Previously, vehicles just required a carburetor to mix the fuel and air in the right proportions (airfuel ratio) before it delivered it into the combustion chamber.
This mixture would then be ignited into an explosion that would move the pistons which in turn made the engine run. Fuel will not burn without the oxygen extracted from the air and the function of the carburetor is to control the quantity and proportion of petrol and air entering the engine cylinders.
This will in turn determine the power output and speed of the vehicle. The carburetor atomises the petrol into a fine spray of very small droplets that will readily vaporize into a consistent combustible mixture. This allows the engine to idle smoothly and have no flat spots when the throttle is opened.
Carburetor-based petrol fuel systems which have worked well for many years are being phased out.
This is due to the high demands for better fuel economy, lower exhaust emissions, increased power output and more flexible engine performance. This can only be met by more complex carburetors and ancillary systems. Most modern vehicles now have a fuel injection system, because this is cheaper and more efficient.
This is readily combined with an electronic engine management system for total fuel and consumption control to form an Electronic Fuel Injection (EFI) management.
The management of the fuel system is carried out by an Electronic Control Unit (ECU), which is a specialized microcomputer. This controls all aspects of the engine management and is also able to monitor the engine speed and load more accurately. It is also able to gather and use other information, such as engine temperatures and ignition timing conditions.
The ECU-controlled injectors electrically open the ‘taps’ for varying periods of time to allow pressurized fuel to be sprayed into the combustion chambers and to mix with the air for the smooth running of the engine. The degree of this action will vary with the capacity of the engine, load and the speed of each particular vehicle.
EFIs therefore actually came on to the scene as a result of the failures and inefficiencies of the carburetor. This led to the improved current system, although this is operated electrically, unlike the carburetor which worked mechanically, and depended on the pressure from the engine chamber to deliver the fuelair mixture.
The latest improvement to the fuel delivery system is the VVT-i, which we will look at another day. Robert Kato is a mechanic who can be reached on:
Source : The Observer