How Fuel injection get’s on !
The Journey of fuel from Fuel tank to the combustion cylinder has seen several considerable changes to meet the desired outcomes, let it be emission norms or performance dynamics both affect fuel injection significantly.
Petrol and Diesel both have a different chemical composition, Moreover, the air-fuel mixing, compression ratio, and combustion process are very distinguished. Hence the fuel injection Systems for both of them are different. So let’s consider then individually
Have combustion temperatures of range 130-250⁰C.
Injection Systems-Fuel can transcend towards engine by different systems involving different forces, namely
- Gravity Injection- The fuel tank is mounted at the highest position from where the fuel drops into the carburetor float chamber by gravity. Confined to the two-wheeler.
- Pressure System- Here pressure is created using engine exhaust or a separate air pump. For starting, the pump is primed by hand. It is due to the pressure thus created that the fuel flows to float chamber of the carburetor. The tank can be placed at any suitable location.
- Vacuum System- This system uses engine suction for sucking fuel from the main tank to auxiliary fuel tank from where it flows by gravity to carburetor float chamber.
-Both of these systems are obsolete now
- Pump System- In this system, a steel pipe carries petrol to fuel pump which pumps it into the float chamber of carburetor through a flexible pipe.
- Fuel injector system- Here the fuel is atomized by means of an injector nozzle and then delivered into an air stream. Separate fuel injectors are used for each cylinder while the mixture under different load and speed conditions are controlled electronically. It replaces the carburetor.
- When we press the accelerator pedal the ECU immediately adjusts the fuel rate in anticipation of air about to enter the engine.
- Sensors monitor the amount of air that enters the engine and also the amount of oxygen in the exhaust. This information helps to fine-tune the fuel delivery to achieve just the correct fuel ratio.
- The petrol is injected by an injector, which an electronically controlled valve. The injector is supplied with the petrol under high pressure by the fuel pump.
- The time for which the fuel injection is determined by the ECU.
There are various other factors on which it can be classified-
According to Location of injectors-
- Throttle Body Injection- Here the injector assembly is attached to a throttle body and placed on the intake manifold. It simplifies the construction of engine blocks and doesn’t obstruct hot spots near the valves affecting the cooling water jacket size. Less costly and less precise.
- Port Injection- Here the fuel is sprayed into each intake port on the manifold side of the inlet valve. It allows more time for mixing of air and petrol. This system is more precise as in this fuel delivery does not depend on air to carry the fuel through the intake manifold.
- Direct Injection- Here the Injector is placed directly into the cylinder. The intake valve allows only air into the combustion chamber and fuel is sprayed. Mixing of fuel takes place inside the chamber itself. The piston crown in such engines is normally designed to create a swirling vortex to help mix the fuel and air before combustion, it also has a cavity on it for ultra clean burn conditions.
According to the Number of Injectors
- Single Point- It consists of a single injector for entire engine mounted above throttle butterfly valve, feeding engine in a manner similar to carburetor system.
- Multi-Point Injection- Here each cylinder has separate injector mounted in the inlet port. The injectors direct fuel onto the back of the inlet valves giving improved mixture preparation, the fuel can also be directly sprayed into the combustion chamber.
Diesel Engine has auto-ignition temperature of 210⁰C. This Engine doesn’t have any ignition source the air is compressed until it reaches the auto-ignition temperature and then fuel is sprayed.
The fuel injection in the diesel engine is done mainly by two common mechanisms-
- Common rail Fuel injection System- This system consists of a high-pressure pump, injectors, a rail, and an electronic control unit. The fuel is made readily available for injection in a rail common for all the injectors, the fuel in the rail is kept at high pressures of 100 MPa created by the high-pressure pump.
- Advantages include-
- Clean and highly efficient fuel injection due to short spraying distance and multiple injections.
- High engine power smooth working with low consumption and emissions.
- Advantages include-
- Individual pump fuel injection System- Here fuel is drawn from the fuel tank by means of fuel feed pump which is operated from injection pump camshaft. The fuel is first passed through the filter and then a definite quantity of fuel is injected into individual cylinders according to the firing order, through the injectors fitted on them.
The Bi-fuel System offering CNG/LPG as an alternative fuel. It has second controlling unit alongside the original ECU. It manages the alternative fuel supply, optimizing engine performance and subsequent emissions.
As we switch to CNG mode the ECU sends the signal to the fuel pressure regulator.
The fuel passes through the filter and later enter the CNG Rail at a pressure of 7 bar.
Then fuel from here is further injected into the combustion chamber through CNG injectors.
After combustion, the exhaust exits from the exhaust system.
The system is somewhat identical for LPG System. Both CNG and LPG have 5 Valves for safety.
Also, research is going on to improve the current market trend and also cater to the future demands more efficiently.
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