Development Of Carburetor


Development of carburetor

1876 : Carburetor invented by an Italian Luigi De Cristoforis.
1882 : Carburetor was develop at University of Padua by Enrico Bernardi, the first petrol combustion engine which is one cylinder engine prototyped on 5th August.
1885 : A float carburetor was developed by Wilhelm Maybach and Gottlieb Daimler for their base engine uses on the atomizer nozzle.
1893 : Hungarian engineer Jonas Csonka and Donat Banki invented the world's first carburetor that are use on stationary engine.
1896 : Frederick William Lanchester of Birmingham was experimented the wick carburetor on cars and called first gasoline-driven car in England.
1980 : The most Us-made gasoline fueler was using carburetor as the usual method of fuel delivery and the method is called 'fuel injection'.
1990 : Almost Australian's cars carburetor.
1993 : Honda Civic use carburetor.
1994 : Ford Laser.
1996 : Mazda 323 and Mitsubishi magna Sedans.
1997 : Daihatsu Charade.
1999 : Suzuki Swift.
2000 : A low cost commercial 4WDS and vans still used carburetor.
2003 : Mitsubishi Express Van.
2006 : Lada cars used carburetor.
2011 : The last car NASCAR's Sprint Cup Season the last one used carburetor.
2012 : All races car used the electronic fuel injection.
Principle of carburetor

The principles that is used by the carburetor is Bernoulli's Principle. As the principle states that as faster air moves, the lower its static pressure, and the higher its dynamic pressure. The accelerator linkage does not directly control the flow of liquid fuel but it actuates carburetor mechanism which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, will decide the amount of fuel that will drawn into the airstream. When carburetor is used in the aircraft with the piston engine, special design and features are needed to prevent fuel starvation during the condition of inverted flight. Then, the later engines used an early form of fuel injection known as pressure carburetor. The main disadvantage of basing a carburetor's operation on Bernoulli's Principle is that, being a fluid dynamic device, the pressure reduction in a venturi tends to be proportional to the square of the intake air speed. The fuel jets are much smaller and limited mainly by viscosity, so that the fuel flow tends to be proportional to the pressure difference. So jets sized for full power tend to starve the engine at lower speed and part throttle. Most commonly this has been corrected by using multiple jets.

Nowadays, there are few number of metering device that is used on the modern aircraft. Each of the metering device is varied in term of design to accommodate the different type of engine and aircraft designed purpose as well. nowadays, basically there are two types of metering device that are carburetor and fuel injection system. The main function of these metering device is to meter fuel to the engine. The two types of the fuel injection system are continuous and direct fuel injection system. As for the carburetor ;there are two types as well that are float type carburetor and pressure injection carburetor. Fuel system delivers a proper mixture of air and fuel to be burned efficiently. It must be store enough fuel so the car can complete a trip of a few hundred miles. Carburetor mixes the fuel and air in the right ratio to maximize the combustion inside the combustion chamber of the engine, and allows the vehicle operator to increase or decrease the available fuel/air mixture thereby controlling the engine power. It mixes fuel and air in the right ratio to maximize combustion inside the combustion chamber of the engine, and allows the vehicle operator to increase or decrease the available fuel/air mixture thereby controlling the engine power. Carburetor is also very important because if the carburetor is not working properly it will cause damage to the car's engine. This will result in the engine stalling and flooding.

CARBURETOR FUNCTION ON RECIPROCATING ENGINE AND HOW IT WORKS

OPERATING PRINCIPLE :
Based on Bernoulli's principle, the carburetor mixes fuel and air in the correct ratio. This range is in between 1:9 (rich, 1 part fuel to 9 part air) and 1:18 (lean). The chemically correct (stoichiometric) ratio for gasoline is 1:14, 7 by weight and provides the exact balance of oxygen and fuel for the most complete combustion and highest exhaust temperatures.
PISTON ENGINE OPERATION :
First, we need to know how the piston engine works, the cycle begins with the piston at the top dead center as the crankshaft pulls the piston downward, a partial vacuum is created in the cylinder chamber. And the cam arrangement has opened the intake valve and the vacuum causes a mixture of fuel and air to be drawn into the cylinder. Compression and ignition stroke as the crankshaft drives the piston upward in the cylinder, the fuel and air mixture is compressed. The intake valve has closed and as the upward stroke process begins. Then as the compression stroke is completed and just before the piston reaches its top position in the cylinder, the compressed mixture is ignited by the spark plug. Then power stroke part, the very hot gases expand with a very tremendous force and it drive the piston down the turning crankshaft. The valves are closed during this stroke. Exhaust stroke on the second upward stroke, the exhaust valve is opened and the burned gases are forced out by the piston. Then at the moment of the piston complestes the exhaust stroke, the cycle will start all over again by the intake stroke. Each of the piston within the engine must make four strokes to complete one cycle, and this complete cycle happened hundreds of times per minute as the engine keep on running.
1. Inward (down)intake
2. Outward (up) Compression and ignition
3. Inward (down) Power
4. Outward (exhaust)
Before gasoline can burn in a piston engine it needs to be vaporized and mixed with oxygen in the right quantities. This process is done by carburetor. For this process to be almost perfect the system needs to take into account, power setting, mixture control and such. The evaporation of fuel inside of the carburetor caused a drop in temperature possibly forming ice is humidity and outside air temperature conditions are right. Heat must be added to prevent this. Piston powered aircraft engines can use carburetor

CARBURETOR OPERATION
Carburetor has an open pipe for which the air passes into the inlet manifold of the engine. The pipe that is used inside the carburetor is in the form of venture. A carburetor mixes air and fuel in an appropriate portion. Air and liquid fuel are the inputs to the carburetor at different points of the carburetor. The venture that is used it narrows in section and then widens again, this will cause the airflow to increase in speed at the narrowest part of the venturi. . Due to suction that are created by the working engine, the atmosphere air is accelerated through the venture in the carburetor, accelerating of air sucks the fuel in the venture at its center from a level regulated liquid fuel pot in the carburetor, due to the venture action. (Bernoulli's Principle) during the process of sucking the fuel is atomized and becomes a mist, as it enter the venture. Then next after the venture section, there is a butterfly valve or known as throttle valve. It is a rotating disc that can be turned on to the airflow so that it can block the airflow completely and rotated to hardly restrict the flow at all. The butterfly valve control the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, therefore regulating engine power and speed.The throttle is connected through the cable and joints by the pneumatic link. The fuel is introduced to the airstream through small holes at the narrowest part of venture and other place that pressure will be lowered when not running on full throttle. Fuel flow is adjusted precisely calibrated orifices in the fuel path. The fuel that has been atomized will be evaporated and then mixes uniformly with the air. The mixture of fuel and air that has been uniformly mix will be the output of the carburetor. Then the gaseous mixture then will go to the engine cylinder for the combustion process.

BASIC CARBURETOR DIAGRAM

CABURETOR SYSTEM

5 CARBURETOR BASIC SYSTEM
Float System

The puprpose of float circuit is to maintain an adequate supply of liquid fuel at the proper, predetermined level in the bowl for use by the idle, accelaration pump, power and main metering circuits. One or 2 separate float circuits may be used, each circuit containing a float assembly, needle and a seat. All circuit ar esupplied with fuel from the bowl.
All fuel enters the fuel bowl through the fuel inlet fitting in the carburetor body. The fuel inlet needle seats in the fuel inlet fitting. The fuel inlet needle is controlled by a float and a level which is hinged by a float shaft.
The fuel inlet system must constantly maintain teh specified level of fuel as the absic fuel metering systems are calibrated to deliver the proper mixture only when the fuel is at this level. When the fuel level in bowl drops, the float also drops permitting additional fuel flow past the fuel inlet needle into the bowl.

Idle System

Fuel using during curb idle and low-speed operation flows through the main metering jet into the main well. A containning idle well intersects teh main well. An idle tube is installed in the idle well. Fuel travels up the well and mixes with air which enter through the idle air bleed located in the bowl cover. At curb idle the fuel and air mixture flows down the idle channel and is futher mixed or broken up by air entering teh idle channel through the transfer slot above the throttle plate. The id;e system is equipped with a restrictor in the idle channel, located between the transfers slot and the idle port, which limit the the maximum attainablr idle mixture. During low speed operation the throttle plate moves exposing the transfer slot and fuel begins to flow through teh transfer slotas well the idle port. As the throttle plates are opened futher and engine speed increases, the air flow through the carburetoral so increase. This increased air flow creates a vacuum in the venturi and the main metering system begins to discharge fuel.

Main metering System
As the throttle valve continue opening, the air flow through the carburetor increase and creatred a low pressure area in the venturi. This low pressure causes fuel to flow from teh fuel bowl through the main jets and into the main wells. Air from the main air bleed mixes the fuel through holes in the sides of main well tube. The mixtures is tehn drawn from th emain well tube and discharged through teh venturi nozzle. As air flow through the carburetor increases, teh amount of air fuel mixture discharged also increases.
On feedback carburetor, a mixture control solenoid or vacuum modualtor is used to ocntrol the air/fuel mixture. This can be done by regulating the amount of air bleed or fuel (in some case both are controlled) avaiable to teh main circuit. The solenoid or modulator actuates a stepped or taperred needle in theair bleed or main jets to do this. By controlling the amount of fuel released or air bleed, the solenoid/modualtor regualtes the total air/fuel mixture.

Accelarating Pump System
When the throttle paltes are opened suddenly, teh air flow thriugh the carburetor respond almost immediately. However, there is a breif time interval or lag the additional fuel can move the system and main tain the desired air/fual ratio. The accelerating pump provides a measured amount of fuel necessary to insure smooth engine operation upon accelaration.
When the throttle is opened, the pump plunger actuates the pump piston or diaphragm. This closes the intake check valve, forcing fuel out through the discharged passage and out through th pump jets. At higher speeds, pump discharged is no longer necessary to insure smooth acceleration. The external pump linkage is so constructed that less pump stroke is available whrn the throttle is in the higher speeds posititons.
As the trttle is closed, the pump piston or diaphragn return to its rest position and fuel is drawn into the pump as the check valve opens.

Power Enrichment System

During high speed (or lowmanifold vacuum) teh carburator must provide a richer tahn is needed when the engine is running at cruising speed. Added fuel for power operation is supplied by a power enrichment system. There are both vacuum and mechanically controlled systems.
On vacuum controlled systems, a passage in the throttle body transmits manifold vacuum to the piston camber in th ebowl cover. Under light throttle and light load condition, there is sufficient vacuum acting on the vacuum piston to overcome the piston spring tension. When the throttle valves are opened more, vacuum that is acting on the psiton is bled to atmosphere and minifold vacuum is closed of, insuring proper mixture for sufficiently, the holle in the trottle shaft will line up with the port in the base of carburetor, venting the piston vacuum chamber to atmosphere and allowing the spring loaded piston to open the power valve. As engine power demand reduced, and the throttle valve begin to close, valve and shuts off the added supply of fuel which is no longer required.
On mechanical systems, metering rod are directly actuated by the throttle linkage. As the throttle is opened towards the wide-open position, the metering rods are lifted from their jets. This allow additional fuel to pass.

FLOAT TYPE CARBURETOR :

This type of carburetor uses a chamber with a float. The chamber is filled with fuel and the float regulates the amount of fuel in the chamber. The fuel enters the venturi through a metered jet in the chamber. In the venturi air pressure has dropped by Bernoulli's principle. The fuel then vaporises and the resulting mixture is fed to the cylinders.
There is a throttle downstream of the venturi in the carburetor and connected to the throttle lever in the cockpit. For this simple carburetor to work satisfactory we need some extra systems.

IN TERM OF MAIN METERING : The main purpose of main metering system is to supply the correct amount of fuel to the engine at all speed above idle. The main metering system is comprised of one or more venture tube , a main metering jet and discharge nozzle, and a throttle fuel metering begins with the venture. As air flows throught the venture the pressure drop. It is this drop that the metering system relies on to meter the appropriate amount of fuel.
IN TERM OF IDLING : When the throttle is nearly closed the air flow in the venturi decreases so much that the fuel flow through the main jet becomes unreliable. There remains an air gap where the throttle valve almost touches the wall of the carb throat, this is where an outlet for fuel is created. The idling jet is also equipped with an air bleed for good fuel vaporisation.
IN TERM OF MIXTURE CONTROL : Manual mixture control is needed because at higher altitudes the volume of air is the same but its density is less. Therefore the amount of fuel must be reduced to prevent the mixture to become too rich. This usually done by back suction from the throat of the venturi or a needle which reduces the fuel flow to the main jet.
To relieve the pilot from this task, some carburetors (Rotax Bing) use an automatic system with an aneroid capsule reducing fuel flow by back suction or with a needle valve on the main jet.
IN TERM OF ACCELERATION : During rapid movement of the throttle air flow accelerates in the carburetor throat but as the fuel has more mass than air it is slower to move. The resulting mixture is too lean for the engine. To compensate this an accelerator plunger pump is added to the carburetor and this pump introduces extra fuel in parallel with the normal main jet.
IN TERM OF POWER ENRICHMENT : Power enrichment is used at high manifold and RPM settings to avoid detonation and overheating. This is done by increasing the fuel flow when the throttle is almost at its wide open range.

PRESSURE INJECTION CARBURETOR :

This carburetor differ from the float type. Pressure injection carburetor it does not utilize a float chamber to store fuel but it the fuel is delivered under pressure by fuel pump pressure through the carburetor and out the discharge nozzle. Since fuel pressure id responsible for forcing the fuel out of the discharge nozzle, there is no need to place the discharge nozzle directly in a venture. This will greatly reduce carburetor icing incidents and aids in fuel vaporization. Individual system for the fuel metering, mixture control, idling, and power enrichment are still required.

IN TERM OF MAIN METERING : It is to supply correct amount of fuel to the engine.as filtered air enter the carburetor body, some of its flow into an impact pressure annulus around the venturi. As impact air enter the annulus, its velocity decrease while the pressure increase. Then air is directed to the chamber of regulator unit where it press against one side of inner diaphragm. as air metering force builds, it overcomes spring tension and open poppet valve. This fuel meteringforce balance the air metering force to hold the poppet valve off its seat and proper amount of air enter the engine.

IN TERM OF MIXTURE CONTROL : Mixture control system it control and regulate the ratio of fuel and air that is supplied into the engine. This will allow the engine operator to control the fuel/air mixture so the engine can operate efficiently at various altitude and in variety of condition.

IN TERM OF ACCELERATION : An acceleration system provide an immediate but brief increase in fuel flow in the throat of the carburetor to enrich the mixture. The engine can accelerate smoothly and faster until the carburetor can deliver fuel at a rate that is proportional to the airflow. This system consist of 3 chambers that are air chamber, primary chamber, and fuel chamber.

IN TERM OF POWER ENRICHMENT : The power enrichment system provides extra fuel for operations above cruise power settings. Then the extra fuel is used to aid in engine cooling and help prevent detonation. The power enrichment on pressure carburetor may be accomplish with either a double step idle valve or by incorporating an airflow power enrichment valve.

REFERENCES

[1] Packer, Ed (July 1953). "Know Your Carburetor - what it is, what it does". Popular Mechanics 100 (1): 181'184.
[2} Knuteson, Randy. "Old Faithful - Marvel(ous) Schebler carburetor" (PDF). Aircraft Maintenace Technology. Retrieved 19 January 2014.
[3] Lind, W. L. (1920). Internal-combustion engines; Their principles and applications to automobile, aircraft, and marine purposes. Boston: Ginn.
[4] Hillier, V.A.W.; Pittuck, F.W. (1966). "Section 3.6". Fundamentals of Motor Vehicle Technology (Second ed.). Hutchinson Educational
[5] http://www.youtube.com/watch?v=MiO-3vplZis
[6] American Technical Society. (1921). Automobile engineering; A general reference work. Chicago: American technical society.

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