Multi-point fuel injection: What type of injection is it?
Multi-point fuel injection is denoted by the MPI (Multi Point Injection) abbreviation. In this type of injection, fuel is injected before the intake valve using injection valves assigned to individual cylinders.
This means that one injection valve is assigned to each cylinder, which delivers the required fuel for that cylinder.
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How does multi-point fuel injection work?
As mentioned, with multi-point injection, the fuel is injected before the intake valve, ensuring the same composition of the working mixture for each cylinder. With MPI multi-point injection, the fuel injection pressure is 0.2 to 0.3 MPa (2 to 3 bar) above the intake manifold pressure.
Among the advantages of multi-point fuel injection, in addition to the precise dosing of the amount of fuel for each cylinder, we can also include the exact timing of the fuel injection. Injection timing and the moment of fuel injection are essential for optimizing consumption and emissions.
Multipoint fuel injection can thus be divided according to the moment of fuel injection into:
- Simultaneous injection
- Group injection
- Sequential injection
- Individual injection
1. Simultaneous injection
With this type of injection, all injection valves inject fuel simultaneously, regardless of the ongoing stroke of the cylinders. However, the fuel dose is divided into two parts to compensate for the differences in the mixture preparation time for individual cylinders.
Crankshaft: What is it for, and what forces must it withstand?
Simply put, half of the fuel dose is injected during one rotation of the crankshaft and the other half during the second rotation.
2. Group injection
In group injection, the injection valves of individual cylinders are divided into groups. These groups of injection valves inject the entire amount of fuel into the cylinders simultaneously during one engine cycle.
3. Sequential injection
According to the ignition order, the injection valves inject fuel in front of the intake valve individually, with the same advance for all cylinders. However, the entire charge of fuel is injected only once during one cycle before the start of each intake phase.
4. Individual injection
The individual injection works similarly to sequential injection, allowing you to individually influence the injection time and fuel pre-injection for each cylinder.
This type of fuel injection makes it possible to compensate for irregular engine operation caused by different conditions when filling the cylinders.
Conclusion
From an evolutionary point of view, we can place multi-point injection somewhere in the middle between single-point fuel injection and direct fuel injection. To this day, multi-point injection is the most widespread fuel injection for spark-ignition engines.