Multi-Point Fuel injection or Port injection

In multi-point fuel injection (MPFI) technology, every cylinder in the combustion chamber of the engine is given an injector at the front of their inlet valves (outside the intake port), which is why it’s also called ‘Port Injection’.

Every injector sprays fuel at the same time and each cylinder gets a more precise volume of fuel, with less possibility of fuel condensation outside the intake manifold. While MPFI has the advantage of lower fuel wastage as compared to TBI, since the fuel is sprayed at the same time in all the cylinders, it doesn’t get properly synced with the rotation of all the pistons. This results in the fuel idling in the engine and port for as long as 150 milliseconds. All the same, from the performance point of view, the MPFIs function much better as compared to TBIs.

The sequential fuel injection system eliminates the only disadvantage of MPFI and is the most widely used fuel injection system today. In a sequential fuel injection system, the fuel injectors function with respect to the cylinders they are connected to. Every injector injects the fuel only when the intake valve of the cylinder opens. It remains idle for the rest of the steps. An ECU monitors the movement of cylinders and triggers the injectors only when required. The sequential fuel injection is the most effective and efficient of all the fuel injections systems currently available in the automotive industry.

In direct fuel injection, the system is focused on placing the injector inside the cylinder to directly inject the fuel, bypassing the intake valve or manifold. While this type of fuel injection system is usually seen in diesel engines, it has a significant space in petrol engines as well, where it’s known as GDI (gasoline direct injection).

In the previously mentioned systems, the fuel is sprayed on the intake and there is always a potential of fuel condensation to some extent. However, in the DI system, all the fuel is directly injected into the cylinder which produces maximum fuel economy and this is its greatest advantage. In diesel engines, direct fuel injection has been used since the 1920s, whereas, in petrol engines, it’s been used since around World War II. Automakers have also found that GDI engines are relatively more powerful and quite convenient for better CNG fuel efficiency.