Multiple carburetor barrels

While basic carburetors have only one Venturi, many carburetors have more than one Venturi, or "barrel". Two barrel and four barrel configurations are commonly used to accommodate the higher air flow rate with large engine displacement. Multi-barrel carburetors can have non-identical primary and secondary barrel(s) of different sizes and calibrated to deliver different air/fuel mixtures; they can be actuated by the linkage or by engine vacuum in "progressive" fashion, so that the secondary barrels do not begin to open until the primaries are almost completely open. This is a desirable characteristic which maximizes airflow through the primary barrel(s) at most engine speeds, thereby maximizing the pressure "signal" from the Venturis, but reduces the restriction in airflow at high speeds by adding cross-sectional area for greater airflow. These advantages may not be important in high-performance applications where part throttle operation is irrelevant, and the primaries and secondaries may all open at once, for simplicity and reliability; also, V-configuration engines, with two cylinder banks fed by a single carburetor, may be configured with two identical barrels, each supplying one cylinder bank. In the widely seen V8 and 4-barrel carburetor combination, there are often two primary and two secondary barrels.

The spread-bore four-barrel carburetor, first released by Rochester in the 1965 model year as the "Quadrajet" has a much greater spread between the sizes of the primary and secondary throttle bores. The primaries in such a carburetor are quite small relative to conventional four-barrel practice, while the secondaries are quite large. The small primaries aid low-speed fuel economy and driveability, while the large secondaries permit maximum performance when it is called for. To tailor airflow through the secondary Venturis, each of the secondary throats has an air valve at the top. This is configured much like a choke plate, and is lightly spring-loaded into the closed position. The air valve opens progressively in response to engine speed and throttle opening, gradually allowing more air to flow through the secondary side of the carburetor. Typically, the air valve is linked to metering rods which are raised as the air valve opens, thereby adjusting secondary fuel flow.

Multiple carburetors can be mounted on a single engine, often with progressive linkages; two four-barrel carburetors (often referred to as "dual-quads") were frequently seen on high performance American V8s, and multiple two barrel carburetors are often now seen on very high performance engines. Large numbers of small carburetors have also been used (see photo), though this configuration can limit the maximum air flow through the engine due to the lack of a common plenum; with individual intake tracts, not all cylinders are drawing air at once as the engine's crankshaft rotates.

Carburetor adjustment

The fuel and air mixture is too rich when it has an excess of fuel, and too lean when there is not enough. The mixture is adjusted by one or more needle valves on an automotive carburetor, or a pilot-operated lever on piston-engined aircraft (since the mixture changes with air density and therefore altitude). Independent of air density the (stoichiometric) air to gasoline ratio is 14.7:1, meaning that for each mass unit of gasoline, 14.7 mass units of air are required. There are different stoichiometric ratios for other types of fuel.

Ways to check carburetor mixture adjustment include: measuring the carbon monoxide, hydrocarbon, and oxygen content of the exhaust using a gas analyzer, or directly viewing the color of the flame in the combustion chamber through a special glass-bodied spark plug sold under the name "Colortune"; the flame color of stoichiometric burning is described as a "Bunsen blue", turning to yellow if the mixture is rich and whitish-blue if too lean. Another method, widely used in aviation, is to measure the exhaust gas temperature, which is close to maximum for an optimally adjusted mixture and drops off steeply when the mixture is either too rich or too lean.

The mixture can also be judged by removing and scrutinizing the spark plugs. black, dry, sooty plugs indicate a mixture too rich; white or light gray plugs indicate a lean mixture. A proper mixture is indicated by brownish-gray plugs.

On high-performance two-stroke engines, the fuel mixture can also be judged by observing piston wash. Piston wash is the color and amount of carbon buildup on the top (dome) of the piston. Lean engines will have a piston dome covered in black carbon, and rich engines will have a clean piston dome that appears new and free of carbon buildup. This is often the opposite of intuition. Commonly, an ideal mixture will be somewhere in-between the two, with clean dome areas near the transfer ports but some carbon in the center of the dome.

When tuning two-strokes It is important to operate the engine at the rpm and throttle input that it will most often be operated at. This will typically be wide-open or close to wide-open throttle. Lower RPM and idle can operate rich/lean and sway readings, due to the design of carburetors to operate well at high air-speed through the Venturi and sacrifice low air-speed performance.^[15]

Where multiple carburetors are used the mechanical linkage of their throttles must be properly synchronized for smooth engine running and consistent fuel/air mixtures to each cylinder.

Feedback carburetors

In the 1980s, many American-market vehicles used special feedback carburetors that could change the base mixture in response to signals from an exhaust gas oxygen sensor. These were mainly used because they were less expensive than fuel injection systems; they worked well enough to meet 1980s emissions requirements and were based on existing carburetor designs. Frequently, feedback carburetors were used in lower trim versions of a car (whereas higher trim versions were equipped with fuel injection). However, their high complexity (compared to both older carburetors and fuel injection) both made problems common and maintenance difficult. Eventually falling hardware prices and tighter emissions standards caused fuel injection to supplant carburetors in new-vehicle production.

Catalytic carburetors

A catalytic carburetor mixes fuel vapor with water and air in the presence of heated catalysts such as nickel or platinum. This is generally reported as a 1940s-era product that would allow kerosene to power a gasoline engine (requiring lighter hydrocarbons). However reports are inconsistent; commonly they are included in descriptions of "200 MPG carburetors" intended for gasoline use. There seems to be some confusion with some older types of fuel vapor carburetors (see vaporizors below). There is also very rarely any useful reference to real-world devices. Poorly referenced material on the topic should be viewed with suspicion.

Vaporizers

A cutaway view of the intake of the original Fordson tractor (including the intake manifold, vaporizer, carburetor, and fuel lines). Internal combustion engines can be configured to run on many kinds of fuel, including gasoline, kerosene, tractor vaporizing oil (TVO), vegetable oil, diesel fuel, biodiesel, ethanol fuel (alcohol), and others. Multifuel engines, such as petrol-paraffin engines, can benefit from an initial vaporization of the fuel when they are running less volatile fuels. For this purpose, a vaporizer (or vaporiser) is placed in the intake system. The vaporizer uses heat from the exhaust manifold to vaporize the fuel. For example, the original Fordson tractor and various subsequent Fordson models had vaporizers. When Henry Ford & Son Inc designed the original Fordson (1916), the vaporizer was used to provide for kerosene operation. When TVO became common in various countries (including the United Kingdom and Australia) in the 1940s and 1950s, the standard vaporizers on Fordson models were equally useful for TVO. Widespread adoption of diesel engines in tractors made the use of tractor vaporizing oil obsolete.

List of manufacturers

· AMAL, producer of carburetors and hand controls for British motorcycles and light industrial engines

· Argelite, producer of Holley and Magneti Marelli carburetors for the Argentinian market

· Autolite, a division of the Ford Motor Company from 1967 to 1973

· Ball & Ball, U.S. manufacturer, eventually part of Carter

· Bendix Stromberg and Bendix Technico carburetors used on aircraft and vehicles made by Chrysler, IHC, Ford, GM, AMC, and Studebaker

· Bing Carburetor, used on motorcycles, mopeds, aircraft, boats

· Carter, used on numerous makes of vehicles, including those made by Chrysler, IHC, Ford, GM, AMC, and Studebaker, as well as on industrial and agricultural equipment and small engines.

· Claudel-Hobson, UK

· Dell'Orto carburetors from Italy, used on cars and motorcycles

· Demon Carburetors

· Edelbrock performance carburetors

· Hitachi, found on Japanese vehicles

· Holley, with usage as broad as Carter and Weber

· Jikov, used on various "Eastern Bloc" cars and motorbikes, predominantly Škoda, Tatra, Wartburg, Jawa etc.

· Keihin, a keiretsu group company affiliated with Honda

· Lectron Fuel Systems carburetors

· Marvel Schebler, used for aircraft, tractors, ...

· Mikuni, common on Japanese motorcycles, especially in the 1980s. Mikuni also made racing carburetors for Japanese, British and European cars. Original equipment on Mitsubishi engines.

· Motec Engineering - high-performance updraft carburetors

· Pierburg, in Saab, Volvo, VW, and Audi

· Reece Fish, in Volkswagen, Austin Mini, Morris Mini

· Rochester Products Division, USA (A General Motors subsidiary; also sold Weber/Magneti Marelli carburetors under license)

· Solex - French carburetors, owned by Weber

· Stromberg - see Zenith

· SU carburettors, widely used on British Commonwealth and European-designed vehicles

· UCAL Fuel Systems - Carburettors

· Villiers UK motorcycle and small engines

· Walbro and Tillotson carburetors for small engines

· Weber carburetor, Italian, now made in Spain, owned by Magneti Marelli

· Zenith, UK. Used on Austin cars. Also produced the Zenith-Stromberg carburetors.

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive engines, having replaced carburetors during the 1980s and 1990s. A variety of injection systems have existed since the earliest usage of the internal combustion engine.

The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream.

Modern fuel injection systems are designed specifically for the type of fuel being used. Some systems are designed for multiple grades of fuel (using sensors to adapt the tuning for the fuel currently used). Most fuel injection systems are for gasoline or diesel applications.

Objectives

The functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system is optimized. There are several competing objectives such as:

· Power output

· Fuel efficiency

· Emissions performance

· Ability to accommodate alternative fuels

· Reliability

· Driveability and smooth operation

· Initial cost

· Maintenance cost

· Diagnostic capability

· Range of environmental operation

· Engine tuning

The modern digital electronic fuel injection system is more capable at optimizing these competing objectives consistently than earlier fuel delivery systems (such as carburetors). Carburetors have the potential to atomize fuel better (see Pogue and Allen Caggiano patents).

Benefits

Driver benefits

Operational benefits to the driver of a fuel-injected car include smoother and more dependable engine response during quick throttle transitions, easier and more dependable engine starting, better operation at extremely high or low ambient temperatures, smoother engine idle and running, increased maintenance intervals, and increased fuel efficiency. On a more basic level, fuel injection does away with the choke, which on carburetor-equipped vehicles must be operated when starting the engine from cold and then adjusted as the engine warms up.

Environmental benefits

Fuel injection generally increases engine fuel efficiency. With the improved cylinder-to-cylinder fuel distribution of multi-point fuel injection, less fuel is needed for the same power output (when cylinder-to-cylinder distribution varies significantly, some cylinders receive excess fuel as a side effect of ensuring that all cylinders receive sufficient fuel).

Exhaust emissions are cleaner because the more precise and accurate fuel metering reduces the concentration of toxic combustion byproducts leaving the engine, and because exhaust cleanup devices such as the catalytic converter can be optimized to operate more efficiently since the exhaust is of consistent and predictable composition.

History and development

Herbert Akroyd Stuart developed the first device with a design similar to modern fuel injection, using a 'jerk pump' to meter out fuel oil at high pressure to an injector. This system was used on the hot bulb engine and was adapted and improved by Bosch and Clessie Cummins for use on diesel engines (Rudolf Diesel's original system employed a cumbersome 'air-blast' system using highly compressed air Fuel injection was in widespread commercial use in diesel engines by the mid-1920s.

An early use of indirect gasoline injection dates back to 1902, when French aviation engineer Leon Levavasseur installed it on his pioneering Antoinette 8V aircraft powerplant, the first V8 engine of any type ever produced in any quantity.

Another early use of gasoline direct injection (i.e. injection of gasoline, also known as petrol) was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925.^[2][3] Hesselman engines use the ultra lean burn principle; fuel is injected toward the end of the compression stroke, then ignited with a spark plug. They are often started on gasoline and then switched to diesel or kerosene.

Direct fuel injection was used in notable World War II aero-engines such as the Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-82FN (M-82FN). German direct injection petrol engines used injection systems developed by Bosch from their diesel injection systems. Later versions of the Rolls-Royce Merlin and Wright R-3350 used single point fuel injection, at the time called "Pressure Carburettor". Due to the wartime relationship between Germany and Japan, Mitsubishi also had two radial aircraft engines utilizing fuel injection, the Mitsubishi Kinsei (kinsei means "venus") and the Mitsubishi Kasei (kasei means "mars").

Alfa Romeo tested one of the very first electronic injection systems (Caproni-Fuscaldo) in Alfa Romeo 6C2500 with "Ala spessa" body in 1940 Mille Miglia. The engine had six electrically operated injectors and were fed by a semi-high-pressure circulating fuel pump system.