Fuel Injection Technology - An integral Part of Engine Design
Modern legislation covering car emissions and the move towards a cleaner-greener environment has provided the incentive to develop and introduce advanced electronic technologies that can monitor fuel demand, oxygen requirements, air density, temperature then look-up an optimal performance graph and compute how to burn the fuel source efficiently with minimum emissions.
It then shunts just right amount of air into the combustion chamber, opens a valve, injects just the right amount of fuel (not too much, not too little). The fuel ignites at just the right moment to get the most force from the explosive air-fuel mixture. And this all happens within the blink of an eye before repeating the entire process for the next combustion chamber.
Meanwhile, the exhaust gases are checked to see that the whole process worked as predicted and deciding if any adjustments are needed.
Fuel injection becomes a vital and variable part of a complex electronic prediction, monitoring and adjustment loop that repeats millisecond by millisecond and relies upon every part of the system working correctly.
The inbuilt computational power of the electronic control unit ECU can do all this while taking care of the braking system, cooling system, cabin comfort and making sure the battery recharges properly.
The carburettor, being primarily a mechanical fuel delivery system could not cope with the infinite matrix of variables needed to keep emissions within legislated tolerances and still make the most efficient use of the fuel it delivers.
Multi Port Fuel Injection - Sequential Fuel Injection
Multi-port fuel injection have a dedicated fuel injector for each cylinder. Normally, the injector is situated to spray directly at the intake valve. Sequential systems benefit from accurate fuel metering and fast response.
Throttle Valve Behaviour
The car accelerator pedal is attached to a throttle valve by a mechanical link or via a modern electronic position sensor. The throttle valve regulates the amount of air entering the engine not the amount of fuel injected.
Acceleration and Oxygen Demand
As the accelerator pedal is pressed, the throttle valve opens to let more air into the engine. Sensors monitor the air-mass flow into the engine and the lambda sensor reports the level of oxygen leaving the engine in the exhaust gases.
The engine control unit (ECU) responsible for fuel delivery monitors the throttle valve position. Sensing the change, it increases the fuel delivery rate in response to amount of air entering the engine.
There is an immediate estimated response so that the air reaches the cylinder with enough fuel to burn.
The sensors feedback combustion information and the fuel delivery is fine tuned to adapt to the new air intake level. This continuous process ensures an ideal air-to-fuel ratio.
The Fuel Injector
A fuel injector is an electronically controlled valve transferring pressurised fuel through a pipe or fuel rail supplied by the fuel pump into the engine combustion chamber.
Fuel Injector Construction
In response to a signal from the ECU an injector solenoid opens the fuel delivery valve and pressurised fuel is forced through an atomising nozzle sending a fine mist of fuel into the combustion chamber.
The atomised fuel has a huge surface area making combustion rapid and complete.
Fuel Injection - Pulse Width - Controlling Fuel Delivery
As mentioned, The ECU sends a signal to control the Fuel Injector. By varying the length of time the valve stays open controls fuel. The ECU sends an electrical pulse and the pulse width controls how long the valve stays open.
Engine Mapping
The pulse width is determined by comparing data from the various engine sensors with data programmed or mapped into look-up tables pre-programmed into the ECU. Unlike previous mechanically controlled fuel delivery systems, modern engine performance is most effectively adjusted by re-mapping the ECU to change its pre-programmed response.
Engine re-mapping can adjust or replace the look-up tables supplied by the manufacturer to optimise for fuel-efficient driving on roads to maximum controlled acceleration under race conditions.
Engine mapping can help correct an engine that has changed in tolerance due normal to wear and tear.