By all odds, the engine is the most important part of any car, and its life very much depends upon the way fuel is supplied to it. While carburettors used to do this duty until the mid-90s, it was in the late 90s when multi point fuel injection systems made their way to the Indian market, and then rapidly popularised themselves for their best efficiency. The multi point fuel injection system is one of the best engineering marvels ever produced, and today, every petrol and CNG car, irrespective of its price, comes with MPFI. In this article, we learn what MPFIs are and how they function.
How Does the MPFI System work?
Before MPFI let’s learn a bit about carburettors. The carburettors mix the air-fuel in the required ratio, and supply it to the intake manifold. Due to the absence of electronic control, a carburettor cannot properly measure the air-fuel ratio with changing air pressure and fuel temperature
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’. These fuel injectors inject an optimum quantity of fuel into the combustion chamber, which also results in better atomization and swirl of fuel in the combustion chamber. As every cylinder has a specific injector, there is a negligible possibility of fuel condensation outside the intake manifold. The components of MPFI are
- Fuel pressure regulator
- Fuel injectors
- Cylinders
- Pressure spring
- Control diaphragm
In the system, multiple fuel injectors are situated upstream of the cylinders’ intake valves. The fuel pressure regulator is connected to the fuel rail and governs the fuel flow. Meanwhile, the control diaphragm and pressure spring control the inlet valve opening and the amount of fuel that can return. The engine speed and load vary the pressure in the intake manifold.
Types of Multi Point Fuel Injection System
Sequential MPFI system
In a sequential multi point fuel injection system every injector nozzle works independently and they are timed like spark plugs to spray the fuel immediately before or as their respective intake valves open. This results in negligible fuel idling outside the intake valves and the maximum fuel is burnt for power generation, improving efficiency, power and reducing emission.
Batched MPFI system
Batched MPFI systems are employed in race cars that function at high engine RPM speeds. At these high RPMs, standard sequential fuel injection systems won’t be able to adequately spray the fuel required by the engine to ensure combustion. To ensure the engine receives the fuel it needs, a batched MPFI system injects fuel when the intake valve is open as well as when it is closed. Thus, when the intake valve opens, the cylinder receives a ‘batch’ of fuel, so to speak. Based on its function, a batched MPFI system will use more fuel. However, since its use is primarily for performance engines, fuel efficiency is not a major concern.
Advantages of Multi Point Fuel Injection System
- Since there is negligible fuel idling outside the intake valves, maximum fuel is burnt resulting in maximum power output. For example, the old carburettor-equipped Maruti 800 (produced from 1983-2000) would deliver 35-40 PS of power and the MPFI-equipped Maruti 800 delivers 47 PS of power.
- MPFI-equipped engines vibrate less, resulting in a smoother driving experience as compared to that of carburettor-equipped cars.
- As every cylinder has its own fuel injector, the fuel injection in the cylinder is quicker as opposed to that in the single point fuel injection system. This makes MPFI-equipped engines more responsive.
- Maximum fuel is burnt in MPFI and there is negligible fuel deposition outside the intake valves as compared to single point fuel injection system and carburettors. Thus MPFIs deliver a better fuel efficiency and lesser emission.
Disadvantages of Multi Point Fuel Injection System
- It requires regular inspection of fuel injectors
- The system is expensive compared to carburettors.
- Complex design and can be tedious to repair as compared to carburettors
Summary of Multi Point Fuel Injection System
To summarise, the multi point fuel injection system is by far the best and most successful fuel injection system and hence is installed in every petrol car out there. The MPFI has far more advantages than limitations, and most importantly, it greatly extends the engine’s life. This article will edify you through and through about MPFIs and will help you maintain your car’s engine more adequately.
FAQs about Multi Point Fuel Injection System (MPFI)
Q. What is MPFI engine technology?
A Multi-point fuel injection system has a separate injector nozzle for each cylinder, right outside its intake port, which is why the system is also called port injection. These fuel injectors inject an optimum quantity of fuel into the combustion chamber, which also results in better atomization and swirl of fuel in the combustion chamber
Q. What is the difference between single and multi point fuel injection?
A single-point injection system features a common fuel injector for all the cylinders in the combustion chamber of the engine. This is the oldest and simplest form of fuel injection system. In place of the carburettor, the single-point injection uses one or two fuel injector nozzles in the throttle body which is why it’s called Throttle body injection (TBI) as well. 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’.
Q. Is MPFI used in petrol engines?
Yes, MPFI is used in petrol engines.
Q. Is MPFI used in diesel engines?
No, MPFI is not used in diesel engines. Diesel engines use common rail direct injection (CRDi) instead.
Q. Is multi-point fuel injection the same as a direct injection?
The main difference between MPFI and Direct injection is that in the MPFI system, the fuel is injected into the intake manifold while in the direct injection system, the fuel is directly injected into the cylinder.
