Fuel Injection 101: How Fuel Injection Works in Diesel Engines

4-Stroke-Engine 1

4-Stroke-Engine 1 (Photo credit: Wikipedia)

Internal combustion engines, known as carburetors, used to run on blended fuel and air during the 80’s and 90’s. They have been replaced, though, by the fuel injection system that pumps fuel under high pressure so as to run into internal combustion engines.

Diesel engines initiate ignition, thus burn the fuel by utilizing the injected compression’s heat into the combustion chamber, while both gas and petrol engines use a spark plug so as to ignite the pre-mentioned mixture of fuel and air. The high compression ratio of diesel engines is held responsible for their exceeding thermal efficiency, when compared to either external or internal combustion.

Once air enters the diesel engine’s combustion chamber, it is compressed in high compression ratio the size of 15:1-22:1, releases pressure the size of 40 bars (while petrol engines produce up to 14bars) and heats the air to 1,022oF in a pre-chamber or a piston. At the highest level of the compression stroke, inside the combustion chamber, the compressed air gets injected by fuel. Then, the fuel is broken down to small drops that get evenly distributed, via a fuel injector. Those small drops get their surfaces vaporized by the compressed heat and start a series of vaporization and ignition until they are completely burnt in the combustion chamber.

The typical diesel sound that feels like a knock is due to the delay of the beginning of the vaporization process during ignition, which happens as vapors reach the temperatures of the ignition and result to pressure increase above the piston, which is then driven in a downward position to supply the ABS system with power.

When compression is made in high levels, combustion happens and there is no need to be separate ignition system. Similarly, the engine’s efficiency is increased due to upper levels of compression ratio.

Compression ratios are high because pre-ignition is prevented, as air and fuel are not compressed in diesel engines, since only air is compressed and fuel enters the cylinder just before TDC.

High levels of fuel pressure are reached due to mechanical pumps and then non-compressed air injectors, which are activated when pressure is applied on them, deliver the fuel to the combustion chamber. The rate that fuel is delivered is controlled by electronic or mechanical governors.

One can find either a 4-stroke or 2-stroke version of a diesel engine. However, modifying an EFI engine can be done by taking the duty-cycle and injectors’ pulse duration (controlled by the ECU) into close consideration.

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