The operation of a motor It is something that we take for granted: in modern cars and motorcycles, we just need to turn a key to leave and travel serenely wherever we are. However, the life of the drivers has not always been so simple: before theelectronic injection and on -board computers, in fact, was the carburetora component of internal combustion engines, to “feed” our engines with the right amount of fuel, mixing fuel And air in the right proportion necessary for the operation of the engine itself. However a relatively simple object is, it has different limits related to less adaptabilitythe need for maintenance and greater polluting emissions. To date, the anti-pollution rules led to a progressive disappearance of the carburetor, in favor of more precise and less polluting systems, but continues to be used in countries where the ease of repair and the possibility of finding low cost spare parts they count more.
The delicate balance of a combustion engine
The carburettor is a component of the fundamental internal combustion engines for their correct functioning. An engine a internal combustion must receive, in the tank through the appropriate pump, one adequate fuel dose, Typically petrol, to be able to turn on and work regularly.
In this type of engines, thechemical energy of the fuel is converted into mechanical energy through a process of combustion which takes place in very few milliseconds. The fuel, in order to be able to burn so quickly, cannot enter the engine in liquid form, but it must be finely mixed in the air, forming almost one fog: This is one of the main functions of the carburettor.
The other fundamental function is to send the right amount of fuel and air: the Air/fuel ratio ideal is said Stechiometric relationship And for the common petrol it is of 14.7 g of air for 1 g of fuel. The engine can also work with different air/petrol proportions: in case of excess of air we talk about “lean” mixture, Of “fat” When it is the gas to be in excess, but in both cases one excessive imbalance can lead to shutdown or al engine damage.
How the adjustment of the air and fuel takes place
The carburetors are often extremely complex and different from each other, depending on the expected use and cost: certainly not a topic negotiable in a few lines. Simplifying, however, we can say that a “modern” carburetor mixes petrol and air thanks to physical principle called effect Venturi: forcing the passage of air through a narrowingi gases accelerate locally causing a lowering of the pressure. This “emptiness” allows you to suck a small amount of fuelusually contained in an underlying tray connected to the tank, which comes finely sprayed from the air flow that invests it.
The maximum quantity of aspirable air comes controlled by a valvecommanded by the pedal (or the knob, in motorcycles) accelerator: if it remains closed limits the aspiration of air and the engine remains at low lapsWhile accelerate And by opening it the engine is “free” of forfeiting more air and more fuel, gaining power quickly.
Depending on the temperature, from the atmospheric pressure and of thealtitude, there air density change And with it also changes the quantity of oxygen present in a given volume: this means that, depending on the season or from the location, It is necessary region The quantities of petrol and air that reaches the engine. To do this, carburetors are often equipped with various registers (usually, screw) for increase or decrease manually the petrol sent to equality of aspirated air.
The limits of the carburettor
Over the years the carburetors have become increasingly complex and efficient, but today they show theirs limitsboth in terms of pollution and adaptability, for example traveling to mountain areas where they face each other in a few hours important changes in altitude.
The more we find ourselves high, the more the air becomes rarefied and this progressive rarefaction of the air favors the formation of a “fat” mixture, richer than gas: this leads to a greater pollution, because it remains more Sbuing petrol in the exhaust gas. Furthermore, with the accumulation of petrol in the combustion chamber, the risk of “swelling” The engine, that is, suffocate it and make it turn off.
To pollute less, modern engines must function with quite “thin” mixtures: thanks to the excess of air this leads to Complete combustion of fuel, minors unloading emissions and a greater one efficiency (plus km per liter of petrol). A too thin mixturehowever, does excessively increase temperatures of the engine bringing to greater wear and damage.
To reduce emissions and adapt to anti-pollution regulationsit is therefore better to have lean mixtures and it has therefore become essential to constantly and precisely control the air/petrol ratio. This is possible thanks to‘injection electronicsa system capable of adapting the amount of fuel Based on the calculations of the on -board computer, what measures theresidual oxygen in exhaust gases with Sensors called Lambda probes (λ).
As an indirect consequence of anti-pollution regulations, carburetor vehicles are gradually disappearing, especially in markets where the legislator places limits to emissions. His fortune, in the countries in which he is still used lies in the lack of special rules, even if more and more countries are adapting, and in being less expensive e easier to repair Also with scarce means. Also for this many “Globetrotter” travelersthat often travel to unpaid areasstill prefer rely on more dated meansgiven the difficulties of being delivered modern spare parts in remote regions.
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