Fuel Systems

Free Web Hosting Provider - Web Hosting - E-commerce - High Speed Internet - Free Web Page

The purpose of the fuel system is to provide a mixture of fuel and air to the engine of the car. The air-fuel mixture must be in proportion to the speed and load placed on the engine. Major parts of the system include: fuel tank and cap, emission controls, fuel line, fuel pump, fuel filter, carburetor, and intake manifold as well as the fuel gauge, which indicates the amount of fuel in the tank.

Engine fuel is mainly made up of hydrogen and carbon, mixed so that it will burn with oxygen present, and will free its heat energy into mechanical energy. Liquid fuels are ideal for internal combustion engines, because they can be economically produced, have a high heat value per pound, an ideal rate of burning, and can be easily handled and stored. The most common engine fuels are gasoline, kerosene and Diesel fuel oil.

Gasoline has many advantages and is used to a greater extent than any other fuel in internal combustion engines having spark ignition. It has a better burning rate than other fuels, and, because it vaporizes easily, it gives quick starting in cold weather, smooth acceleration and maximum power.

Diesel fuel oil ranks next to gasoline in quantity used. It can be produced as cheaply as gasoline, but its use is limited to Diesel type engines. The use of kerosene as a fuel is usually limited to farm tractors, marine and stationary engines, all which operate at a fairly constant speed. Its traits are such that it cannot be properly mixed with air and controlled in variable speed engines.

A gasoline's ability to resist detonation is called its "octane" or anti-knock rating. Gasoline from asphaltic base crude oil produces less knock than one from paraffinic base crude. Cracked gas has less tendency to knock than straight run gas. All marketed gasolines are a blend of straight run and cracked gasolines, so unless their blending is controlled, the anti-knock qualities will vary.

A mixture of iso-octane, which has a very high anti-knock rating, and heptane, which makes a pronounced knock, is used as a reference fuel to establish an anti-knock standard. The anti-knock value or octane number is represented by the percentage of volume of iso-octane that must be mixed with normal heptane in order to duplicate the knocking of the gasoline which is being tested. These ratings range from 50 in third grade gasolines to 110 in aviational fuels. The rating of 100 means a fuel having an anti-knock value equal to that of iso-octane. If the octane rating of a gasoline is naturally low, the fuel will detonate as it burns and power will be applied to the pistons in hammer-like blows. The ideal power is that which pushes steadily on the pistons, rather than hammer against them. The octane rating of a gasoline can be raised by treating it with a chemical which is not a fuel. The best chemical known is tetra-ethyl lead compound, which is added to the gasoline.

Tetra-ethyl lead is a liquid which mixes thoroughly with gasoline and vaporizes completely. Ethylene dibromide prevents the tetra-ethyl lead from forming lead oxide deposits on spark plugs and on valve seats and stems. Red dye is added to identify an ethyl treated gasoline and to warn against its being used as anything but an engine fuel. In 1975, it became illegal to use a leaded gasoline except in cars built prior to this time. With the addition of the catalytic converter, it is undesirable to burn leaded fuel, because leaded fuel will clog the converter and increase the back-pressure of the exhaust.

All modern fuel systems are fed through a pump, so the fuel tank is usually at the rear of the chassis under the trunk compartment. Some vehicles have a rear engine with the tank in the forward compartment. The fuel tank stores the excess fuel until it is needed for operation of the vehicle. The fuel tank has an inlet pipe and an outlet pipe. The outlet pipe has a fitting for fuel line connection and may be located in the top or in the side of the tank. The lower end is about one-half inch above the bottom of the tank so that collected sediment will not be flushed out into the carburetor. The bottom of the tank contains a drain plug so that tank may be drained and cleaned.

The gas tank of the early cars was placed higher than the engine. The idea was that the gas would flow down to the engine. This arrangement caused a problem when the car went uphill -- the gas flowed away from the engine. Solution: drive up the hill backwards!

Clean fuel is important, because of the many small jets and passages in the carburetor and openings in a fuel injector. To ensure this cleanliness, fuel filters are installed in the fuel line. Fuel filters can be located at any point between the fuel tank and the carburetor. One may be in the tank itself, in the fuel pump or in the carburetor. The most common placement is between the fuel tank and a mechanical fuel pump. In this case, the fuel enters a glass bowl and passes up through the filter screen and out through an outlet. Any water or solid material which is trapped by the filter will fall to the bottom of the glass bowl where it can be easily seen and removed. Dirt particles usually come from scales of rust in the tank cars, storage tanks or drums. Water comes from condensed moisture in the fuel tanks.

The fuel pump has three functions: to deliver enough fuel to supply the requirements of an engine under all operating conditions, to maintain enough pressure in the line between the carburetor and the pump to keep the fuel from boiling, and to prevent vapor lock. Excessive pressure can hold the carburetor float needle off its seat, causing high gasoline level in the float chamber. This will result in high gasoline consumption. The pump generally delivers a minimum of ten gallons of gasoline per hour at top engine speeds, under an operating pressure of from about 2 1/2 to 7 pounds. Highest pressure occurs at idling speed and the lowest at top speed. Although fuel pumps all work to produce the same effect, there are various types that may operate somewhat differently.

The mechanical fuel pump differs in that it has a vacuum booster section. The vacuum section is operated by the fuel pump arm; otherwise, it has nothing to do with the fuel system. During the suction (or first) stroke, the rotation of the eccentric on the camshaft puts the pump operating arm into motion, pulling the lever and diaphragm down against the pressure of the diaphragm spring and producing suction (vacuum) in the pump chamber. The suction will hold the outlet valve closed and pull the inlet valve open, causing fuel to flow through the filter screen and down through the inlet valve of the pump chamber.

During the return stroke, the diaphragm is forced up by the diaphragm spring, the inlet valve closes and the outlet valve opens to allow fuel to flow through the outlet to the carburetor. The operating lever is hinged to the pump arm, so that it can move down but cannot be raised by the pump arm. The pump arm spring forces the arm to follow the cam without moving the lever. The lever can only be moved upward by the diaphragm spring. This process causes fuel to be delivered to the carburetor only when the fuel pressure in the outlet is less than the pressure maintained by the diaphragm spring. This happens when the passage of fuel from the pump into the carburetor float chamber is open and the float needle is not seated.

Electric fuel pumps have been used for many years on trucks, buses and heavy equipment, and they have also been used as replacements for mechanically operated fuel pumps on automobiles, but only recently have they become part of a car's original equipment. The replacement types usually use a diaphragm arrangement like the mechanical pumps, except that it is actuated by an electrical solenoid.

The electrically driven turbine type of pump, first used on the Buick Riviera, was a great departure from the usual fuel pump design. It uses a small turbine wheel driven by a constant speed electric motor. The entire unit is located in the fuel tank and submerged in the fuel itself. This pump operates continuously when the engine is running. It keeps up a constant pressure which is capable of supplying the maximum fuel demands of the engine. When less fuel is required, the pump does not deliver at full potential, because the turbine is not a positive displacement type like the mechanical pump. Consequently, the turbine will run without pumping fuel and so, needs no means of varying fuel delivery rate like its mechanical counterpart. Since the fuel can flow past the spinning turbine blades, there is no need for pump inlet and outlet valves nor is there any need to vary its speed.

A relay for the electric fuel pump is used to complete the circuit to the fuel pump. This cuts off current to the fuel pump in the event of an accident.

Several fuel pumps have a vacuum booster section that operates the windshield wipers at an almost constant speed. The fuel section then functions in the same way as ordinary fuel pumps. One difference is that the rotation of the camshaft eccentric in the vacuum pump also operates the vacuum booster section by actuating the pump arm, which pushes a link and the bellows diaphragm assembly upward, expelling air in the upper chamber through its exhaust valve out into the intake manifold. On the return stroke of the pump arm, the diaphragm spring moves the bellows diaphragm down, producing a suction in the vacuum chamber. The suction opens the intake valve of the vacuum section and draws air through the inlet pipe from the windshield wipers.

When the wipers are not operating, the intake manifold suction (vacuum) holds the diaphragm up against the diaphragm spring pressure so that the diaphragm does not function with every stroke of the pump arm. When the vacuum is greater than the suction produced by the pump, the air flows from the windshield wiper through the inlet valve and vacuum chamber of the pump and out the exhaust valve outlet to the manifold, leaving the vacuum section inoperative. With high suction in the intake manifold, the operation of the wiper will be the same as if the pump were not installed. When the suction is low, as when the engine is accelerated or operating at high speed, the suction of the pump is greater than that in the manifold and the vacuum section operates the wipers at a constant speed. Some pumps have the vacuum section located in the bottom of the pump instead of in the top, but the operation is basically the same.

Air cleaners are made to separate dust and other particles in the incoming air before it enters the carburetor. Thousands of cubic feet of air are drawn from within the car hood and passed through the engine cylinders, so it is important that the air is clean.

When driving on dirt or other dusty roads, dust particles are drawn through the radiator and find their way into the engine if it is not filtered and cleaned. Dust and other foreign materials in the engine will cause excessive wear and operating problems.

Cars are equipped with fuel gauges which are operated along with the vehicle's electrical system. There are two types: the thermostatic type and the balancing coil type. The thermostatic type is made of a standing unit, located in the fuel tank, and the gauge itself (registering unit), which is located on the instrument panel. The fuel gauge used in some cars and trucks is of the electrically operated balanced coil type. These have a dash unit and a tank unit. The dash unit has two coils, spaced about 90 degrees apart, with an armature and integral pointer at the intersections of the coil axis. The dial has a scale in fractions between "Empty" and "Full". The tank unit has a housing, which encloses a rheostat, and a sliding brush which contacts the rheostat. The brush is actuated by the float arm. The movement of the float arm is controlled by the height of the fuel in the supply tank. The height of the fuel (called variations in resistance) changes the value of the dash unit coil so that the pointer indicates the amount of fuel available. A calibrated friction brake is included in the tank unit to prevent the wave motions of the fuel from fluctuating the pointer on the dash unit. Current from the battery passes through the limiting coil to the common connection between the two coils, which is the lower terminal on the dash unit. The current is then offered two paths, one through the operating coil of the dash unit and the other over the wire to the tank unit. When the tank is low or empty, the sliding brush cuts out all resistance in the tank unit. Most of the current will pass through the tank unit circuit because of the low resistance and only a small portion through the operating coil to the dash unit. As a result, this coil is not magnetized enough to move the dash unit pointer, which is then held at the "Empty" position by the limiting coil.

If the tank is partly full or full, the float rises on the surface of the fuel and moves the sliding brush over the rheostat, putting resistance in the tank unit circuit. More current will then pass through the operating coil to give a magnetic pull on the pointer, which overcomes some of the pull of the limiting coil. When the tank is full, the tank unit circuit contains the maximum resistance to the flow of the current. The operating coil will then receive its maximum current and exert pull of the pointer to give a "Full" reading. As the tank empties, the operating coil loses some of its magnetic pull and the limiting coil will still have about the same pull so that the pointer is pulled toward the lower reading. Variations in battery voltage will not cause an error in the gauge reading because its operation only depends on the difference in magnetic effect between the two coils.

Fuel lines, which connect all the units of the fuel system, are usually made of rolled steel or, sometimes, of drawn copper. Steel tubing, when used for fuel lines, is generally rust proofed by being copper or zinc plated.

Fuel lines are placed as far away from exhaust pipes, mufflers, and manifolds as possible, so that excessive heat will not cause vapor lock. They are attached to the frame, the engine, and other units in such a way that the effect of vibration is minimal, and so that they are free of contact with sharp edges which might cause wear. In areas where there is a lot of movement, as between the car`s frame and rubber-mounted engine, short lengths of gasoline resistant flexible tubing are used.

An intake manifold is a system of passages which conduct the fuel mixture from the carburetor to the intake valves of the engine. Manifold design has much to do with the efficient operation of an engine. For smooth and even operation, the fuel charge taken into each cylinder should be of the same strength and quality.

Distribution of the fuel should, therefore, be as even as possible. This depends greatly upon the design of the intake manifold. Dry fuel vapor is an ideal form of fuel charge, but present-day fuel prevents this unless the mixture is subjected to high temperature. If the fuel charge is heated too highly, the power of the engine is reduced because the heat expands the fuel charge. Therefore, it is better to have some of the fuel deposited on the walls of the cylinders and manifold vents. Manifolds in modern engines are designed so that the amount of fuel condensing on the intake manifold walls is reduced to a minimum.

In a V-8 engine, the intake manifold is mounted between the cylinder heads. The L-head engine's manifold is bolted to the side of the block, and the I-head manifold is bolted to the cylinder head.

The ram induction manifold system consists of twin air cleaners, twin four-barrel carburetors and two manifolds containing eight long tubes of equal length (four for each manifold).

This system was designed by the Chrysler Company to increase power output by in the middle speed range (1800-3600 rpm). Each manifold supplies one bank of cylinders and is carefully calculated to harness the natural supercharging effect of a ram induction system. By taking advantage of the pulsations in the air intake column caused by the valves opening and closing, sonic impulses help pack more mixture into the combustion chambers.

In the Chrysler system, the air-fuel mixture from each carburetor flows into a chamber directly below the carburetor, then passes through the long individual intake branches to the opposite cylinder bank. The right-hand carburetor supplies the air-fuel mixtures for the left-hand cylinder bank, and the left-hand carburetor supplies the right cylinder bank. The passages between the manifolds are interconnected with a pressure equalizer tube to maintain balance of the engine pulsations.

Most engines have automatically operated heat controls which use the exhaust gases of the engine to heat the incoming fuel-air charge during starting and warm-up. This improves vaporization and mixture distribution. When the engine is cold, all of the exhaust gas is deflected to and around the intake manifold "hot spot". As the engine warms up, the thermostatic spring is heated and loses tension. This allows the counterweight to change the position of the heat control valve gradually so that, at higher driving speeds with a thoroughly warmed engine, the exhaust gases are passed directly to the exhaust pipe and muffler.

In the ram induction system, there is a heat control chamber in each manifold to operate the automatic choke and to heat the fuel mixture after warm-up. A heat control valve in each exhaust manifold will by-pass the exhaust gas through an elbow to the intake manifold heat control chamber. Heat outlet pipes then carry the gas down to the "Y" connector under the heat control valve.

Heat control is regulated by a coiled thermostatic spring mounted on the exhaust manifold. A counterweight is mounted on the other end of the heat control valve shaft and this counterweight, in conjunction with the thermostatic spring, operates to close and open the heat control valve.

The purpose of the carburetor is to supply and meter the mixture of fuel vapor and air in relation to the load and speed of the engine. Because of engine temperature, speed, and load, perfect carburetion is very hard to obtain.

The carburetor supplies a small amount of a very rich fuel mixture when the engine is cold and running at idle. With the throttle plate closed and air from the air cleaner limited by the closed choke plate, engine suction is amplified at the idle-circuit nozzle. This vacuum draws a thick spray of gasoline through the nozzle from the full float bowl, whose fuel line is closed by the float-supported needle valve. More fuel is provided when the gas pedal is depressed for acceleration. The pedal linkage opens the throttle plate and the choke plate to send air rushing through the barrel. The linkage also depresses the accelerator pump, providing added gasoline through the accelerator-circuit nozzle. As air passes through the narrow center of the barrel, called the "venturi", it produces suction that draws spray from the cruising-circuit nozzle. The float-bowl level drops and causes the float to tip and the needle valve to open the fuel line.

To cause a liquid to flow, there must be a high pressure area (which in this case is atmospheric pressure) and a low pressure area. Low pressure is less than atmospheric pressure. The average person refers to a low pressure area as a vacuum. Since the atmospheric pressure is already present, a low pressure area can be created by air or liquid flowing through a venturi. The downward motion of the piston also creates a low pressure area, so air and gasoline are drawn through the carburetor and into the engine by suction created as the piston moves down, creating a partial vacuum in the cylinder. Differences between low pressure within the cylinder and atmospheric pressure outside of the carburetor causes air and fuel to flow into the cylinder from the carburetor.

A supercharger is a compressor. Hence, a supercharged engine has a higher overall compression than a nonsupercharrged engine having the same combustion chamber volume and piston displacement and will burn more fuel. Unfortunately, the increase in power is not proportional to the increase in fuel consumption. There are two general models of superchargers, the Rootes type and the centrifugal type. The Rootes "blower" has two rotors, while the centrifugal uses an impeller rotating at high speed inside a housing.

Superchargers can be placed between the throttle body of the carburetor or fuel injection system and the manifold; or at the air inlet before the throttle body. Racing cars usually have it located between the throttle body and the manifold. This design has the advantage that the fuel can be supplied through the throttle body without modification to any part of the system. If the supercharger is placed in front of the throttle body, fuel must be supplied under sufficient pressure to overcome the added air pressure created by the supercharger. The advantage of a supercharger over a turbocharger is that there is no lag time of boost; the moment the accelerator pedal is depressed, the boost is increased.

A turbocharger, or supercharger, can boost engine power up to 40%. The idea is to force the delivery of more air-fuel mixture to the cylinders and get more power from the engine. A turbocharger is a supercharger that operates on exhaust gas from the engine.

Although turbochargers and superchargers perform the same function, the turbocharger is driven by exhaust gases, while the supercharger is driven by belts and gears. The turbocharger has a turbine and a compressor, and requires less power to be driven than a supercharger. The pressure of the hot exhaust gases cause the turbine to spin. Since the turbine is mounted on the same shaft as the compressor, the compressor is forced to spin at the same time, drawing 50% more air into the cylinders than is drawn in without the turbocharger. This creates more power when the air-fuel mixture explodes.

A turbocharged engine's compression ratio must be lowered by using a lower compression piston, since an excessive amount of pressure will wear on the piston, connecting rods, and crankshaft, and destroy the engine. All of these parts then, as well as the transmission, must be strengthened on a turbocharged engine or it will be torn apart by the increased horsepower.

The breather is the positive crankcase ventilation system directing atmospheric pressure to the crankcase. The atmospheric pressure then pushes the blowby gases to a low pressure area. The air that is directed into the crankcase must first be filtered; if it is not, the dust and sand particles will destroy the engine parts. When there is too much blowby, it is routed back through the crankcase breather element. It then enters the carburetor or throttle body with the incoming fresh air to be burned in the cylinders. In addition, the breather helps to keep the regular air filter cleaner for a longer period of time, since blowby contains oil vapor from the crankcase.

Fuel in the carburetor must be maintained at a certain level under all operating conditions; this is the function of the float circuit. The needed fuel level is maintained by the float. When its attached lever forces the needle valve closed, the flow of fuel from the pump is stopped. As soon as fuel is discharged from the float bowl, the float drops. The needle valve opens and fuel flows into the bowl again. In this way, the fuel is level to the opening of the main discharge nozzle. The float level must be set with a high degree of accuracy. If the level is too low, not enough fuel will be supplied to the system and the engine will stall on turns; if the level is too high, too much fuel will flow from the nozzle.

A metering rod varies the size of the carburetor jet opening. Fuel from the float bowl is metered through the jet and the metering rod within it. The fuel is forced from the jet to the nozzle extending into the venturi. As the throttle valve is opened, its linkage raises the metering rod from the jet. The rod has several steps, or tapers, on the lower end. As it is raised in the jet, it makes the opening of the jet greater in size. This allows more fuel to flow through the jet to the discharge nozzle. The metering must keep pace with the slightest change in the throttle valve position so that the correct air-fuel mixture is obtained in spite of engine speed.

Chokes perform the fuel mixture adjustments necessary to start a cold engine. When the fuel-air mixture is too cold, the engine won't start properly, or will stall out periodically. The choke when engaged (closed) the choke causes the fuel air mixture to be increased, or "enriched". The choke is a special valve placed at the mouth of the carburetor so that it partially blocks off the entering air. When the choke plate closes, the vacuum below it increases, drawing more fuel from the fuel bowl. The rich fuel mixture burns even at lower temperatures, allowing the engine to warm up.

The manual choke is a knob on the dash, usually the push-pull type, which extends from the choke on the carburetor to the instrument panel. The driver closes the choke when starting the engine. The main thing to know about a manual choke is to push it back in when the engine has reached normal operating temperature. The trouble with the manual choke is that the driver often forgets to open it fully. This results in a rich fuel mixture which causes carbon to form in the combustion chambers and on the spark plugs. To correct this problem, the automatic choke was developed.

The automatic choke relies on engine heat. The choke valve is run by a thermostat which is controlled by exhaust heat. When the engine is cold, the valve will be closed for starting. As the engine warms, the exhaust heat will gradually open the choke valve. An automatic choke depends on a thermostatic coil spring unwinding as heat is supplied. As the engine warms up, manifold heat is transmitted to the choke housing. The heat causes the bimetal spring to relax, opening the valve.

An electric heating coil in the automatic choke shortens the length of time that the choke valve is closed. As the spring unwinds, it causes the choke valve in the carburetor air horn to open. This lets more air pass into the carburetor. The coil is mounted in a well in the exhaust crossover passage of the intake manifold. Movement of the bimetal spring is relayed to the choke valve shaft by means of linkage and levers.

The carburetor, despite all it advances: air bleeds, correction jets, acceleration pumps, emulsion tubes, choke mechanisms, etc., is still a compromise. The limitations of carburetor design is helping to push the industry toward fuel injection.

Direct fuel injection means that the fuel is sprayed directly into the combustion chamber. The fuel injected nozzle is located in the combustion chamber.

Throttle Body injection systems locate the injector(s) within the air intake cavity, or "throttle body". Multi-point systems use one injector per cylinder, and usually locate the injectors at the mouth of the intake port.

The fuel injector is an electromechanical device that sprays and atomizes the fuel. The fuel injector is nothing more than a solenoid through which gasoline is metered. When electric current is applied to the injector coil, a magnetic field is created, which causes the armature to move upward. This action pulls a spring-loaded ball or "pintle valve" off its seat. Then, fuel under pressure can flow out of the injector nozzle. The shape of the pintle valve causes the fuel to be sprayed in a cone-shaped pattern. When the injector is de-energized, the spring pushes the ball onto its seat, stopping the flow of fuel.

Mechanical fuel injection is the oldest of the fuel injection systems. It uses a throttle linkage and a governor. It is now used mainly on diesel engines. Hydraulic fuel injection is used by some of the imports. Hydraulic pressure is applied to a fuel distributor as a switching device to route fuel to a specific injector. The fuel from the tank is carried under pressure to the fuel injector(s) by an electric fuel pump, which is located in or near the fuel tank. All excess is returned to the fuel tank.

The principle of electronic fuel injection is very simple. Injectors are opened not by the pressure of the fuel in the delivery lines, but by solenoids operated by an electronic control unit. Since the fuel has no resistance to overcome, other than insignificant friction losses, the pump pressure can be set at very low values, consistent with the limits of obtaining full atomization with the type of injectors used. The amount of fuel to be injected is determined by the control unit on the basis of information fed into it about the engine's operating conditions. This information will include manifold pressure, accelerator enrichment, cold-start requirements, idling conditions, outside temperature and barometric pressure. The systems work with constant pressure and with "variable timed" or "continuous flow" injection. Compared with mechanical injection systems, the electronic fuel injection has an impressive set of advantages. It has fewer moving parts, no need for ultra-precise machining standards, quieter operation, less power loss, a low electrical requirement, no need for special pump drives, no critical fuel filtration requirements, no surges or pulsations in the fuel line and finally, the clincher for many car makers, lower cost.

All gasoline engines have a throttle valve to control the volume of intake air. The amount of fuel and air that goes into the combustion chamber regulates the engine speed and, therefore, engine power. The throttle valve is linked to the accelerator (gas pedal). The throttle valve is a butterfly valve that usually consists of a disc mounted on a spindle. The disc is roughly circular, and it has the same diameter as the main air passage in the throat or "venturi". In a carburetor, the throttle valve is usually located at the bottom of the carburetor, between the jet nozzle and the intake manifold. The throttle spindle is connected to the accelerator in such a manner that when the pedal is depressed, the valve opens. When the pedal is released, the valve closes. Fuel injected engines use throttle valves to regulate engine power, even though the fuel is also regulated through the injectors.

The fuel delivery in a carburetor tends to lag behind the motion of the throttle. The basic carburetor operates when the throttle valve is fully open or partially open, but not when it's closed. No driver wants the engine to stop every time the foot leaves the accelerator; such a car would be tiring and stressful to drive, even in the best of road conditions, let alone in a traffic situation. To keep the engine running smoothly and evenly when no power is needed, the idle circuit was added inside the carburetor. The idle jet admits fuel on the engine side of the throttle valve. Additional air is mixed with this fuel through an air bleed. The result is an entirely separate carburetor circuit which operates only when the throttle valve is closed.

"Barrel" is a popular term for the carburetor throat. There is one venturi in each throat. A two-barrel carburetor has a primary venturi for part-load running and a secondary venturi for full-throttle; a four-barrel carburetor has two primary and two secondary venturis. The venturi tube is important in carburetion. A "venturi" is a tube with a restricted section. When liquid or air passes through the venturi tube, the speed of flow is increased at the restriction, and air pressure is decreased, creating an "increase in vacuum" (a reduction in ambient pressure). This causes fuel to be drawn into the barrel. The venturi action is used to keep the correct air-fuel ratio throughout the range of speeds and loads of the engine.

The delay between the time the fuel is injected into the cylinder and ignition is expressed as a cetane number. Usually, this is between 30 and 60. Fuels that ignite rapidly have high cetane ratings, while slow-to-ignite fuels have lower cetane ratings. A fuel with a better ignition quality would help combustion more than a lower cetane fuel during starting and idling conditions when compression temperatures are cooler. Ether, with a very high cetane rating of 85-96, is often used for starting diesel engines in cold weather. The lower the temperature of the surrounding air, the greater the need for fuel that will ignite rapidly. When the cetane number is too low, it may cause difficult starting, engine knock, and puffs of white exhaust smoke, especially during engine warm-up and light load operation. If these conditions continue, harmful engine deposits will accumulate in the combustion chamber.

Pressurized cans of starter fluid are available in emergencies, but are not desirable, because they tend to dry out the cylinders, and are dangerous if used improperly. There are also liquid forms of starter fluid available which can be added to the gasoline.

Tetraethyl lead was used in some gasolines to reduce or prevent knocking. However, in 1975, it became illegal to use leaded gasoline except in cars built prior to this time. Methyl Tertiary Butyl Ether (MTBE) is used in unleaded fuel to increase the octane. Gasoline exposed to heat and air oxidizes and leaves a gummy film. Detergents are now added to gasoline to prevent this. The detergents keep the carburetor passages and fuel injectors free from deposits, which could cause hard starting and problems in driving. Deposits also restrict the flow of fuel and cause a rough idle, hesitation of acceleration, surging, stalling, and lack of power.

Alcohol is frequently used as an additive to commercial gasoline, because it will absorb any condensed moisture which may collect in the fuel system. Water will not pass through the filters in the fuel line, so, when any water collects, it will prevent the free passage of fuel. It also tends to attack and corrode the zinc die castings of which many carburetors and fuel pumps are made. This corrosion will not only destroy parts, but also clog the system and prevent the flow of fuel. By using alcohol in gasoline, any water present will be absorbed and pass through the fuel filter and carburetor jets into the combustion chamber. Alcohol additives are often purchased and added separately into the gas tank to prevent gas-line freeze and vapor lock.

The increasing cost of gasoline, and the new laws requiring alternative fuels have turned the attention of car and truck designers to substitutes. Chief among alternative fuels is alcohol. Considerable research has been done, and is still carried out, for alcohol in spark ignition engines. Alcohol fuels were used extensively in Germany during WWII, and alcohol blends are used in many vehicles at the present time.

Methanol and ethanol are the forms of alcohol receiving the most attention. Both are made from non-petroleum products. Methanol can be produced from coal, and ethanol can be made from farm products such as sugar cane, corn, and potatoes. Both alcohols have a higher octane number than gasoline. High heat of vaporization, however, indicates that the use of alcohol could give harder starting problems than gasoline, which means a need for a larger fuel tank and larger jet sizes in the carburetor. It requires less air for combustion, though, which compensates for the high calorific values. In proportion, this could result in practically the same air-fuel ratio for all three.

Experimental tests have shown that alcohol-fueled spark ignition engines can produce as much or slightly higher power than gasoline. Alcohol fuels have a higher self-ignition temperature than gasoline, which rates them better from a safety standpoint, but this same quality bars them from use in a diesel engine which depends on the heat of compression to ignite the fuel. At the present time, only ethanol can be blended in small concentrations (10%) with gasoline. Because of the high octane rating, alcohols can be used in relatively high compression ratios, and experiments indicate that emissions from engines fueled by alcohol would require the use of exhaust gas recirculation controls.

Diesel fuels vary from highly volatile jet fuels and kerosene, to the heavier furnace oil. Automotive diesel engines are capable of burning a wide range of fuel between these two extremes. How well a diesel engine performs with different types of fuel is dependent upon engine operating conditions and the fuel characteristics. The classification of commercially available fuel oils has been set up by the American Society for Testing Materials. Grade 1D fuels range from kerosene to what is known as intermediate distillates. Grades 2D and 4D each have progressively higher boiling points and contain more impurities. The fuels known as high-grade fuels, kerosene, and 1D fuels, contribute a minimum of engine deposits and corrosion and have less impurities. Refining the fuels removes the impurities, but it also lowers the heat value. Therefore, the higher grade fuels develop slightly less power than the same quantity of low-grade fuels. This is more than offset by the cost of maintenance repairs in using low-grade fuel.

A mixture of gaseous petroleum compounds, principally butane and propane, together with smaller quantities of similar gases, is known as liquified petroleum gas (LPG). LPG is used as fuel for internal combustion engines, mostly in the truck and farm tractor fields. It is chemically similar to gasoline, since it consists of a mixture of compounds of hydrogen and carbon, but it is a great deal more volatile. It is a vapor and when used as a fuel, a special kind of carburetor is required. When LPG is stored or transported, it is compressed and cooled so that it is a liquid. It is under tremendous pressure and needs extremely strong tanks. LPG is made of surplus material in the oil fields. It is becoming more widely used as an increasing number of trucks and tractors are being fitted with the equipment required to make use of it. Besides being low in cost, LPG has the advantage of having a high octane value (93 for pure butane; 100 for propane). Since it is a dry gas, LPG does not create carbon in an engine, and does not cause dilution of the engine oil. As a result, maintenance and internal parts replacement is highly reduced. Oil changes are also less frequent because it is a cleaner burning fuel than gasoline. Other advantages are easy cold weather starting, lack of exhaust odor, and elimination of evaporation.

A diaphragm is a flexible partition or wall separating two cavities. The lever can only be moved upward by the diaphragm spring. This process causes fuel to be delivered to the carburetor only when the fuel pressure in the outlet is less than the pressure maintained by the diaphragm spring.

The intake (or inlet) valve permits a fluid or gas to enter a chamber and seals against its exit. The outlet valve works just the opposite; permitting the pressurized fuel to flow out into the fuel lines to the carburetor.

A check valve above the fuel pump in the fuel line keeps the fuel from flowing back into the fuel tank when the engine is shut down. If this valve were not there, fuel starvation on start-up might occur, since it takes longer for the electric fuel pump to get up pressure in the fuel line than it does for a positive displacement mechanical pump.

The operating lever is hinged to the pump arm, so that it can move down but cannot be raised by the pump arm. The pump arm spring forces the arm to follow the cam without moving the lever. The lever can only be moved upward by the diaphragm spring.

Paper-element air filters were first introduced in 1957. The air cleaner element is the disposable dry type, which is made up of a cylindrical cellulose fiber material, pleated to permit the greatest filter area. On each end of this cylinder, the fiber is embedded in end plates to provide an efficient dust seal. On each side of the fiber, rust resistant wire screen furnishes compressive strength. The fine mesh located on the inner screen also acts as a flame arrester in case of backfire. The fiber passes air through the filter with low restriction, but any dust or dirt in the air is deposited on the pleated outer surface. The filter fiber is flame proof and keeps its filtering efficiency under normal concentrations of gasoline vapors, engine oil and water vapor, but should be changed at normal lubrication periods.

Air filters can be cleaned by blowing compressed air back through the filter, but the danger exists that small holes can be created by excessive pressure. For this reason, it is usually a good idea to simply replace the filter element.

Some air filters are of the washable variety, and can therefore be washed clean and re-used.

A good way to determine if your air filter is still OK is to look through the filter on a bright day. If you can't see the sun through the filter, it needs replacement.

The pintle valve is a spring-loaded ball inside the injector of a fuel-injection system. The injector coil creates a magnetic field, which causes the armature to move upward. This action pulls the pintle valve off its seat. Then, fuel under pressure can flow out of the injector nozzle. The contour of the ball or pintle valve causes the fuel to be sprayed in a cone-shaped pattern. When the injector is de-energized, the spring pushes the ball onto its seat, stopping the flow of fuel.

The height of the fuel in a tank causes the sending unit to send variations in resistance, which changes the current to the dash unit coil so the pointer indicates the amount of fuel available.

A calibrated friction brake is included in the fuel tank unit. This prevents the wave motions of the fuel from fluctuating the pointer on the dash unit, so that the fuel reading will correctly correspond to the amount of fuel available in the tank.

Current from the battery passes through the limiting coil to the common connection of two coils at the lower terminal on the dash unit. The current is then offered a choice of two paths, one through the operating coil of the dash unit and the other over to the tank sending unit.

When the fuel tank is low or empty, the sliding brush cuts out all resistance in the tank unit. Most of the current will then pass through the tank unit circuit because of the low resistance, and only a small portion will pass through the operating coil to the dash unit. As a result, this coil is not magnetized enough to move the dash unit pointer, which is then held at the "Empty" position by the limiting coil.

When the tank is partly full or full, the float of the tank unit will rise to the surface of the fuel and move the sliding brush over the rheostat, putting resistance in the tank unit circuit. More current will then pass through the operating coil to give a magnetic pull on the pointer, which overcomes some of the pull of the limiting coil. When the tank is full, the tank unit circuit contains the maximum resistance to the flow of the current. The operating coil will then receive its maximum current and exert pull of the pointer to give a "Full" reading.

As the tank empties, the operating coil loses some of its magnetic pull and the limiting coil will still have about the same pull so that the pointer is pulled toward the lower reading.

Vapor lock is a condition in which fuel boils in the fuel system, forming bubbles which retard or stop flow of fuel to the carburetor.

Gaskets compensate for small irregularities between two surfaces. They are used to prevent fluids and gasses from leaking. In the case of a cylinder head gasket, the combustion pressure is kept in the cylinder, and engine coolant is kept within the passages of the water jacket. The most common cause of gasket failure is overtightening of the bolts that hold the gasket between the metal surfaces. To prevent this, some manufacturers have incorporated a metal washer in the bolt holes of the gasket, which limits the amount of force that can be applied. Some gaskets must be installed in a specific manner, while others do not. Head gaskets require the mechanic to "torque" the head bolts to specific tightness, and also require the bolts to be tightened in a specific order.

A valve is a device for controlling flow through an opening. The internal combustion engine, which is basically an air pump, depends on the efficient sealing of the valves in order to produce compression. The timing of when the valves open, and the duration of their opening, affects engine operation. The cam dictates these two factors. The following terms describe the major components associated with the valves.

"Valve clearance" is the gap between the end of the valve stem and valve lifter or rocker arm to compensate for expansion due to heat. Engines with hydraulic lifters often do not need valve clearance adjustments because the lifters automatically take up the slack.

The "valve face" is the part of the valve which mates with and rests upon some seating surface. The "valve head" is the portion of a valve upon which the valve face is machined.

The "valve lock" (also called the key, keeper, or washer) is a device which holds the valve spring in place on the valve stem.

"Valve overlap" is an interval which is expressed in degrees where both valves (intake and exhaust) in each cylinder are open at the same time.

The "valve seat" is the part of the cylinder head upon which the valve face rests. These are precision ground to mate with the valve face and thereby seal the cylinder.

The "valve spring" is attached to the valve to return it to its seat after lift is released.

The "valve stem" is the longest portion of the valve which passes through the valve guide.

The "valve guide" is the sleeve through which the valve stem passes. It is pressed or threaded into the cylinder head, and is self lubricated by the composition of its materials. Older cars depend on the lead in "Regular" gas to lubricate the guides.

The "valve timing" refers to the relative position of a valve (either open or closed) to the piston in its travel, in crankshaft degrees.

The "valve train" is the complete set of mechanisms used to transmit the rotating motion of the engine crankshaft to the reciprocating valve stem, causing the valves to open.

The "heat exchanger" is a device that uses exhaust heat to aid in fuel evaporation. It usually is built into the intake manifold as an area where the hot exhaust gasses and fuel-air mixture come close to each other.

"Barrel" is a popular term for a carburetor throat. There is one venturi in each throat. A dual (or "two-barrel") carburetor has a primary venturi for part-load running and a secondary venturi for full-throttle; a four-barrel carburetor has two primary and two secondary venturis.

Methanol and ethanol are two forms of alcohol fuel receiving the most attention. Both are made from non-petroleum products. Methanol can be produced from coal, and ethanol can be made from farm products such as sugar cane, corn, and potatoes. Both alcohols have a higher octane number than gasoline. High heat of vaporization, however, indicates that the use of alcohol could give harder starting problems than gasoline, which means a need for a larger fuel tank and larger jet sizes in the carburetor. However, it requires less air for combustion, which compensates for the high caloric values.

Ethanol is the most common fuel additive; it's an alcohol made from vegetable matter. Some areas require the addition of oxygenates in gasoline, because they reduce carbon monoxide emissions by as much as 39%. They also raise the octane level of the gasoline.

"Baffle plates" are sometimes welded to the sides and bottom of the inside of the fuel tank for reinforcement and to prevent the fuel from surging and splashing. Baffle plates are notched or perforated so that the fuel can still flow from one section to another.

The throttle cable, or linkage, controls the throttle valve by connecting it to the accelerator pedal. Pressing on the pedal causes the linkage to open the throttle plate and the choke plate. This causes air to rush through the barrel.

The fuel vapor canister is used by the vapor recovery system to trap fuel from the carburetor float bowl and fuel tank. Starting the engine causes the vacuum port in the canister to pull fresh air into the canister to clean out the trapped fuel vapor. The trapped fuel vapor is then fed into the carburetor to be burned.

The gas, or accelerator, pedal is connected to the throttle valve by the throttle cable, or linkage. Pressing on the pedal causes the linkage to open the throttle valve, and thereby increase engine speed. A return spring on the throttle valve returns the pedal to its normal position when foot pressure pedal is released.

Vacuum lines are a series of hoses, or tubing, to the intake manifold. These hoses supply vacuum to various components of the engine, such as the emissions control system.

Most air conditioning systems have vacuum motors to open and close the doors on the air conditioning ducts. A vacuum motor is just a small diaphragm with connecting rods to activate the valves of the system. They have the advantages of simplicity and quietness.

A return spring, or restoring spring, is a coil spring that moves something, such as a valve or diaphragm back to its normal position and holds it there.

The diaphragm return spring is a stiff coil spring that pushes the diaphragm upward, flexing it in an upward direction.

The impeller is a wheel like device with a series of curved fins or vanes. As the impeller whirls, the air is drawn in at the center and thrown off at the rim; the air is then forced into the passage at increased pressure. The impeller shaft connects the impeller with the turbine.

The fuel tank filler neck is a long tube that goes down to the center of the gas tank. It is also equipped with vapor return lines. Some filling stations collect the fuel vapor as you fill your car.

The fuel rail is a fuel line that connects all of the injectors in a multipoint fuel injected system. It is usually 3/4" in diameter and allows a constant fuel supply to each of the injectors, which act independently. The fuel rail is filled with pressurized fuel from the fuel pump.

Diesel fuel pumps are designed to inject a specific amount of fuel at a very specific time. They control the injectors by the pressure waves of the fuel that they pump. They are usually linked to the crankshaft or the camshaft through a series of gears. These gears allow the fuel pump to be driven directly by the crankshaft of the engine. However, some are belt driven and some are chain driven. The diesel fuel pump has mechanisms in it which allows more or less fuel to be pumped. If less fuel is pumped into the cylinders, this slows the engine. Pumping more fuel increases the speed of the engine. Consequently, the fuel pump regulates the speed of the diesel engine.

The diesel fuel injector is a pressure valve, but it has specific components that allow it to disperse the diesel fuel in set patterns, depending on the design of the valve. Diesel fuel injectors receive the pressurized impulse from the diesel fuel pump, and allow the fuel to enter the combustion chamber when it is needed. If the diesel fuel injectors get clogged, engine performance suffers.

Glow plugs are used to warm the fuel mixture within the precombustion chamber in a diesel engine. A glow plug is an electric resistance wire within a small housing that is raised to a certain temperature when the engine is started (or "cold"). The fuel plug gets the fuel mixture up to the proper ignition temperature. Once the engine is warmed up, the glow plug control senses the temperature difference and turns off the glow plugs until they are needed again.

The precombustion chamber of a diesel engine is a small cavity, much like the combustion chamber, only it is contained within a small area. It allows a preignition state to exist. Once the fuel in the precombustion chamber ignites, it can then ignite the fuel- air mixture in the combustion chamber itself. In cold weather, the precombustion chamber enables diesel engines to start more readily, since the glow plug can easily warm the small volume within it. Under normal operating conditions, the precombustion chamber allows a lean mixture to be used, because it concentrates and ignites it within the precombustion chamber before it disperses into the combustion chamber.

The substance your car burns the most of is air. Fuel is mixed with the air at ratios of around 14.6:1. For every gallon of gas you burn, you burn many, many cubic feet of air. The number of molecules of air entering the combustion chamber each time the intake valve opens will vary with the temperature of the air. Cold air is much more dense (the molecules are packed together) than warm air, so cars often perform better in cool weather. If more air gets into the chamber, more power is produced. For this reason, engines running at high altitudes or in especially hot climates have to be specially tuned to get enough air to run properly. If the air is compressed by a turbocharger or supercharger, more of it can be packed into the cylinders. The result is the production of greater power when this air is ignited.

Although all of us know how to use the fuel filler cap, it is actually more complicated than it looks. Inside the fuel filler cap is a pressure release valve. This allows it to vent the fumes in the gas tank if they build up to predetermined levels. Until the fumes reach these levels, they are shunted through the charcoal canister which collects the fuel from the air before the air escapes. When the fumes build up above the predetermined (differing from car to car) threshold level of the fuel filler cap's pressure release valve, they are vented into the atmosphere. The fuel filler cap has a rubber flange around the neck. This flange should be inspected for cracks or inflexibility. If the flange does become cracked or inflexible, it should be replaced to keep the environment clean.

Operation is much like driving a car with an automatic transmission; there is an accelerator that controls forward movement, and a brake that when applied, slows the vehicle and at the same time recharges the batteries. A button is pressed for reverse. The GM Impact uses alternating current (AC) motors and a converter for utlizing the battery's power, which is DC. The car's main power source is a special battery pack. The main obstacle of battery power is its power to weight ratio. Lead batteries weighing the same as a full tank of gasoline have much less usable energy for the car to draw from. Also, as batterys lose their power, the performance drops gradually, which could be dangerous in traffic. There are many different battery types being developed, but the majority of designs use either nickel cadmium or lead-acid. Each has its advantages and disadvantages. Depending on their design and cost, the batteries can take anywhere from 20 minutes to ten hours to recharge. They provide ranges from 30 to 100 miles on a single charge.

Another important part of the electric car is the electronic control system. The energy management control, which encompasses both acceleration and deceleration, controls and monitors the power flow, and alerts the driver of a drop in power.

Volvo has explored building "hybrid" electric cars. The turbine hybrid gives you the best of both worlds; the option of running pure electric for urban driving, or turning on the gas-powered turbine engine in hybrid mode for cruising. The hybrid mode helps to overcome the limited range and performance of a pure electric car. Volvo has a test car that can top 100 mph in hybrid mode, runs up to 415 miles without refueling, and gets 45 mpg at a constant 55 mph.

A large number of American firms are developing electric cars. General Motors has taken the lead with an electric car that is slated for mass production in the mid 1990's, the Impact.

The Impact can go from 0-60 in 8 seconds, has a range of about 80 miles per charge, and only requires about 3 hours to recharge on any 220v circuit. Little routine maintenance is required, and the cost will be competitive with conventional gas-powered cars.

Some electric cars are equipped with solar cells located on the roof of the car, similar to a sunroof. These cells are used to collect sunlight and convert it into energy. The solar cell is used to augment the existing recharging system.

Camille Jenatzy, of France, drove a Jeantaud electric a record of sixty miles an hour on April 29, 1899. The high speed, however, burned out both the specially fabricated batteries and French interest in electric cars.

The electric car, scheduled for mass production in the mid 1990's, offers many advantages over traditional gas powered autos of today. The most obvious advantage is exhaust free operation. As smog levels continue to increase at an alarming rate, the need to lower emission levels becomes more and more important. With the advent of electric cars, a dramatic reduction in the nitrogen oxides (NOx), and nonmethane organic gases such as carbon monoxide and hyrocarbons is possible. These gases are major contributors to the deterioration of the ozone layer. Also, the reduction of particulates (tiny particles of dust, soot, smoke, and other matter floating in the air) would be cut to almost zero.

The Fuel System (Overview)