Car mechanics: Engine Workings

An engine is an awesome piece of engineering technology that uses many parts to function. All of these parts has a very important function. However, there are literally hundreds of parts within an engine so I am only going to show you the most important/main parts and their functions.

An internal combustion engine uses thousands of tiny, controlled explosions to create power and torque (that's why its called a combustion engine because it uses fuel combustion to function). Car engines are Four Stroke and that is what I am going to focus on. These four strokes detail the sequence of engine function and they are: Induction, Compression, Power (combustion), and Exhaust. Specific groups and systems of parts are responsible for these strokes.

First of the systems/parts is the Induction system. This consists of the filter, the mass flow sensor, throttle body, and the intake manifold. The induction system is responsible for sucking air into the engine that mixes with the fuel and is compressed to provide power during the combustion stroke. The filter ensures that dirt and debris from the air does not get into the engine and possible contaminate the engine oil and cause excessive wear by catching it within the material of the filter. Over time these filters get clogged up and dirty which allows dirt into the engine and restricts air flow which is why they must eventually be cleaned or replaced. These filters are made using a variety of different materials including pleated paper, polyurethane foam and also cotton which are all lightly oiled. The mass flow sensor controls airflow into the engine based on fuel injection and regulates accordingly to make the engine run smoother. These sometimes need to be cleaned with a special cleaning solution sold by auto part stores and in some occasions they need to be replaced. The throttle body serves as a sort of conduit between the filter/sensor and into the engine itself. It has a flap that allows more or less air into the engine based on the throttle input (pressing harder on the gas pedal pulls on the throttle cable which opens up the throttle flap, moving it which allows air volume to increase and increasing power). And finally the intake manifold is the pathway through which air travels through the other induction parts and into the engine intake valve itself where it mixes with the fuel spray from the fuel injector and is compressed by the piston and finally ignited by the spark plug and creates the power stroke.

An engine intake system equipped with a high performance air filter which is cone shaped to increase air flow. The intake is on the right side in this picture, the intake manifold having the ridges and the throttle body is connected to the rubber hose that links to the cone filter. The airflow sensor is the plug on top of the tube leading to the cone filter.

The next system is the exhaust system. It consists of the exhaust manifold (also called headers), pipe, oxygen sensor, catalytic converter, muffler/silencer and the tailpipe(s). Starting at the engine is the manifold. It essentially directs the exhaust gasses away from the engine down the pipe, towards the back of the car. It is bolted to the rest of the pipe. There is a gasket around the manifold designed to keep the expanding gasses focused towards the back and air tight. The pipe is sort of a general term referring to the set of welded tubes that directs the exhaust gasses. These pipes are usually made up of several pieces, welded together at different points. The pipe is curved to allow space for other stuff under the car and to reduce the energy of the gasses, making them quieter and easier to regulate. The oxygen sensor (also called the O2 or Lambda sensor) is responsible for monitoring the fuel mixture in the exhaust system and is linked to the car's ECU (engine control unit). It detects a rich or lean mixture and it generates voltage from the gasses making contact with the sensor's probe, which is checked by the ECU and it will adjust the fuel ratio accordingly to compensate. If the lambda sensor fails or is removed then the ECU has no way to monitor the fuel mixture ratio and has to guess the fuel mixture which makes the engine speed fluctuate, running roughly and using excessive amounts of fuel. A catalytic converter functions to reduce emissions from exhaust gasses in order to be more friendly to the environment and conform to emissions standards. It is essentially a section of the exhaust that serves as a catalyst, that catalyst is made with platinum and palladium. These two metals are able to convert carbon monoxide into carbon dioxide which is significantly less harmful and more environmentally friendly. Catalytic converters are usually located near the middle of the exhaust system so that the carbon monoxide will pass through the catalyst before it is too late to convert the majority of the carbon monoxide into dioxide, and looks like a lump in the pipe. The muffler is designed to make the exhaust sound more quiet. The way that a muffler silences the exhaust gasses is by bouncing them back and forth which decreases the energy of the gas, making it quieter. This sound deflection is achieved by using two pipes inside of the muffler/silencer that act to cause the exhaust gasses to interfere with each other as they bounce back and forth inside of the chamber. As they interfere with one another the energy of the sound waves is drastically decreased by the time the gasses escape the pipe. Over time mufflers/silencers wear out and oftentimes corrode and then holes are formed which makes the gasses leak and be very noisy, so over time the muffler should be replaced. And the tailpipe is connected directly to the muffler/silencer. It is simply the end of the exhaust cycle and is the last part the gasses go through.

The exhaust system from a BMW E60 M5. From front to back:

Headers (manifolds), pipes, catalytic converter (two of them

in this case), the oxygen sensor has been removed from this,

but it would be inserted into the pipes between the headers

and catalytic converters screwed into the piping. And at the

end are the mufflers (with two tailpipes each, not visible here).

The next parts to be explained are the fuel system components. This system consists of the fuel tank, fuel filter, fuel line, fuel rail, and the fuel injectors. All modern cars use fuel injection versus a carburetor like old cars use. The fuel tank stores the fuel that the car burns to make energy, they are typically located at the rear of the car. With cars that are really old and have sat for a while without use, the gas tank can get rusty and over time sediment can get into the tank and sink to the bottom of the tank which What links to the fuel tank is the fuel line that sucks the fuel out of the tank up to the engine to be burned and used. The pump is what forces the fuel across the fuel line into each cylinder. The fuel filter serves the same purpose that the air filter does and that is to remove debris and dirt from the fuel before it is injected into the engine. The filter must occasionally be replaced because the buildup of debris blocks it from the fuel line. The fuel rail is what links all of the injectors to the fuel line and into the cylinders so that the fuel goes from the tank across the line across the rails and evenly distributed to each injector and then into each cylinder. And the fuel injectors put the gas into the cylinders where it is mixed with air, compressed and ignited to create power. Over time the injectors get dirty and buildup coats them necessitating replacement or cleaning. All of these parts ensure that there is combustible fuel in the cylinder to mix with the air and ignite to create power. All of these are linked to the ECU (electronic control unit) to regulate factors like fuel pressure, fuel mixture, and injection timing.

Next up is the ignition system. This system is responsible for regulating the process of igniting the fuel/air mixture in each cylinder. It consists entirely of electrical components: the ignition key, starter motor, distributor (nowadays just ignition coil on plug), ignition coil packs and the spark plugs. What happens when your turn the key to fire up your car? A lot actually! First is the key. This is what activates the whole ignition process when you turn it. The starter is an electric motor that turns the engine over in order to start the combustion. It is activated by an electric current that goes to the engine control unit, through the neutral safety switch (which prevents an overloaded current from damaging the electrical system), to the switch clutch and then to the solenoid. The bendix is pushed out which engages the starter gear and turns the flywheel, which is connected to the crankshaft and the engine can be spun. The distributor takes the electric charge and distributes it to the coil packs and past the spark plugs into the cylinder. Almost all cars built within that past 10 years or so are distributor less and instead of this system, they have one ignition coil per spark plug to decrease the number of moving components which fail sooner. This newer system is called Coil-On-Plug which individually feeds current into each spark plug. This is preferred because instead of using the more complex distributor which relies on moving parts, it has no moving parts which lasts longer.The ignition coils (or coil packs) serve to carry the electric charge to the spark plugs, and are connected to the distributor by wires. And the spark plugs carry electricity between 40,000 and 100,000 volts into the combustion chamber that is to ignite the air/fuel mixture spayed in my the fuel injectors and taken in by the induction system. Without spark plugs, the engine would not run. Tune-ups of the ignition system are very important, as spark plugs wear out and coil packs burn up after a while of usage. All of these ignition systems run off of current from the battery, which is why the battery must be properly charged in order for the car to run. And one additional part that is vital for the ignition system to work is the alternator. It essentially maintains battery charge while the car is running and will very slowly replenish a small loss of charge. The alternator works by a pulley attached to the engine that is connected by a belt (called a serpentine belt). This pulley/belt combination spins the pulley wheel on the alternator and it converts this mechanical energy of spinning into electricity which is fed to the battery.

A starter motor. The end sticking out is the bendix,

which is what links the starter gears with the flywheel

gears in order to spin the engine

A distributor (only used with some engines & older systems)

its usage of moving parts makes it fail more easily than COP

(coil on plug) systems used nowadays

An ignition coil (for most modern applications), used

for each individual spark plug. The rubber connecting

sleeve on the end has a metal core inside it that conducts

the electric current into the spark plug

A set of spark plugs. Most are made with copper

or platinum but newer developments use iridium

An alternator; the black wheel on the side is the pulley

that links to the belt

The lubrication system is what keeps the moving parts of the engine from damaging each other by providing a film of oil between the moving surfaces of the engine. If it were not for this lubrication then the engine would grind and wear itself down so badly that it would seize from the friction (friction creates heat which eventually could weld the metal together inside, called an engine seize). This lubrication system consists of the oil, oil pan, pickup tube, oil filter, and the oil pump. Starting things off is the oil itself. It functions to provide a film that the moving metal parts slide across to avoid grinding damage. There are many different grades of viscosity and weight for motor oil (for example 5W-30 has a weight rating of 5 and a viscosity of 30). There are generally 3 different types of oil: conventional (mineral), synthetic and synthetic blend (has a conventional base with many synthetic additives). The oil pan (also called the sump) is what stores all of this lubricating oil while the engine is powered off, like a reservoir. This is located underneath the engine crankcase. Next, the pickup tube is the vital because the oil is needed the instant the engine is started. When u turn the key, the oil gets sucked up through this tube. What is responsible for this sucking action is the oil pump and it needs to go against gravity in order to get the oil up out from the pan beneath the engine to where it needs to be! Before the oil is allowed to be spread throughout the engine it goes through the filter which stops any dirt and debris from getting through (that's why they gotta get replaced with every oil change because the buildup prevents it from doing its job). The inside of the engine has many small holes and ports that allow the oil in to coat and lubricate the bearings. And after the oil goes through most of it ends up down in the pan, ready for the cycle to begin again over and over. Some oil stays coated on the metal but not enough to safely run, hence the need for the cycle to repeat.

This is an oil pan (or sump). The copper bolt on the end is the

drain plug. This allows u to drain the old dirty oil

out of it (an oil change)

Oil being poured into an engine. Fresh oil is a golden honey

color

An oil checking diagram. Keep your oil levels up, and clean!

Das oil pump

Oil filter- cartridge type

Oil filter- screw on container type

The cooling system is important to keep the engine from overheating and sustaining heat damage. It consists of the radiator, antifreeze/coolant, radiator fan, coolant hoses, thermostat, water pump, expansion tank and the pressure cap. All of these parts function to circulate antifreeze throughout the engine and to cool it down. The antifreeze/coolant serves to cool the metal inside the engine. It achieves this by using heat transfer, which it does by absorbing the heat from the metal and to hold it while it gets pumped away from the engine which causes the engine heat to be maintained. Coolant is made up of a chemical mixture of ethylene glycol and distilled water, as well as dyes in order to differentiate the different types. This mixture ensures maximum heat dissipation and cooling ability. Many coolants nowadays contain phosphates (to prevent blockage and build up within the cooling system) and nitrates (to neutralize the phosphates). However some manufacturers have stopped using phosphates and nitrates (like BMW, Mercedes-Benz, Audi/Volkswagen) because in engines with aluminum alloy are at increased risk of corrosion from the nitrates and phosphates. Most antifreeze is green but there is blue, pink, clear, and even yellow coolant as well. Different manufacturers use certain grade/color coolant. For example, BMW uses blue antifreeze that is phosphate-free because they use aluminum cylinder heads w/ iron blocks/aluminum blocks, and normal coolant is too corrosive. It usually lasts a long while but it is recommended that you flush it periodically. It travels through the coolant hoses which directs it from the tank & radiator into the engine block through the water jackets. Coolant hoses serve as passageways for the antifreeze to travel from the radiator to the engine block. They are held in place by clamps. . A thermostat in a car is what senses the temperature inside of the cooling system. It is made up of a chamber containing a wax pallet that melts and expands at certain temperature intervals and it connected to a valve that opens and closes the coolant flow stream. IT alternates based on temperature which allows it to control the cooling system accurately enough to maintain an engine temperature. An automotive water pump serves to pump the antifreeze through the system.This pump is driven by the serpentine belt or in some cases the timing belt that is attached to the camshaft(s). The radiator is used to cool the antifreeze as soon as it leaves the engine block (when it leaves the block it is very hot lol). It is made up of thin aluminum fins that act to transfer the heat out of the coolant as it cycles through the fins. The radiator fan is the next step in cooling the antifreeze. It prevents the radiator from overloading of heat by blowing air onto it. This fan is controlled by a switch and a relay, and are automatically activated. An expansion tank is basically the coolant reservoir and holds the antifreeze. And on top of this tank is the pressure cap, which functions to seal the heat inside of the tank and prevent it from leaking. It has a seal that keeps heat in, and it is NEVER a good idea to open it while the engine is warm.

Some antifreeze being poured into the engine reservoir

An automotive water pump

This is a model of an automotive cooling system

Now we will move on to the internal components of an engine, what goes on inside. The inside of an engine is pretty straightforward: the valves, camshaft(s), cylinder head, timing chain/belt, pistons, connecting rods, crankshaft, flywheel, and the engine block. In order for the engine to work, combustion is needed. This is achieved by fuel and air entering the cylinders. And the parts that let the air and fuel in to combust are the valves. They open and close according to the engine speed (the faster the engine is going the faster the valves open and close). There are two types of valves: the intake and exhaust. The intake lets air in to mix with the fuel from the fuel injectors, and the exhaust lets out the product of combustion, which are explosive gasses. Attached to valves are the valve springs which make it possible for them to open and close as fast as they do. The camshaft is what causes the valves to open and close. Along the camshaft are lobes that spin with the crankshaft and these lobes click down on the valves which make them open and when the lobe faces up then the springs retract which makes it move up, closing the valve. What causes the camshaft to move is the timing chain/belt. That is linked to the crankshaft pulley and there are gears on the end of the camshaft that mesh with the chain/belt. With a chain, the timing device is a multi link chain which meshes with the gears and pulley, but with a belt system, it is a Kevlar belt with grooves that allow it to mesh with the camshaft gear and the crankshaft pulley. The cylinder head holds the valves and camshaft and is bolted on top of the block on top of the head gasket which seals the combustion chamber from coolant. The cylinder block holds the crankshaft, pistons and conrods within it Another component vital to combustion are the pistons. Remember the four strokes of an internal combustion engine (Intake, compression, power, and exhaust)? Well the pistons are responsible for compressing the fuel/air mixture which is what gives the combustion power. The heads of the pistons are specially machined to create ideal compression for different types of engines. They are forged independently in order to shape them for a proper fit. Engine connecting rods are essentially what link the pistons to the crankshaft. They each have "wrist pins" which connect the piston to the conrod and they allow the rod to move back and forth without moving the piston within the cylinder. And the bottom of the connecting rod has two bolts that are connected to the crankshaft. Now moving onto the crankshaft. This important component is the center of the rotation within an engine. It essentially converts the linear up-and-down motion of the pistons within their cylinders into the rotational motion which must be transmitted to the drive wheels (via the drive train) in order to make them spin. The distance between the conrods on the crankshaft is important for proper engine balance and to prevent metal stress/overload and it is called the connecting rod journal. Most engines also have counterweights on the crank that provide weight-canceling properties that make the engine properly balanced. As one set of weights move up the others are down which cancels out vibration that could stress the engine. The flywheel is super important to maintaining rotation when there is no power stroke. It does this by storing energy within the wheel that it gains by resisting fluctuations in engine rotation speed. It stores up the rotational inertia and provides that kinetic energy to keep the engine moving between strokes when no power is being generated. The flywheel is also one of the key components used to start the engine (the flywheel is linked to the starter gear/motor and bendix).