas inlet valve and remove the bracket holding the pilot and thermocouple.
Remove any screws or nuts holding the burners and maneuver them out of the combustion chamber.
Scour the burners with a stiff wire brush.
Clean the burner ports with stiff wire that's slightly smaller than the diameter of the openings.
After cleaning, reassemble the burners in the combustion chamber, replacing any screws or nuts that secured the burners.
Mount the bracket holding the pilot and thermocouple.
Turn on the gas and relight the pilot.
Be sure to adjust the air-gas rate as explained below.
Adjusting the Burners
For maximum efficiency, burners fueled with natural gas should burn with a bright blue flame that has a soft blue green interior and no yellow tips. (Check with your gas company for the correct colors for other types of gas). To correct the air-natural gas ratio, you'll need to adjust the air shutters.
Turn up the thermostat so the burners light.
Loosen the lock screws.
Slowly open each shutter until the flames are bright blue.
Close the shutters gradually until yellow tips appear.
Slowly reopen the shutters until the yellow tips just disappear.
Tighten the screws.
Solving Pilot Problems
Pilots in gas burners may be electric or gas. For problems with electric pilots, call in a professional. Gas pilots can be relit and cleaned by the homeowner.
Lighting a Gas Pilot
Before you try to relight a pilot that has gone out, read the instructions usually printed on the front of the boiler or furnace. If there are none, have your utility company light it or follow these steps:
Use the manual control knob on the automatic gas valve to turn off the gas to the main burner and pilot.
Allow at least 5 minutes for accumulated gas to dissipate before proceeding.
Use extreme caution, and take more time if your fuel is bottled gas -- it doesn't dissipate readily.
When the gas has dissipated, set the thermostat well below room temperature.
Turn the manual control knob to PILOT and light the pilot, holding the knob there for a minute.
Release the knob and turn it to ON.
If the pilot doesn't stay on, call the gas company. (Remember to reset the thermostat when the pilot's relit).
Adjusting the Pilot Flame
The pilot flame should be blue and should cover the thermocouple. Before adjusting the flame, turn the thermostat down. Reset it when you're finished with the adjustment.
Cleaning The Pilot Orifice
If you have trouble lighting the pilot, the orifice may be plugged. To clean it:
Shut off the gas supply by turning the gas inlet valve handle so it's at a right angle to the pipe.
Disconnect the thermocouple tub and the pilot gas line from the automatic gas valve.
Remove the bracket holding the pilot and the thermocouple.
Use stiff wire to clean the orifice (be careful not to chip it).
Reattach the bracket, pilot gas line, and thermocouple tube.
Turn on the gas and relight the pilot.
Cleaning the Burners
Clogged gas burners and ports heat inefficiently. Clean them at the start of the heating season.
To reach the ports, shut off the gas inlet valve and remove the bracket holding the pilot and thermocouple.
Remove any screws or nuts holding the burners and maneuver them out of the combustion chamber.
Scour the burners with a stiff wire brush.
Clean the burner ports with stiff wire that's slightly smaller than the diameter of the openings.
After cleaning, reassemble the burners in the combustion chamber, replacing any screws or nuts that secured the burners.
Mount the bracket holding the pilot and thermocouple.
Turn on the gas and relight the pilot.
Be sure to adjust the air-gas rate as explained below.
Adjusting the Burners
For maximum efficiency, burners fueled with natural gas should burn with a bright blue flame that has a soft blue green interior and no yellow tips. (Check with your gas company for the correct colors for other types of gas). To correct the air-natural gas ratio, you'll need to adjust the air shutters.
Turn up the thermostat so the burners light.
Loosen the lock screws.
Slowly open each shutter until the flames are bright blue.
Close the shutters gradually until yellow tips appear.
Slowly reopen the shutters until the yellow tips just disappear.
Tighten the screws.
THE TOPICS OF MECHANICAL ENGINEERING
· The simple hierarchical list below tries to divide some of the fundamental topics found in engineering. It should be noted that this sort of division is somewhat subjective, although suitable for our purposes.
Engineering
Design
technology
systems
Analysis
solid mechanics
rigid solids
statics
equilibrium
trusses
method of joints
method of sections
frames
method of members
friction
dynamics
translation
rotation
collision
flexible solids
statics
hookes law
dynamics
collision
vibrations
fluids
compressible flow
incompressible flow
hydraulics
thermodynamics
Methods
metrology
laboratory techniques
manufacturing processes
Useful Information.
Useful Information.
Daily checks to be carried out.
Fuel
Cleanliness, quantity and a the state of the fuel filter.
Water
Quantity and condition of all the hoses, the radiator and the radiator cap .
Tyres
Including spare wheel, jack and repair outfit. Check the tyre pressures and also include the spare wheel. Look for thorns in the tyres in desert areas.
Oil
Quantity and colour. Also look for oil leaks around the engine.
Brakes
Check for operation, fluid level and fluid leaks, especially around the wheels.
Shock absorbers and suspension
Visually check the suspension and then bounce the corners of the vehicle to ascertain the condition of the shock absorbers. If the shock absorbers are faulty then the vehicle will carry on bouncing. Check the tightness of all wheel nuts.
Fan & alternator belts
Check for wear and slackness.
Cam belt (if fitted)
Check for wear and slackness.
Battery connections
Check the charge, water level and condition of the battery. Also check all of the supply leads from the battery.
Air filter
Check for both integrity and cleanliness (especially in dusty conditions).
Engine mounts
Check for wear especially in rough conditions. Rock the engine to ascertain how much wear there actually is in the engine mounts.
Grease points
A daily greasing is recommended if the vehicle has had to wade deep water.
Extras to carry and for the tool kit, in addition to the ones usually supplied :-
Water for both drinking and for the engine.
Spare fuel and funnel.
Extra lubricating oil.
First aid kit.
Radiator sealer (such as RAD WELD).
Puncture repair outfit with tyre levers.
An air pump for the inflation of the tyres.
Tyre pressure gauge.
Extra fan and alternator and cam belts.
Assortment of fuses and bulbs.
Insulation tape.
Hydraulic brake and clutch fluid.
12 volt voltage tester (light, buzzer or meter)
Spark plugs and rotor arm (for petrol engines)
Heavy-duty jumper leads.
Compression tester
A torch with spare batteries.
Most importantly. Do not forget, it is of little importance carrying such things as fan belts if you have not already checked that you have the required spanners with you. It is always a good policy to buy the highest quality tools available as there may be nobody around to borrow from in remote areas in the event of a breakage. Plus, a breaking tool can cause you injury
Daily checks to be carried out.
Fuel
Cleanliness, quantity and a the state of the fuel filter.
Water
Quantity and condition of all the hoses, the radiator and the radiator cap .
Tyres
Including spare wheel, jack and repair outfit. Check the tyre pressures and also include the spare wheel. Look for thorns in the tyres in desert areas.
Oil
Quantity and colour. Also look for oil leaks around the engine.
Brakes
Check for operation, fluid level and fluid leaks, especially around the wheels.
Shock absorbers and suspension
Visually check the suspension and then bounce the corners of the vehicle to ascertain the condition of the shock absorbers. If the shock absorbers are faulty then the vehicle will carry on bouncing. Check the tightness of all wheel nuts.
Fan & alternator belts
Check for wear and slackness.
Cam belt (if fitted)
Check for wear and slackness.
Battery connections
Check the charge, water level and condition of the battery. Also check all of the supply leads from the battery.
Air filter
Check for both integrity and cleanliness (especially in dusty conditions).
Engine mounts
Check for wear especially in rough conditions. Rock the engine to ascertain how much wear there actually is in the engine mounts.
Grease points
A daily greasing is recommended if the vehicle has had to wade deep water.
Extras to carry and for the tool kit, in addition to the ones usually supplied :-
Water for both drinking and for the engine.
Spare fuel and funnel.
Extra lubricating oil.
First aid kit.
Radiator sealer (such as RAD WELD).
Puncture repair outfit with tyre levers.
An air pump for the inflation of the tyres.
Tyre pressure gauge.
Extra fan and alternator and cam belts.
Assortment of fuses and bulbs.
Insulation tape.
Hydraulic brake and clutch fluid.
12 volt voltage tester (light, buzzer or meter)
Spark plugs and rotor arm (for petrol engines)
Heavy-duty jumper leads.
Compression tester
A torch with spare batteries.
Most importantly. Do not forget, it is of little importance carrying such things as fan belts if you have not already checked that you have the required spanners with you. It is always a good policy to buy the highest quality tools available as there may be nobody around to borrow from in remote areas in the event of a breakage. Plus, a breaking tool can cause you injury
Problem Solving.
Problem Solving.
Now that you are fully armed with some insights into the workings of both types of engines, I will now endeavour to explain some of the simple essentials used in fault finding.
The most important point to remember is that your fault-finding technique should be one of a "process of elimination". Start with the electrics, then move on to fuel and finally (once these have been eliminated) look for mechanical problems.
The following information will not be a substitute for a trained mechanic armed with many workshop manuals, but rather a conglomeration of tips and hints that will hopefully enable you to get out of trouble. It is, in my mind, advisable that everyone has some basic knowledge in the field as the knowledge and abilities of the local drivers cannot always be relied upon.
Now that you are fully armed with some insights into the workings of both types of engines, I will now endeavour to explain some of the simple essentials used in fault finding.
The most important point to remember is that your fault-finding technique should be one of a "process of elimination". Start with the electrics, then move on to fuel and finally (once these have been eliminated) look for mechanical problems.
The following information will not be a substitute for a trained mechanic armed with many workshop manuals, but rather a conglomeration of tips and hints that will hopefully enable you to get out of trouble. It is, in my mind, advisable that everyone has some basic knowledge in the field as the knowledge and abilities of the local drivers cannot always be relied upon.
Before attempting any diagnostics beware of the dangers.
Before attempting any diagnostics beware of the dangers.
Petrol is highly flammable so watch out for naked flames and sparks from the battery leads.
Battery acid contains sulphuric acid so be careful of spillage on clothes, skin or eyes. When charging a battery it gives off hydrogen gas so again watch out for sparks or naked flames.
The high tension leads in a petrol engine carry above 20,000 volts. This in itself is not harmful unless you have a heart condition, because there is very little current behind it, but you may injure yourself as you recoil from the shock.
Conversely, the battery can deliver a few hundred Amps of current (but low voltage. circa 12 volts). Here the danger is shorting out some of the wires in some way which could lead to a fire hazard.
Hydraulic brake fluid eats paint and corrodes rubber hoses etc.
Any moving parts must be treated with the utmost of respect so ensure all loose clothing is out of reach of these parts (i.e. A tie caught in the fan belt).
Badly fitting tools will slip under load and cause you to injure yourself.
Always prop up a vehicle raised by a jack, (just in case it fails or tilts), by using specially made tripods or wood supports. Back to the top
Trouble shooting Petrol Engines.
The engine will not turn over :-
If the engine does not turn over then the obvious place to start is the battery's state of charge and the condition of the terminals and leads emanating from it. Ensure that the terminal joints are clean and shiny. Both the copper (bright red metal) and the lead (soft grey metal) terminals can be cleaned with a penknife. Ensure all connections are tight. If this is all in order then turn on the headlights to check on the state of charge within the battery. If the battery and the fuses (Fuses melt in the event of an electrical overload and are found within the vehicles fuse box) for the ignition and starter solenoid are good then suspect the starter solenoid itself. (The starter solenoid is a component used to enable the small wire from the ignition switch to electrically close the contacts within the solenoid and thus allow it to pass the many hundreds of Amps that the starter motor requires to rotate the engine). To by-pass the starter solenoid connect one of your jump leads (from the tool kit) to the positive terminal of the battery and to the heavy cable on the starter itself (the one coming from the solenoid). Be very careful to avoid sparks and ensure the vehicle is out of gear. If all is good then suspect the starter motor brushes or windings.
The engine turn over slowly and the battery is good :-
Check for heat in the leads and terminals going to the starter. Heat means a resistance to the current and can be caused by frayed wires or corroded terminals. If the heat is generated within the starter motor (it will feel very hot to the touch) then suspect the windings.
The engine turns over but will not fire :-
First check to see if there is a spark at the sparking plugs. Connect a spare spark plug to one of the spark plug leads and then "ground" this plug to the engine block (by placing the threaded portion of the spark plug onto the engine block). If there is no spark then suspect the fuses that are in line with the wires to the coil and distributor. If there is voltage reaching here (you can find this with a voltmeter or the "light bulb tracer" found on page 15) then suspect the contact breakers within the distributor cap and ensure they have the right gap. (The contact breakers, within the distributor cap, regularly suffer from "pitting" of the contact surfaces and subsequent closure. This affects the ignition timing and can eventually lead to the engine not starting at all).
Some vehicles are fitted with electronic ignition which can be mostly discounted in the field as this system is far more reliable. Also inspect the cap inside and out for electrical "tracking". This will show up as crooked lines in the dirt of the cap. Any moisture will also lead the spark to follow the path of least resistance. Dry the components or expel the moisture using WD40 or another water repellent.
You can, in an emergency, by-pass the ignition switch by connecting a wire from the positive terminal of the battery directly to the high tension coil's "CB terminal". If the spark is visible on the spare plug it also could be that the plugs within the engine are fouled or have broken down. A weak plug will not spark under the load of compression as the voltage will find some other path to follow.
The engine has a good spark but will not fire :-
Suspect the fuel flow and quality of the fuel first. Check the tank, pipes from the tank, fuel filter and fuel pump. Lastly inspect the carburettor and air filter. With the air filter removed you will see fuel spray within the carburettor when the throttle is opened. Be careful here in case of a backfire and a flash back.
The engine turns over very quickly and smells of gasoline at the exhaust :-
In this case the engine is flooded with fuel. Remove the spark plugs and turn the engine over to expel the surplus fuel from within the cylinders. Then add a small amount of engine oil through the spark plug holes. This will boost the compression, which has been reduced by the petrol washing it away from the cylinder bores and piston rings.
All of the above are correct but the engine will still not fire :-
Check the ignition timing in case it has been altered and also the state of the toothed cam belt. If the toothed cam belt has too much free play it can slip a notch and thus displace the valve timing. Timing belts should always be replaced at the manufacturers specified intervals. More frequently if the vehicle is used in dusty or sandy conditions. Check that the compression is also within manufacturers limits by using a compression gauge in the place of a removed spark plug.
If a cylinder is not working :-
Pull off the spark plug leads in turn and listen to the engine tone.Be very careful as you could get a very high voltage shock. When a spark plug lead is removed from a bad cylinder the engine will not slow down and there will not be a change in the sound of the engine.
Once you have established which is the malfunctioning cylinder, increase the gap between the plug lead and the spark plug. You will here a clicking of the spark jumping the increased gap. This also boosts the spark voltage and can clean a fouled plug (fouled with carbon or oil) in some cases. If this fails then check the plug itself. Oily deposits on the plug indicates a failed plug or worn piston rings or worn valve guides. Black spark plugs are indicative of over fuelling "too rich a fuel / air mixture". White spark plug tips are indicative of over heating and too "weak" a fuel mixture. The correct colour is light brown to grey. It is worth mentioning here that the spark plugs must be of the specified type. All plugs are graduated in a heat range, also some plugs are or the "long reach" type whilst some are "short reach" and should never be mixed up.
If the engine is running unevenly and you have eliminated the spark :-
This could be the fuel flow through carburettor. One technique for clearing blocked carburettor jets is to rev. the engine up and close your hand over the carburettor briefly. This will draw an excess of fuel through the jets and often clear them. Be careful if you carry out this trick in case you get a flash back (flame back through the carburettor). If this does not clear the fault then a carburettor overhaul and clean is required.
Lack of compression :-
This is mainly due to a worn out or burnt valves (usually the exhaust). This is one of the reasons why it is of paramount importance to service the vehicle regularly and not forget to adjust the valve clearances at the same time. The other reason for lack of compression is that of worn piston rings or worn cylinder bores.
Inspection of the engine oil :-
If the engine oil is grey to white in colour then it has been contaminated with water (which has formed an emulsion with the oil). This is most probably due to a failure of the "cylinder head gasket" or the cylinder head itself being cracked. The "cylinder head gasket" is the seal between the engine block (main body of the engine) and the cylinder head (the smaller block on top of the main block that contains the spark plugs, valves etc.). The cylinder head gasket has to seal in the engine compression (and power stroke), plus seal in the cooling water and lubricating oil around the engine, so it is under a great strain and sometimes fails. Lesser amounts of water can build up in the oil due to repeated short distance running and the subsequent condensation. Water in the oil can also be ascertained by lighting the oil at the end of the dip-stick. If water is present then you will hear a crackling sound (e.g. bacon spitting in the pan).
Inspection of the exhaust :-
If the exhaust is black then this is a sign or over fuelling. If the exhaust is blue then it is a sign of lubrication oil being burnt with the fuel, (coming from worn piston rings, worn cylinder bores or worn valve guides). If the exhaust is very white and steamy then this is a sign of water passing through the engine (probably from the cylinder head gasket). If everything is in correct running order then the exhaust pipe metal itself will be white (for leaded fuel, this is the lead) or brown (for unleaded fuel).
Petrol is highly flammable so watch out for naked flames and sparks from the battery leads.
Battery acid contains sulphuric acid so be careful of spillage on clothes, skin or eyes. When charging a battery it gives off hydrogen gas so again watch out for sparks or naked flames.
The high tension leads in a petrol engine carry above 20,000 volts. This in itself is not harmful unless you have a heart condition, because there is very little current behind it, but you may injure yourself as you recoil from the shock.
Conversely, the battery can deliver a few hundred Amps of current (but low voltage. circa 12 volts). Here the danger is shorting out some of the wires in some way which could lead to a fire hazard.
Hydraulic brake fluid eats paint and corrodes rubber hoses etc.
Any moving parts must be treated with the utmost of respect so ensure all loose clothing is out of reach of these parts (i.e. A tie caught in the fan belt).
Badly fitting tools will slip under load and cause you to injure yourself.
Always prop up a vehicle raised by a jack, (just in case it fails or tilts), by using specially made tripods or wood supports. Back to the top
Trouble shooting Petrol Engines.
The engine will not turn over :-
If the engine does not turn over then the obvious place to start is the battery's state of charge and the condition of the terminals and leads emanating from it. Ensure that the terminal joints are clean and shiny. Both the copper (bright red metal) and the lead (soft grey metal) terminals can be cleaned with a penknife. Ensure all connections are tight. If this is all in order then turn on the headlights to check on the state of charge within the battery. If the battery and the fuses (Fuses melt in the event of an electrical overload and are found within the vehicles fuse box) for the ignition and starter solenoid are good then suspect the starter solenoid itself. (The starter solenoid is a component used to enable the small wire from the ignition switch to electrically close the contacts within the solenoid and thus allow it to pass the many hundreds of Amps that the starter motor requires to rotate the engine). To by-pass the starter solenoid connect one of your jump leads (from the tool kit) to the positive terminal of the battery and to the heavy cable on the starter itself (the one coming from the solenoid). Be very careful to avoid sparks and ensure the vehicle is out of gear. If all is good then suspect the starter motor brushes or windings.
The engine turn over slowly and the battery is good :-
Check for heat in the leads and terminals going to the starter. Heat means a resistance to the current and can be caused by frayed wires or corroded terminals. If the heat is generated within the starter motor (it will feel very hot to the touch) then suspect the windings.
The engine turns over but will not fire :-
First check to see if there is a spark at the sparking plugs. Connect a spare spark plug to one of the spark plug leads and then "ground" this plug to the engine block (by placing the threaded portion of the spark plug onto the engine block). If there is no spark then suspect the fuses that are in line with the wires to the coil and distributor. If there is voltage reaching here (you can find this with a voltmeter or the "light bulb tracer" found on page 15) then suspect the contact breakers within the distributor cap and ensure they have the right gap. (The contact breakers, within the distributor cap, regularly suffer from "pitting" of the contact surfaces and subsequent closure. This affects the ignition timing and can eventually lead to the engine not starting at all).
Some vehicles are fitted with electronic ignition which can be mostly discounted in the field as this system is far more reliable. Also inspect the cap inside and out for electrical "tracking". This will show up as crooked lines in the dirt of the cap. Any moisture will also lead the spark to follow the path of least resistance. Dry the components or expel the moisture using WD40 or another water repellent.
You can, in an emergency, by-pass the ignition switch by connecting a wire from the positive terminal of the battery directly to the high tension coil's "CB terminal". If the spark is visible on the spare plug it also could be that the plugs within the engine are fouled or have broken down. A weak plug will not spark under the load of compression as the voltage will find some other path to follow.
The engine has a good spark but will not fire :-
Suspect the fuel flow and quality of the fuel first. Check the tank, pipes from the tank, fuel filter and fuel pump. Lastly inspect the carburettor and air filter. With the air filter removed you will see fuel spray within the carburettor when the throttle is opened. Be careful here in case of a backfire and a flash back.
The engine turns over very quickly and smells of gasoline at the exhaust :-
In this case the engine is flooded with fuel. Remove the spark plugs and turn the engine over to expel the surplus fuel from within the cylinders. Then add a small amount of engine oil through the spark plug holes. This will boost the compression, which has been reduced by the petrol washing it away from the cylinder bores and piston rings.
All of the above are correct but the engine will still not fire :-
Check the ignition timing in case it has been altered and also the state of the toothed cam belt. If the toothed cam belt has too much free play it can slip a notch and thus displace the valve timing. Timing belts should always be replaced at the manufacturers specified intervals. More frequently if the vehicle is used in dusty or sandy conditions. Check that the compression is also within manufacturers limits by using a compression gauge in the place of a removed spark plug.
If a cylinder is not working :-
Pull off the spark plug leads in turn and listen to the engine tone.Be very careful as you could get a very high voltage shock. When a spark plug lead is removed from a bad cylinder the engine will not slow down and there will not be a change in the sound of the engine.
Once you have established which is the malfunctioning cylinder, increase the gap between the plug lead and the spark plug. You will here a clicking of the spark jumping the increased gap. This also boosts the spark voltage and can clean a fouled plug (fouled with carbon or oil) in some cases. If this fails then check the plug itself. Oily deposits on the plug indicates a failed plug or worn piston rings or worn valve guides. Black spark plugs are indicative of over fuelling "too rich a fuel / air mixture". White spark plug tips are indicative of over heating and too "weak" a fuel mixture. The correct colour is light brown to grey. It is worth mentioning here that the spark plugs must be of the specified type. All plugs are graduated in a heat range, also some plugs are or the "long reach" type whilst some are "short reach" and should never be mixed up.
If the engine is running unevenly and you have eliminated the spark :-
This could be the fuel flow through carburettor. One technique for clearing blocked carburettor jets is to rev. the engine up and close your hand over the carburettor briefly. This will draw an excess of fuel through the jets and often clear them. Be careful if you carry out this trick in case you get a flash back (flame back through the carburettor). If this does not clear the fault then a carburettor overhaul and clean is required.
Lack of compression :-
This is mainly due to a worn out or burnt valves (usually the exhaust). This is one of the reasons why it is of paramount importance to service the vehicle regularly and not forget to adjust the valve clearances at the same time. The other reason for lack of compression is that of worn piston rings or worn cylinder bores.
Inspection of the engine oil :-
If the engine oil is grey to white in colour then it has been contaminated with water (which has formed an emulsion with the oil). This is most probably due to a failure of the "cylinder head gasket" or the cylinder head itself being cracked. The "cylinder head gasket" is the seal between the engine block (main body of the engine) and the cylinder head (the smaller block on top of the main block that contains the spark plugs, valves etc.). The cylinder head gasket has to seal in the engine compression (and power stroke), plus seal in the cooling water and lubricating oil around the engine, so it is under a great strain and sometimes fails. Lesser amounts of water can build up in the oil due to repeated short distance running and the subsequent condensation. Water in the oil can also be ascertained by lighting the oil at the end of the dip-stick. If water is present then you will hear a crackling sound (e.g. bacon spitting in the pan).
Inspection of the exhaust :-
If the exhaust is black then this is a sign or over fuelling. If the exhaust is blue then it is a sign of lubrication oil being burnt with the fuel, (coming from worn piston rings, worn cylinder bores or worn valve guides). If the exhaust is very white and steamy then this is a sign of water passing through the engine (probably from the cylinder head gasket). If everything is in correct running order then the exhaust pipe metal itself will be white (for leaded fuel, this is the lead) or brown (for unleaded fuel).
DIESEL ENGINES
Diesel Engines
Diesel (also know as Gasoleo by the Spanish and Mazout by the French) has an oily texture and a pungent smell. Diesel does not evaporate very quickly and is more difficult to ignite when compared to gasoline. It is also incredibly difficult to remove from clothing so be careful when filling vehicles or bleeding fuel lines.
The main differences from the gasoline engine are :-
The spark plug replaced by an injector nozzle. Which is used for delivering a fine mist of diesel into the cylinder.
Because of the use of an injector, there is no need for a carburettor to supply the fuel in the right form.
Because the fuel self ignites due to the heat caused by the higher compression there is no need foranair THE INDUCTION STROKE (first cycle)
y of the spark generating and distributing components used in the gasoline engine.
THE In this cycle the crankshaft rotates thus drawing the piston down the cylinder bore. This action draws pure air alone into the cylinder via the opened inlet valve. The exhaust valve is closed at this time.
THE COMPRESSION STROKE (second cycle)
Both the exhaust valve and inlet valve are now closed.
The crankshaft continues to rotate and this action forces the piston back up the cylinder bore. As a result of both valves being closed the pure air has nowhere to go, so compression of the air now takes place.
The ratio of compression is typically in the range of between (16 to 1) to (22 to 1) depending on the engines designed performance. This is much higher than that found in the gasoline engine and as a result the air temperature rises to well above 500 degrees Centigrade.This has now completed one revolution of the crankshaft.
THE POWER STROKE (third cycle)
Both the exhaust valve and the inlet valve remain closed.
The fuel is now sprayed into the heated air just before the piston reaches the top of its stroke and as a result it ignites and burns with the oxygen in the air.
This results in a rapid burning (expansion) of the gasses which forces the piston back down the cylinder bore, and in the process turns the crankshaft.
This is Power.....
THE EXHAUST STROKE (forth cycle)
The inlet valve remains closed but the exhaust valve is now opened.
The crankshaft continues to turn, forcing the piston back up the cylinder bore.
Because the exhaust valve is now open the movement of the piston forces the burnt gasses out of the cylinder, through the silencer and out into the atmosphere.
This has now completed the second revolution of the crankshaft. The whole process is now ready to begin again at the induction stroke.
Re-Cap
The petrol "spark ignition" fuel engine, is more wasteful of fuel than the diesel engine. Fuel has a certain heat value, and heat is work. The petrol engine delivers only 22 -- 25 % of the theoretical work value of its fuel, while the diesel engine delivers 30 -- 36 %. (First advantage). Thus the diesel engine is said to have the higher thermal efficiency, which in terms of ordinary usage means that there will be a more economical consumption figure for a given load. The lower temperature, at which petrol ignites compared to diesel, limits the compression ratio within the petrol engine to a lower figure. It is known that the higher the compression the more efficient an engine becomes, so this gives the diesel engine its second advantage, because only pure air is compressed so that there is nothing to "pre-ignite". (You can hear pre-ignition in a petrol engine that has too far advanced timing of the spark. This manifests itself as a "rattle" when you are driving with wide throttle openings and occurs particularly at lower revs. This can also lead to the engine carrying on firing, and running, when the ignition key is turned off)
Just before the piston reaches the end of the compression stroke the diesel is injected into the combustion chamber through an injector nozzle mounted in the cylinder head (in much the same position as the spark plug in a petrol engine). During injection the fuel is split up into finely divided particles, and the mixture of these with the air forms an explosive charge that is ignited by the heat of the compression. Injection, of the fuel, is continued for a short period, during which the piston passes its highest position and begins to descend on the power stroke. The expansion of combustion only begins to have effect when the piston has passed the top of its stroke. When the fuel is cut off expansion of the gases still continues. The overall effect on the piston is a more sustained pressure than that associated with the petrol engine. (In other words the burning and expansion lasts much longer than in a gasoline engine).
To inject the fuel a special type of pump driven by the engine is employed and this is the distinguishing feature of the diesel engine. This pump also has to supply the fuel at just the right instant "injection timing" for the engine to work efficiently. A very important detail is that injection must cease cleanly and abruptly at the end of the delivery period without any trace of "after-dribble" of the fuel from the injector otherwise carbon deposits quickly form on the nozzle tip and excessive smoke will appear in the exhaust.
So, already you should see that the diesel engine has no high voltage electrics to go wrong and be affected by moisture as in the petrol engine (wet high voltage leads in the petrol engine will stop it from running as the high voltage will find an easier path to follow along the wet leads). Also, the diesel's higher thermal efficiency means lower running temperatures so there are less overheating problems in arduous conditions. And because of the higher compression ratios encountered, diesel engines are built far more strongly than the petrol engine thus helping its durability and reliability in the field.
The maximum speed of the diesel engine is also kept to lower revolutions per minute (RPM) than that found in the petrol engine. This is accomplished by the use of a governor. This means that speed regulation (as in power generators) is reliably controlled so that when there is no load on the engine the fuel supply is cut back. But once load is applied then the fuel supply is increased to maintain the set RPM.
Diesel (also know as Gasoleo by the Spanish and Mazout by the French) has an oily texture and a pungent smell. Diesel does not evaporate very quickly and is more difficult to ignite when compared to gasoline. It is also incredibly difficult to remove from clothing so be careful when filling vehicles or bleeding fuel lines.
The main differences from the gasoline engine are :-
The spark plug replaced by an injector nozzle. Which is used for delivering a fine mist of diesel into the cylinder.
Because of the use of an injector, there is no need for a carburettor to supply the fuel in the right form.
Because the fuel self ignites due to the heat caused by the higher compression there is no need foranair THE INDUCTION STROKE (first cycle)
y of the spark generating and distributing components used in the gasoline engine.
THE In this cycle the crankshaft rotates thus drawing the piston down the cylinder bore. This action draws pure air alone into the cylinder via the opened inlet valve. The exhaust valve is closed at this time.
THE COMPRESSION STROKE (second cycle)
Both the exhaust valve and inlet valve are now closed.
The crankshaft continues to rotate and this action forces the piston back up the cylinder bore. As a result of both valves being closed the pure air has nowhere to go, so compression of the air now takes place.
The ratio of compression is typically in the range of between (16 to 1) to (22 to 1) depending on the engines designed performance. This is much higher than that found in the gasoline engine and as a result the air temperature rises to well above 500 degrees Centigrade.This has now completed one revolution of the crankshaft.
THE POWER STROKE (third cycle)
Both the exhaust valve and the inlet valve remain closed.
The fuel is now sprayed into the heated air just before the piston reaches the top of its stroke and as a result it ignites and burns with the oxygen in the air.
This results in a rapid burning (expansion) of the gasses which forces the piston back down the cylinder bore, and in the process turns the crankshaft.
This is Power.....
THE EXHAUST STROKE (forth cycle)
The inlet valve remains closed but the exhaust valve is now opened.
The crankshaft continues to turn, forcing the piston back up the cylinder bore.
Because the exhaust valve is now open the movement of the piston forces the burnt gasses out of the cylinder, through the silencer and out into the atmosphere.
This has now completed the second revolution of the crankshaft. The whole process is now ready to begin again at the induction stroke.
Re-Cap
The petrol "spark ignition" fuel engine, is more wasteful of fuel than the diesel engine. Fuel has a certain heat value, and heat is work. The petrol engine delivers only 22 -- 25 % of the theoretical work value of its fuel, while the diesel engine delivers 30 -- 36 %. (First advantage). Thus the diesel engine is said to have the higher thermal efficiency, which in terms of ordinary usage means that there will be a more economical consumption figure for a given load. The lower temperature, at which petrol ignites compared to diesel, limits the compression ratio within the petrol engine to a lower figure. It is known that the higher the compression the more efficient an engine becomes, so this gives the diesel engine its second advantage, because only pure air is compressed so that there is nothing to "pre-ignite". (You can hear pre-ignition in a petrol engine that has too far advanced timing of the spark. This manifests itself as a "rattle" when you are driving with wide throttle openings and occurs particularly at lower revs. This can also lead to the engine carrying on firing, and running, when the ignition key is turned off)
Just before the piston reaches the end of the compression stroke the diesel is injected into the combustion chamber through an injector nozzle mounted in the cylinder head (in much the same position as the spark plug in a petrol engine). During injection the fuel is split up into finely divided particles, and the mixture of these with the air forms an explosive charge that is ignited by the heat of the compression. Injection, of the fuel, is continued for a short period, during which the piston passes its highest position and begins to descend on the power stroke. The expansion of combustion only begins to have effect when the piston has passed the top of its stroke. When the fuel is cut off expansion of the gases still continues. The overall effect on the piston is a more sustained pressure than that associated with the petrol engine. (In other words the burning and expansion lasts much longer than in a gasoline engine).
To inject the fuel a special type of pump driven by the engine is employed and this is the distinguishing feature of the diesel engine. This pump also has to supply the fuel at just the right instant "injection timing" for the engine to work efficiently. A very important detail is that injection must cease cleanly and abruptly at the end of the delivery period without any trace of "after-dribble" of the fuel from the injector otherwise carbon deposits quickly form on the nozzle tip and excessive smoke will appear in the exhaust.
So, already you should see that the diesel engine has no high voltage electrics to go wrong and be affected by moisture as in the petrol engine (wet high voltage leads in the petrol engine will stop it from running as the high voltage will find an easier path to follow along the wet leads). Also, the diesel's higher thermal efficiency means lower running temperatures so there are less overheating problems in arduous conditions. And because of the higher compression ratios encountered, diesel engines are built far more strongly than the petrol engine thus helping its durability and reliability in the field.
The maximum speed of the diesel engine is also kept to lower revolutions per minute (RPM) than that found in the petrol engine. This is accomplished by the use of a governor. This means that speed regulation (as in power generators) is reliably controlled so that when there is no load on the engine the fuel supply is cut back. But once load is applied then the fuel supply is increased to maintain the set RPM.
FUNCTIONING OF ENGINE
VALVE TIMING
The valves are opened by the CAMSHAFT. The camshaft is in essence just a bar of metal with projections (CAMS) sticking out along its length. As the camshaft rotates these projections move the valves to an open position.
Valve closure is accomplished by the use of springs. The position of the projections on the Camshaft is set by the manufacturer but the controlling of the rotation is governed by its assembly into the engine. The camshaft rotates at half of the speed of the crankshaft and is driven from the crankshaft via gears, chains or a toothed rubber belt.
On all engines you will find "timing" marks to help you re-align the camshaft on re-assembly (i.e. The installation of a new toothed belt).
If there are no timing marks to be found, then, an approximate timing can be afforded be positioning the first piston at the top (TDC Top Dead Centre) and setting both valves to overlap (exhaust nearly closed and the intake nearly open).
IGNITION TIMING
The spark itself is produced in a transformer coil (high-tension coil). This coil converts the 12 volts from the battery into many thousands of volts and is created at just the right moment by the opening of a "contact breaker" or electronically by the use of magnets and "Hall effect transistors" (electronic ignition).
As you can imagine the spark generation also has to be at the right time. Too late and the ignition is "retarded" causing overheating due to the very small power output. Too early and the engine will probably backfire, (through the carburettor), run very roughly and sound terrible.
This is all controlled by the positioning of the "Distributor". The drive to most contact breaker shafts is also at half of the crankshaft speed. The distributor is employed for "distributing" the high voltage to the correct cylinder's spark plug. You will see a plastic cap with many leads ensuing. One lead you can trace back to the high-tension coil. The total number of the other leads matches that of the number of cylinders in the engine. The high voltage enters the centre of the distributor cap and is fed via the "rotor arm" to one of the other leads that go to the spark plugs in the "cylinder head". These are set to the "Firing Order" of the engine, which is usually embossed somewhere on the intake manifold. The firing order on a four-cylinder engine might be for example --1, 3, 4, 2 --.
So with this information you can replace these leads if they have become inadvertently mixed up. All you need to ascertain is the direction of rotation of the "Rotor Arm" within the distributor by turning the engine over (with the use of the ignition key or by selecting a low gear and pushing the vehicle forward). Then you replace the leads in the order given (i.e. 1, 3, 4, 2) following the direction of rotation you ascertained from above. The number 1 cylinder is usually nearest to the radiator (front of the car).
The first lead you connect is the most critical for getting the whole sequence in the correct order. The rotor arm will be pointing at one of the leads and this lead must go to the cylinder that is under compression at that time. (This is ascertained by observing which cylinder has not got a valve open at that time).
THE CARBURETTOR
The carburettor controls the amount of fuel in relation to the amount of air that enters the engine. This is carried out by the deployment of a butterfly valve, which is linked in turn to the throttle pedal in the vehicle.
The ratio of Fuel to Air is determined by the size of the holes in the "JETS" within the carburettor and is set by the engine designers. But other factors do come into play. The "choke" for example restricts the airflow in the carburettor and thus more fuel, in turn, is administered to the engine (necessary to compensate for the condensation of fuel inside a cold engine). Also a blocked air filter will have the same effect of restricting the air and forcing more fuel into the engine causing fuel wastage through inefficiency and poor running of the engine. Blocked "Jets" on the other hand allow less fuel to enter the engine and weaken the mixture giving rise to overheating and also poor running.
The valves are opened by the CAMSHAFT. The camshaft is in essence just a bar of metal with projections (CAMS) sticking out along its length. As the camshaft rotates these projections move the valves to an open position.
Valve closure is accomplished by the use of springs. The position of the projections on the Camshaft is set by the manufacturer but the controlling of the rotation is governed by its assembly into the engine. The camshaft rotates at half of the speed of the crankshaft and is driven from the crankshaft via gears, chains or a toothed rubber belt.
On all engines you will find "timing" marks to help you re-align the camshaft on re-assembly (i.e. The installation of a new toothed belt).
If there are no timing marks to be found, then, an approximate timing can be afforded be positioning the first piston at the top (TDC Top Dead Centre) and setting both valves to overlap (exhaust nearly closed and the intake nearly open).
IGNITION TIMING
The spark itself is produced in a transformer coil (high-tension coil). This coil converts the 12 volts from the battery into many thousands of volts and is created at just the right moment by the opening of a "contact breaker" or electronically by the use of magnets and "Hall effect transistors" (electronic ignition).
As you can imagine the spark generation also has to be at the right time. Too late and the ignition is "retarded" causing overheating due to the very small power output. Too early and the engine will probably backfire, (through the carburettor), run very roughly and sound terrible.
This is all controlled by the positioning of the "Distributor". The drive to most contact breaker shafts is also at half of the crankshaft speed. The distributor is employed for "distributing" the high voltage to the correct cylinder's spark plug. You will see a plastic cap with many leads ensuing. One lead you can trace back to the high-tension coil. The total number of the other leads matches that of the number of cylinders in the engine. The high voltage enters the centre of the distributor cap and is fed via the "rotor arm" to one of the other leads that go to the spark plugs in the "cylinder head". These are set to the "Firing Order" of the engine, which is usually embossed somewhere on the intake manifold. The firing order on a four-cylinder engine might be for example --1, 3, 4, 2 --.
So with this information you can replace these leads if they have become inadvertently mixed up. All you need to ascertain is the direction of rotation of the "Rotor Arm" within the distributor by turning the engine over (with the use of the ignition key or by selecting a low gear and pushing the vehicle forward). Then you replace the leads in the order given (i.e. 1, 3, 4, 2) following the direction of rotation you ascertained from above. The number 1 cylinder is usually nearest to the radiator (front of the car).
The first lead you connect is the most critical for getting the whole sequence in the correct order. The rotor arm will be pointing at one of the leads and this lead must go to the cylinder that is under compression at that time. (This is ascertained by observing which cylinder has not got a valve open at that time).
THE CARBURETTOR
The carburettor controls the amount of fuel in relation to the amount of air that enters the engine. This is carried out by the deployment of a butterfly valve, which is linked in turn to the throttle pedal in the vehicle.
The ratio of Fuel to Air is determined by the size of the holes in the "JETS" within the carburettor and is set by the engine designers. But other factors do come into play. The "choke" for example restricts the airflow in the carburettor and thus more fuel, in turn, is administered to the engine (necessary to compensate for the condensation of fuel inside a cold engine). Also a blocked air filter will have the same effect of restricting the air and forcing more fuel into the engine causing fuel wastage through inefficiency and poor running of the engine. Blocked "Jets" on the other hand allow less fuel to enter the engine and weaken the mixture giving rise to overheating and also poor running.
THE POWER STROKE (third cycle)
Both the exhaust valve and the inlet valve remain closed.
Just before the piston reaches the top of its stroke a high voltage is created within the "High Tension Coil" and is fed (via the distributor) to the spark plug. This high voltage jumps the gap between the spark plug contacts and ignites the compressed gasoline / air mixture.
This results in a rapid burning (expansion) of the gasses which forces the piston back down the cylinder bore, and in the process turns the crankshaft. This is Power.....
THE EXHAUST STROKE (forth cycle)
The inlet valve remains closed but the exhaust valve is now opened.
The crankshaft continues to turn, forcing the piston back up the cylinder bore.
Because the exhaust valve is now open the movement of the piston forces the burnt gasses out of the cylinder, through the silencer and out into the atmosphere.
This has now completed the second revolution of the crankshaft. The whole process is now ready to begin again at the induction stroke.
With this short explanation and the aid of these simple sketches I hope you can now grasp some of the important issues taking place here. The sequence (TIMING) of movement of the components is of prime importance. The valves must open and close in the correct order and the spark must arrive at just the right time to ignite the fuel / air mixture. Also the fuel / air mixture from the carburettor must not be too rich (too much fuel) or too weak (too little fuel known as lean).
Both the exhaust valve and the inlet valve remain closed.
Just before the piston reaches the top of its stroke a high voltage is created within the "High Tension Coil" and is fed (via the distributor) to the spark plug. This high voltage jumps the gap between the spark plug contacts and ignites the compressed gasoline / air mixture.
This results in a rapid burning (expansion) of the gasses which forces the piston back down the cylinder bore, and in the process turns the crankshaft. This is Power.....
THE EXHAUST STROKE (forth cycle)
The inlet valve remains closed but the exhaust valve is now opened.
The crankshaft continues to turn, forcing the piston back up the cylinder bore.
Because the exhaust valve is now open the movement of the piston forces the burnt gasses out of the cylinder, through the silencer and out into the atmosphere.
This has now completed the second revolution of the crankshaft. The whole process is now ready to begin again at the induction stroke.
With this short explanation and the aid of these simple sketches I hope you can now grasp some of the important issues taking place here. The sequence (TIMING) of movement of the components is of prime importance. The valves must open and close in the correct order and the spark must arrive at just the right time to ignite the fuel / air mixture. Also the fuel / air mixture from the carburettor must not be too rich (too much fuel) or too weak (too little fuel known as lean).
GASOLINE Engines
GASOLINE (also know as petrol, Benzene and Gasolina) evaporates very quickly giving off highly inflammable vapours. With any gasoline spillage be extremely careful of any naked flames or sparks (i.e. from the vehicles electrical system, welding equipment, cigarettes etc).
THE INDUCTION STROKE (first cycle)
The figure to the left is a simplified cut-away drawing of the internals of a single cylinder engine.
The drawing represents the Piston moving down the cylinder.
The piston is attached to the Crankshaft by means of a connecting rod. As the crankshaft rotates the connecting rod draws the piston downwards.
(The crankshaft rotates clockwise in these diagrams)
Gasoline is converted into a fine mist with the outside air inside a carburettor or an injection system (Both types are not shown in the drawing).
The inlet valve is opened and thus allows the entering of the gasoline and air mixture, into the cylinder, in readiness for the next cycle. During this cycle the exhaust valve remains closed.
THE COMPRESSION STROKE (second cycle)
Both the exhaust valve and the inlet valve are now closed.
The crankshaft continues to rotate, with the aid of a flywheel, and this action forces the piston back up the cylinder bore. As a result of both valves being closed the gasoline / air mixture has nowhere to go, so compression now takes place. The ratio of compression is typically in the range of between (7 to 1) to (11 to 1) depending on the engines designed performance.
The "compression ratio" is that of the ratio of the total volume of the cylinder above the piston when it is in it's lowest position to that of the "combustion" or clearance space when it is at its highest position. (In other words, if 10 cm of air in a bicycle pump were compressed into 1 cm then you would have a "compression ratio" of "10 to 1").
This has now completed one revolution of the crankshaft.
GASOLINE (also know as petrol, Benzene and Gasolina) evaporates very quickly giving off highly inflammable vapours. With any gasoline spillage be extremely careful of any naked flames or sparks (i.e. from the vehicles electrical system, welding equipment, cigarettes etc).
THE INDUCTION STROKE (first cycle)
The figure to the left is a simplified cut-away drawing of the internals of a single cylinder engine.
The drawing represents the Piston moving down the cylinder.
The piston is attached to the Crankshaft by means of a connecting rod. As the crankshaft rotates the connecting rod draws the piston downwards.
(The crankshaft rotates clockwise in these diagrams)
Gasoline is converted into a fine mist with the outside air inside a carburettor or an injection system (Both types are not shown in the drawing).
The inlet valve is opened and thus allows the entering of the gasoline and air mixture, into the cylinder, in readiness for the next cycle. During this cycle the exhaust valve remains closed.
THE COMPRESSION STROKE (second cycle)
Both the exhaust valve and the inlet valve are now closed.
The crankshaft continues to rotate, with the aid of a flywheel, and this action forces the piston back up the cylinder bore. As a result of both valves being closed the gasoline / air mixture has nowhere to go, so compression now takes place. The ratio of compression is typically in the range of between (7 to 1) to (11 to 1) depending on the engines designed performance.
The "compression ratio" is that of the ratio of the total volume of the cylinder above the piston when it is in it's lowest position to that of the "combustion" or clearance space when it is at its highest position. (In other words, if 10 cm of air in a bicycle pump were compressed into 1 cm then you would have a "compression ratio" of "10 to 1").
This has now completed one revolution of the crankshaft.
Overview of the internal combustion engine
Problem solving for diesel engines.
Useful information.
Overview of the internal combustion engine.
To be able to carry out any form of fault diagnosis, and maybe even an emergency repair, it is of great advantage if you are first acquainted with the general principals of the internal combustion engine. You do not, on the other hand, need to know all of the technical details just to have an overview of the workings in your minds eye.
A few basic principals of the workings of a diesel engine, for example, apply to diesel cars, trucks, generators and large marine engines. Yes they are all the same but they have different components of different sizes and usually placed in slightly different positions. The working principal, though, still remains the same.
To simplify matters we are going to deal with what takes place in just one cylinder of a gasoline engine and one cylinder of diesel engines through their full running cycle. The same principals will apply regardless of how many cylinders are actually used in a particular engine.
Also we are only going to discuss the four-stroke cycle (fully explained in the later text) for diesels and gasoline engines. There is also the two stroke cycle in use, but it is only generally found in use in smaller capacity engines (such as some small generators, chain saws, outboard motors and some small motor cycles).
First of all, and probably most important, what exactly is meant by the term Internal Combustion Engine?
Simply put it means the burning of a flammable substance (fuel) inside the engine, the substance in this case being either Diesel Oil or Gasoline (petrol). This burning of the fuel is where these engines derive their power from and just how it transpires is dealt with in the following sections under the headings Gasoline Engines and Diesel Engines.
Secondly, what exactly is meant by the term FOUR-STROKE cycle ?
To derive it's power from the heat of the burning fuel the four stroke engine (whether diesel or gasoline) has to complete four separate cycles. The completion of four piston cycles takes 2 complete crankshaft revolutions. These cycles are explained in greater detail, (together with the aid of sketches), in the next two sections of this work, but briefly, look below for a brief overview.
Induction
Intake (suction) of air alone (in a diesel engine), or, air and gasoline vapour in a gasoline engine.
Compression
Compressing of the above gases.
This completes the first revolution of the crankshaft.
POWER
Igniting of the compressed gasoline vapour by a spark within a gasoline engine, or, the injection of a diesel mist through an injector, which then self ignites due to the heat, generated by compressing the air. This produces a rapid expansion and therefore power.
EXHAUST
The blowing out of the spent gases. And then the process starts all over. This completes the second revolution of the crankshaft.
TIPS BY RAMESHKUMAR
Useful information.
Overview of the internal combustion engine.
To be able to carry out any form of fault diagnosis, and maybe even an emergency repair, it is of great advantage if you are first acquainted with the general principals of the internal combustion engine. You do not, on the other hand, need to know all of the technical details just to have an overview of the workings in your minds eye.
A few basic principals of the workings of a diesel engine, for example, apply to diesel cars, trucks, generators and large marine engines. Yes they are all the same but they have different components of different sizes and usually placed in slightly different positions. The working principal, though, still remains the same.
To simplify matters we are going to deal with what takes place in just one cylinder of a gasoline engine and one cylinder of diesel engines through their full running cycle. The same principals will apply regardless of how many cylinders are actually used in a particular engine.
Also we are only going to discuss the four-stroke cycle (fully explained in the later text) for diesels and gasoline engines. There is also the two stroke cycle in use, but it is only generally found in use in smaller capacity engines (such as some small generators, chain saws, outboard motors and some small motor cycles).
First of all, and probably most important, what exactly is meant by the term Internal Combustion Engine?
Simply put it means the burning of a flammable substance (fuel) inside the engine, the substance in this case being either Diesel Oil or Gasoline (petrol). This burning of the fuel is where these engines derive their power from and just how it transpires is dealt with in the following sections under the headings Gasoline Engines and Diesel Engines.
Secondly, what exactly is meant by the term FOUR-STROKE cycle ?
To derive it's power from the heat of the burning fuel the four stroke engine (whether diesel or gasoline) has to complete four separate cycles. The completion of four piston cycles takes 2 complete crankshaft revolutions. These cycles are explained in greater detail, (together with the aid of sketches), in the next two sections of this work, but briefly, look below for a brief overview.
Induction
Intake (suction) of air alone (in a diesel engine), or, air and gasoline vapour in a gasoline engine.
Compression
Compressing of the above gases.
This completes the first revolution of the crankshaft.
POWER
Igniting of the compressed gasoline vapour by a spark within a gasoline engine, or, the injection of a diesel mist through an injector, which then self ignites due to the heat, generated by compressing the air. This produces a rapid expansion and therefore power.
EXHAUST
The blowing out of the spent gases. And then the process starts all over. This completes the second revolution of the crankshaft.
TIPS BY RAMESHKUMAR
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RAMESH KUMAR
AIRCRAFT TECHNICIAN
manikanta
mechanical works