Carburettor to Injection System

Carburettor to Injection System Rating  :      
The good old carburetor, which was a device that mixed the petrol and air into an atomized fuel –air supply to the cylinders has given way to modern day Fuel Injection systems that are factory calibrated and function using chip based Engine Control Modules (ECMs) that decide when and how much of fuel is to be injected into the cylinders basis various parameters monitored by the ECM such as throttle position, load, temperature, speed, etc.
Carburettors varied from simple to complex devices. But were at the end of the day mechanical devices. The main function of the Carburettor is to mix air and fuel and supply it to the engine cylinders through the inlet manifolds in the ideal stoichiometric air-fuel ratio of 14.7 : 1 (14.7 parts of air for every one part of fuel).

The throttle linkage on the carburetor defines the aperture of the venture throough whch the air gets pulled into the carburetor. The speed and pressure of the air define how much of the fuel will get sucked and sprayed into the carburetor venturi.

There are various types of Carburettors (down-draft, side draft and up-draft) and carburetors themselves could be single or multiple venture type. While a single carburetor is good enough for small engines multiple carburetors could be installed for bigger capacity engines.
The mechanical nature of carburetors make them prone to over or under metering of air-fuel mixture which could result in higher exhaust emissions. With the advent of tighter emission standards manufacturers have moved over to more efficient though more expensive Electronic Fuel Injection (EFI) system instead of carburetors.

The injection system could be a single injector throttle body system or a multiple injector system where each cylinder has a dedicated injector that sprays fuel at high pressure (high pressure injection of fuel through minute apertures atomises the fuel) in the cylinder’s air flow at the appropriate time and in the right quantity as governed by the Engine Control Module (ECM).

The ECM determines how much of fuel to be injected an in a Sequential Fuel Injection (SFI) a cam position sensor determines when and in which cylinder the injector is to be fired. The ECM picks up inputs from the Mass Air Flow (MAF) sensor, Throttle Position Sensor (TPS) in the throttle body, Coolant Temperature Sensor (CTS) and Cam Position Sensor (CPS) and O2 Sensor (Oxygen Sensor in closed loop systems) to determine the mass of fuel to be injected in the cylinders.

The EFI does away with variances that come in way of efficient fuel supply as compared to mechanical carburetion systems and therefore is more efficient and enables manufacturers to obtain lower emissions from engines. An engine with EFI will be more powerful and less polluting than the same engine with a mechanical carburetion system.

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